In traditional water gilding, bole is the colored clay and glue layer that sits between gesso and gold leaf. It is not a cosmetic filler. It is an interface that controls how the gold adheres, how it burnishes, and how its color appears in light. In this article, we review the section from the booklet Gilding Notes: The Traditional English Method by Judith Wetherall.

Wetherall describes bole as fine “pipe” clay bound with animal glue, whose tiny plate-like particles can slide over one another under pressure during burnishing [Wetherall 2025, p. 27].

Gold leaf is extremely thin, and according to Jane Wetherall, light can pass through it and interact with the color beneath. Therefore, the bole tone, thickness, and burnish have a direct, visible effect on the finished surface [Wetherall 2025, pp. 27–28]. The belief that substrate color influences the gilding is widespread. However, a comprehensive study provides clarity on this issue, unraveling the misconceptions and exploring the intricacies of gilding techniques and materials in the medieval era. Read the article, The Influence of Gilding Base Color on Gilded Surfaces: Insights and Misconceptions.

Historically, bole also reduces the porosity of the gesso. It slows the absorption of size water, so the gilder has enough open time to lay the leaf cleanly [Wetherall 2025, p. 28]. Without that control, the water sinks too fast, the gold bridges, and the surface becomes patchy or unburnishable.

Traditional Bole Colors in Water Gilding

Historically, European ateliers used local clays, and their geology still shows in historic frames and altarpieces. Wetherall notes that the most prized bole historically came from Armenia. It produced a rich, deep red color and a particularly good burnish, which made it expensive and closely guarded in workshops [Wetherall 2025, p. 28].

By contrast, English clays needed help. English bole recipes added graphite (“black lead”) and mutton suet to pipe clay and earth pigments to improve burnish and modify sheen [Wetherall 2025, p. 28]. Yellow clay was often used, with red or black reserved for highlights. Yellow burnishes poorly, so it was left matte, while red and black clays on accessible peaks were taken to a high polish [Wetherall 2025, pp. 28–29].

Today, modern commercial boles are usually pastes made from refined clays and sold in colors named after historic uses (for example, “Georgian Orange”) [Wetherall 2025, p. 29]. However, these names are marketing shorthand, not strict archaeological labels; the same hue can appear in fifteenth‑century Italian work as well as Georgian English examples.

Table 1. Typical bole colors and historic uses (after Wetherall)

For conservation and historically accurate reconstructions, matching period-appropriate clay color and behavior is as important as matching gold.

Preparing Bole for Water Gilding

Historically, bole was sold as dry cones. The gilder soaked, ground, and sieved the clay before mixing it with glue size [Wetherall 2025, pp. 28–29]. Today, most artists will start from commercial paste bole. Nevertheless, the preparation principles remain the same.

Wetherall recommends using rabbit-skin or parchment glue, prepared slightly weaker than glue for gesso or chalk ground, because too-strong size makes a glassy, brittle film that does not take burnishing well [Wetherall 2025, p. 30]. Soak the glue granules for several hours or overnight, then dissolve them in a bain-marie or carefully in a microwave oven, and add them gradually to the clay in a white vessel so that the color can be judged accurately.

Unlike gesso, bole is not judged solely by viscosity. Instead, the gilder evaluates coverage and tone. A test stroke over scrap gesso should produce a translucent veil: the white ground should still “grin through” after a single coat [Wetherall 2025, p. 30]. If the layer is opaque or heavily streaked, the mixture is too clay‑rich or too thick.

Once the color and coverage are correct, the bole is strained through fine silk or mesh to remove grit and agglomerates. Wetherall suggests warming the strained bole gently so it remains fluid but not hot. Overheating risks skinning and bubbles [Wetherall 2025, p. 30].

Glair (settled beaten egg white) can be used to temper bole instead of glue, especially in Italian practice, but it is harder to control and more brittle. Therefore, for contemporary studio work, protein glue remains the more flexible and predictable binder.

Applying and Polishing Bole for Water Gilding

Before applying bole, the gesso must be fully dry, shaped, and smoothed. Wetherall advises rubbing flat areas with fine silicon carbide papers from about P120–P400 and “ragging” carved surfaces with damp silk, using minimal water [Wetherall 2025, p. 27]. The goal is a clean, continuous surface without ridges, knife marks, or powdery areas.

Next, apply the bole in thin, swift strokes with a soft brush. Historically, a squirrel mop was commonly used, although soft nylon or sable flats also work when used lightly [Wetherall 2025, p. 30]. The brush should hold only a modest charge of liquid. The gilder sweeps rapidly across the surface, avoiding reworking fresh areas until they dry matte.

Wetherall, therefore, recommends the following layering scheme for traditional English gilding work [Wetherall 2025, pp. 29–30]:

1. One to three layers of yellow bole over the entire gessoed surface, until all white is covered, but the layers remain thin.

2. One or two layers of red bole over high points that are intended for burnishing.

3. Optional touches of black bole on very selective highlights, such as the outer tips of petals, when a sharp, cold flash of burnish is desired.

Each layer is applied when the previous one is dry to the touch. Unlike gesso, bole can be thoroughly dry between coats; there is no penalty for bubbles. Total bole layers rarely exceed four or five [Wetherall 2025, p. 30].

After complete drying, the bole must be polished. Wetherall stresses that this stage is about levelling and nib removal, not pre‑burnishing [Wetherall 2025, p. 30]. Suitable tools include:

• A cut-down bristle house-paint brush with its ferrule taped;

• 1000‑grit wet‑and‑dry paper, used gently;

• Grade 0000 oil‑free steel wool.

The object is a satin, even surface, free of brushstroke ridges. Using an agate burnisher on bare bole dulls the clay, risks glazing the glue, and spoils the later burnish under gold.

Water Size in Traditional Water Gilding

In water gilding, gold adheres because the bole is momentarily rewetted with a dilute glue solution called size water. Wetherall’s typical English recipe uses approximately one teaspoon of glue size to half a pint of water plus about one teaspoon of methylated spirits [Wetherall 2025, p. 31]. The alcohol lowers surface tension, so the water wets the clay evenly instead of beading.

Because craft conditions vary, Wetherall advises adjusting the proportions by how the bole behaves, not by fixed numbers [Wetherall 2025, p. 31]. If the bole absorbs the water immediately and flashes dry, the size may contain too much alcohol or too little glue. If the water beads on the surface, more alcohol is required, or the bole needs further polishing.

Other traditional water sizes include gin and water or water with a trace of glair plus alcohol. Gin evaporates quickly and is suitable only for experienced gilders, since the working window is short [Wetherall 2025, p. 31]. Regardless of recipe, the size must keep the bole uniformly glossy just long enough for the leaf to land and pull down.

Laying Loose Gold Leaf in Water Gilding

Only loose leaf is suitable for water gilding [Wetherall 2025, p. 13]. Wetherall emphasises technique and sequence more than force. The gilder wets an area, then immediately lifts and lays the gold:

• Work from upper surfaces downward so that water size cannot run over the finished leaf.

• Avoid flooding; a shallow, coherent gloss is ideal.

• Hold the gilder’s tip parallel to the surface and move in decisively; the gold will jump to the moisture as the tip nears [Wetherall 2025, p. 31].

She warns against pulling the tip toward the gilder when lifting it, as that motion tears the leaf [Wetherall 2025, p. 31]. If air is trapped, the leaf is gently tamped with a dry sable writer held end‑on at ninety degrees. Using the tip for tamping contaminates its hairs with size and shortens its working life.

Leaf should always overlap slightly so that any seepage of size water occurs under a second sheet of gold, not along a bare bole join [Wetherall 2025, p. 31]. Faulting and patching should be done with pieces as large as practical. Tiny patches invite the accumulation of size, which stains and darkens the surface.

On mouldings and sharp sections, the leaf must be cut and placed so that it folds into hollows rather than bridging them. Wetherall notes that leaf willingly follows a U-shaped groove but tends to crack if forced into a sharp V [Wetherall 2025, pp. 25, 31].

Burnishing Gold Leaf in Water Gilding

Burnishing is the controlled compression of gold, bole, and gesso with an agate or similar polished stone. It creates the characteristic mirror-like surfaces of water gilding. However, the timing is critical. Wetherall describes the ideal state as one where the preparations are neither obviously wet nor bone dry, but retain just enough internal moisture to act as a cushion [Wetherall 2025, p. 32].

She suggests practical tests. The gilder lightly taps the burnisher on a discreet area; the surface should sound hollow and resonant, not soft or silent. In a temperate, moderately humid studio, this window might arrive in fifteen minutes or several hours, and in some cases only after a day or two [Wetherall 2025, p. 32].

Once ready, the burnisher is drawn in smooth, overlapping sweeps, increasing pressure only until a clear shine appears. Wetherall advises working in one dominant direction and finishing each zone completely before moving on [Wetherall 2025, pp. 32–33]. Circular burnishing leaves visible arcs, and overworking can bruise or delaminate the layers.

She also notes:

• Dirty or faceted stones will score the gold.

• Skewings stuck to the burnisher must be removed, usually with industrial methylated spirits.

• Only raised areas and surfaces naturally accessible to the stone should be burnished; leaving enough matte zones preserves modelling and prevents the object from reading as flat metal [Wetherall 2025, p. 33].

The Science Behind Water Gilding

Clay platelets and burnishability

Bole clays are composed of microscopic platelets. Under pressure, these plates can slide past each other and then align, reducing surface roughness and increasing specular reflection.

Studio translation: a well-formulated bole can be compressed into a smooth, continuous plane under the gold. That plane behaves almost like a polished stone, giving a deep, hard-looking shine without needing excessively thick leaf.

Protein glue networks

Rabbit-skin and parchment glues form networks of long, spring-like molecules that swell with water and contract on drying. When they bind clay and chalk, they create a rigid but slightly elastic matrix.

Studio translation: glue strength determines whether the ground behaves as a resilient cushion or a brittle eggshell. Therefore, keeping bole glue slightly weaker than gesso glue helps the burnished interface compress rather than crack.

Surface tension and wetting

Pure water tends to bead on oily or very smooth surfaces. Adding alcohol lowers surface tension, so water spreads as a continuous film across the bole.

Studio translation: a small amount of alcohol in size water gives you even wetting and a more predictable lay of the leaf. However, too much alcohol shortens the open time and can starve the bole of moisture.

Transmitted light and bole color

Standard gold leaf is thin enough that part of the incident light passes through it, interacts with the underlying bole, and then re-emerges. That interaction shifts the perceived hue and depth.

Studio translation: red bole warms and deepens the gold; yellow gives a neutral, “clean” metal; black sharpens contrast but can cool and gray the tone. Consequently, the choice of bole is a critical color decision, not just a historical detail.

Moisture, humidity, and burnishing windows

As the gesso–bole stack dries, water migrates outward and evaporates. Ambient humidity and temperature strongly affect how long the layers remain in the “cushioned” state when burnishing is possible.

In dry, heated studios, the burnishing window may be short and arrive quickly. In cool, humid weather, the same surface may need many hours before the agate gives a clean polish. Therefore, you must test, not rely on fixed times.

Critical Appraisal of the Water Gilding Source

Scientific merit

Wetherall’s notes are explicitly practical guidelines compiled over more than forty years of professional work rather than formal experiments [Wetherall 2025, Foreword]. She does not report sample sizes, instrumentation, or quantitative measurements of glue strength, moisture content, or leaf thickness in the bole and burnishing sections. Instead, she offers phenomenological criteria such as resonance when tapping with a burnisher, or the “grin” of gesso through bole [Wetherall 2025, pp. 30–32].

This experiential approach has clear limitations. There are no controlled comparisons of different clays under identical conditions, and no statistical analysis of failure rates. Certain historical recipes, such as the use of gin as size water, are described but not verified with ageing studies or mechanical testing [Wetherall 2025, p. 31]. Therefore, the notes should be read as a distilled record of best practice in one well-documented craft tradition, not as a universal, lab-validated protocol.

External validity

Despite these limits, the external validity for studio practice is high. Wetherall’s descriptions are rooted in repeated work on historic English frames, furniture, and architectural decoration, often under conservation constraints [Wetherall 2025, Foreword]. Her observations about bole colors, burnish behaviour, and glue strength align with the experience of many gilders working in similar climates and with comparable materials.

However, contemporary studios may introduce variables that are under-represented in the notes. These include modern MDF supports, synthetic glues, premixed acrylic sizes, climate-controlled interiors, and LED lighting. Wetherall briefly warns that PVA-based sizes stay indefinitely soft and are unsuitable for gilding, but she does not systematically test modern products [Wetherall 2025, p. 35]. Artists adopting her procedures must therefore adapt them cautiously when substituting materials.

Facts versus interpretation

Facts from the text include:

• Bole is a mixture of colored clay and protein glue, applied over gesso and under gold [Wetherall 2025, p. 27].

• Yellow bole is generally used overall; red and black are placed on highlights according to burnish qualities [Wetherall 2025, pp. 28–30].

• Wetherall’s size water recipe combines weak glue, water, and methylated spirits, adjusted by observation [Wetherall 2025, p. 31].

• Burnishing should be attempted only when the preparations give a hollow, resonant sound and resist gentle touch without feeling soft [Wetherall 2025, p. 32].

Interpretations in this review include:

• Treating bole as a deliberately engineered interface layer, comparable to a controlled ground in painting.

• Emphasising bole color selection as a primary color-design decision for contemporary work, not merely a historical convention.

• Arguing that glue strength calibration is central to mechanical stability and that this area would benefit from quantitative testing.

• Highlighting environmental control (humidity and temperature) as variables that could be formalised, rather than left entirely to intuition.

These interpretations build on Wetherall’s descriptions but extend them toward a more explicitly materials-science mindset.

Best-Practice Water Gilding Guidance for Contemporary Artists

The following protocol adapts Wetherall’s traditional English method for professional studios today.

Support and Gesso Preparation for Water Gilding

1. Choose a stable, appropriate support. Use seasoned softwoods, hardwoods such as lime or oak, or high-quality plywood or MDF for panels. Avoid oily species and woods treated with fire retardants, which can repel gesso [Wetherall 2025, p. 21].

2. Size bare wood with hot rabbit-skin glue at about 1:10 by volume, on both faces of panels. Allow thorough drying [Wetherall 2025, p. 22].

3. Apply at least eight coats of gesso on panels, more on areas intended for re-cutting. Lay coats in alternate directions and keep gesso near body temperature to minimize bubbles [Wetherall 2025, pp. 23–25].

4. Allow to dry overnight. Then smooth flat zones with fine silicon carbide paper, and lightly ragged carved zones with damp silk, using minimal water [Wetherall 2025, p. 27].

Health note: rabbit-skin glue dust and gesso powder can irritate the respiratory system. Use a well-fitted dust mask when sanding.

Mixing and Applying Bole for Water Gilding

5. Prepare rabbit-skin glue slightly weaker than that used for gesso. Soak, melt without boiling, and keep warm [Wetherall 2025, p. 30].

6. In a white vessel, gradually add warm glue to the paste bole while stirring gently with a soft brush. Aim for consistency similar to that of whole milk [Wetherall 2025, p. 30].

7. Test on scrap gesso. Adjust with more glue (if patchy and too absorbent) or more bole (if streaky and weak in color). Strain through fine silk or mesh.

8. Apply one to three thin coats of yellow bole over all gesso until no white remains. Allow each coat to dry matte [Wetherall 2025, p. 30].

9. Apply one or two coats of red bole on all highlights intended for burnishing. Add black bole only where a very cold, bright flash is desired, and then only on the highest points [Wetherall 2025, pp. 28–30].

10. Let the bole dry thoroughly, then polish gently with a cut-down bristle brush or very fine abrasive. Remove nibs without cutting through to gesso.

Size Water and Gold Application in Water Gilding

11. Prepare the gilding size by mixing weak glue size with clean water and a small amount of alcohol. Adjust until it wets the bole smoothly without severe beading or instantaneous sinking [Wetherall 2025, p. 31].

12. Work in manageable sections. Wet the bole to an even gloss using a gilder’s mop, avoiding runs and puddles.

13. Immediately pick up loose gold leaf with a squirrel-hair tip and lay it from the top downward. Overlap leaves slightly to conceal joins and to trap any seepage beneath metal [Wetherall 2025, p. 31].

14. Tamping is used only when necessary to release trapped air. Use a dry sable writer held end-on and avoid contaminating the tip with size [Wetherall 2025, p. 31].

15. For mouldings and deep profiles, cut the leaf and position it so it drops into the hollows rather than bridging them.

Ventilation note: methylated spirits and other alcohols are flammable and produce vapors. Work away from ignition sources and ensure adequate ventilation.

Burnishing Strategy in Water Gilding

16. Allow the gilded work to reach the elastic-cushion stage before burnishing. Test readiness by gently tapping an inconspicuous area and listening for a hollow ring, then by light touch with a fingertip [Wetherall 2025, p. 32].

17. Use a clean, highly polished agate with an appropriate shape (dog-tooth, pencil, or book-edge). Inspect under raking light for chips or facets.

18. Burnish in long, even strokes, gradually increasing pressure until a shine appears. Keep strokes largely aligned and avoid tight circles that leave visible arcs [Wetherall 2025, pp. 32–33].

19. Burnish only where the tool naturally reaches: ridges, beadings, outer curves. Leave shadowed hollows and recesses, matte to support visual modelling [Wetherall 2025, p. 33].

20. Stop immediately if resistance increases sharply or if the gold greys; this indicates that the bole is being disturbed or that layers are too dry.

Safety, Storage, and Display for Water Gilding

• Keep protein glues refrigerated between uses and discard at the first sign of strong odor or mold [Wetherall 2025, p. 20].

• Avoid rapid environmental swings. Large changes in humidity or temperature can stress the gesso–bole–gold stack and increase the risk of cracking over time.

• Store finished gilded works in padded supports to protect burnished areas from abrasion. For display, balance lighting so that specular highlights do not obliterate modelling.

Adapting Water Gilding to Modern Materials

Many contemporary artists prefer not to use animal glues or to work on supports that were rare historically. The principles in Wetherall’s book still translate, but some substitutions are riskier than others.

• Synthetic sizes: Wetherall reports that PVA emulsions and similar synthetic sizes form uneven films, dry irregularly, and remain permanently soft, leading to inferior, unstable gilding [Wetherall 2025, p. 35]. Therefore, these should be avoided for serious work, especially if the object is expected to have a long life.

• Gelatin: high-grade gelatins behave similarly to refined animal glues and can substitute for rabbit-skin glue in bole preparation when prepared carefully [Wetherall 2025, p. 20]. However, bloom strength and impurities vary, so tests are essential.

• Premixed boles: modern paste boles save grinding time but conceal clay character. Because quality can only be assessed after application and burnishing, artists should test each new batch on sample boards before committing to important work [Wetherall 2025, pp. 28–30].

• Alternative supports: MDF, high-quality plywood, or plaster can all be used if appropriately sized. The porosity of plaster demands extra glue sizing before gesso [Wetherall 2025, p. 21].

In every case, the key is to preserve the functional sequence: stable support, elastic gesso cushion, thin and well-bound bole, controlled wetting, and correctly timed compression.

Water Gilding with Bole

Overall, Wetherall’s sections on bole and burnished water gilding capture a mature English craft tradition in a concise, practical way. For contemporary artists, her book offers not only recipes but a way of thinking: treat each layer as an active component with mechanical and optical roles, test constantly, and allow timing and touch to guide decisions.

When applied thoughtfully, these methods still produce gilded surfaces that balance brilliance with depth. They respect historic practice while leaving room for measured innovation, provided that substitutions honour the underlying physics of clay, glue, water, and gold.

Bibliography

Wetherall, Judith. Gilding Notes: The Traditional English Method. Los Angeles: The Getty Conservation Institute, 2025.

This booklet gathers practical instructions for traditional English water gilding, including the preparation of gesso and bole, and the application and burnishing of loose gold leaf. It is directly relevant for artists and conservators seeking historically grounded yet studio-tested methods for bole formulation and gilding technique.

Artists have long valued the subtle beauty and durability of natural pigments. For centuries, colors derived directly from minerals, plants, and insects have given artwork a richness that synthetic dyes struggle to reproduce. Today, as sustainability and eco‑consciousness take centre stage, there is renewed interest in earth‑based hues; natural pigments are making a comeback across art and design. These colorants offer unique, muted tones and are typically produced with minimal environmental impact. This shift toward natural materials is reflected in contemporary art trends: many artists now prioritise eco‑friendly materials and ethical sourcing, creating works that use natural materials and sustainable practices.

In response to this movement, Rublev Colours introduces a collection of five Armenian earth oil paints made with pure mineral pigments and linseed oil. The colors—Yellow Travertine, Orange Travertine, Red Barite, Olive Umber, and Violet Lalvarit—are derived from geological formations in the Caucasus region of Armenia. Each paint highlights the inherent qualities of its source rock or earth, bringing artists closer to the origins of their materials. To accompany this article, Natural Pigments will share videos of the tubes being squeezed onto canvas and spread with a palette knife, along with drawdown images showing each color at full strength and tinted with titanium white.

What Armenian earth colors mean to artists

• Earth‑derived colors: All five paints are made from naturally occurring mineral pigments, connecting artists to a long history of using ochres, umbers, and other iron oxides.

• Sustainability: Natural pigments are produced with minimal environmental impact, making them a more sustainable choice.

• Authentic hues: These pigments provide rich, earthy tones and subtle variations, lending depth to the painting. Many have been used since prehistoric epochs and have stood the test of time.

• Local geology: The colors come from specific Armenian deposits—travertine springs, barite‑rich clays, iron‑manganese earths, and volcanic andesite—offering a geographical story behind each tube.

Yellow Travertine

Travertine is a form of limestone precipitated from mineral springs. In the Lori Province of Armenia, deposits of pale travertine contain small amounts of iron oxide that produce a soft yellow‑beige tint. The pigment is a natural, inorganic earth classified in the yellow iron‑oxide family (Colour Index PY43) and consists mainly of calcium carbonate with traces of silica and iron. When ground for oil paint, the pigment has a mean particle size of about 8 μm and an oil absorption of roughly 24 g per 100 g of pigment. This fine particle size produces a smooth film and semi‑opaque coverage.

Rublev Colours’ Yellow Travertine Oil Paint captures the delicate warmth of this stone. In mass tone, it appears a pale straw color; when tinted with titanium white, it yields gentle beige tints ideal for mixing skin tones, atmospheric landscapes, or luminous neutrals. The linseed oil binder gives a moderate drying rate and a slightly matte finish. As with all Rublev Colours paints, no additives, fillers, or extenders are used—just pigment and oil.

Origins

Travertine forms in mineral springs when dissolved calcium carbonate precipitates out of solution and forms porous stone—a form of calcite. The Armenian deposits used for this paint originate from spring waters in the Lori Province. These travertine beds have been quarried since antiquity for building and ornament; now they also provide a unique artist pigment.

Orange Travertine

Like its yellow sibling, Orange Travertine comes from the same travertine springs but contains higher levels of iron oxide, which give it a warm orange hue. This unusual earth pigment is composed not only of calcite but also of germanite. Germanite is a rare, copper-iron-germanium sulfide mineral with the chemical formula Cu₂₆Fe₄Ge₄S₃₂. The pigment is classified as a natural inorganic earth (Colour Index PY43) and has similar physical properties to the yellow variety: mean particle size around 8 μm, density around 2.7 g/cm³, and oil absorption about 24 g per 100 g pigment. The composition, which includes calcite (calcium carbonate) with increased iron content, yields a color range from burnt orange in mass tone to soft apricot when mixed with white.

Rublev Colours’ Orange Travertine Oil Paint displays a semi‑opaque, medium‑strength tinting power. It is perfect for mixing warm highlights, autumnal landscapes, and lively flesh tones. Because the pigment is derived from stable iron oxide, the paint offers excellent lightfastness and permanence.

Origins

Both the yellow and orange travertine pigments originate from Lori Province, Armenia, where mineral springs deposit layers of calcite enriched with iron. These naturally colored stones connect artists with the geological processes that created them.

Red Barite

Red Barite is unlike typical red ochre. The clayey earth from northern Armenia contains hematite (red iron oxide) mixed with quartz and barite (barium sulfate). The presence of barite, rather than calcite, distinguishes this pigment; barite’s high density adds body to the paint and contributes to its opacity. The pigment’s colorant is hematite (Colour Index PR102), giving a deep, earthy red. Analyses show a mean particle size of about 10 μm and a composition of approximately 41.67% barite (Ba), 28.16% iron, 16.14% sulfur, 8.79% silica, and 2.06% aluminum.

The resulting Red Barite Oil Paint is a powerful, semi‑opaque red with a slightly granular texture. In mass tone, it appears as a warm brick red; when extended with white, it produces pinkish‑terracotta tints. The paint’s high density gives it body without requiring much additional oil, and it dries at a moderate rate.

Origins

This pigment is collected from earth deposits near Akhtala in the Lori Province of Armenia. Local miners have long extracted barite for industrial use; the mineral’s vivid color also makes it an exceptional artist’s pigment.

Olive Umber

Umber pigments derive their color from iron and manganese oxides. Olive Umber contains α‑Fe₂O₃ (iron oxide) and MnO₂ (manganese oxide) and is listed under Colour Index PBr 7. The combination of iron and manganese gives this earth a greenish‑brown hue, deeper and cooler than standard raw umber. Physical data show a particle size distribution with 80–85 % of particles under 15 μm and 15–20 % between 16 and 29 μm, with a density ranging from about 3.3–4.3 g/cm³.

In oil, the pigment yields a semi‑opaque paint with a fast drying time, thanks to the catalytic effect of manganese. Rublev Colours’ Olive Umber Oil Paint has strong hiding power and a dark, olive‑brown mass tone. When mixed with titanium white, it produces muted khaki and sage tints ideal for naturalistic shadows, foliage, and subdued palettes.

Origins

The olive‑umber pigment used in this paint comes from Armenian earth deposits rich in iron and manganese oxides. The natural combination of minerals gives this color its distinctive greenish cast.

Violet Lalvarit

The most unusual of the new colors, Violet Lalvarit, is ground from andesite lava rock found near Mount Lalvar in Armenia. Lalvarit is not a formally recognised mineral name but rather a local term for a unique grey‑violet andesite containing iron and manganese oxide impurities. The pigment contains about 30.26% silica, 8.17% aluminium, 5.89% iron, 1.59% potassium, and 1.17% manganese. It has a mean particle size of around 8 μm, a Mohs hardness of 7, and a relatively high oil absorption of 32 g per 100 g pigment. These physical characteristics create a smooth, yet slightly absorbent, paint film.

Rublev Colours’ Violet Lalvarit Oil Paint delivers a semi‑transparent grey‑violet tone with subtle warm undertones. In mass tone, it resembles dusty plum; when tinted with white, it shifts toward cool lilac and mauve. The hardness of the andesite gives the paint a delicate sparkle and ensures excellent permanence.

Origins

This pigment is sourced from andesite lava flows in the Alaverdi ore region near Mount Lalvar, a mountainous area of the Lori Province. The rock’s violet cast arises from iron and manganese oxides present in the lava.

Earth colors for a grounded palette

Natural pigments connect artists to the earth and to centuries of color‑making tradition. As sustainable art practices gain momentum, materials that are produced with minimal environmental impact become increasingly important. The new Armenian earth oil paints from Rublev Colours offer a palette of authentic hues—yellow, orange, red, olive, and violet—each rooted in Armenian geology and free from synthetic additives. Whether you’re painting luminous skin tones, rugged landscapes, or subtle shadows, these colors provide unique qualities that synthetic pigments can’t replicate. With their rich histories and eco‑friendly credentials, they invite you to explore a deeper connection between your materials and the natural world.

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 Granulation is the visible mottling that appears when pigment settles unevenly during a wash. You see soft speckles, pools, and lighter islands. It changes how edges read, how glazes alter hues, and how a sky or stone texture feels. Because it depends on paper, dilution, and handling, it often surprises even experienced painters. Our method measures granulation in a way you can repeat, compare, and trust—so you can choose watercolor paints with far less guesswork.

What we mean by “granulation”

Granulation is the pattern of tone change caused by pigment grains gathering in some small areas and thinning in others as the wash dries. It differs from flocculation (grains clumping in the liquid before or after they are on the paper) and from staining (how strongly a pigment embeds into fibers). Here, we measure the visible result on the dry paint film—not the behavior while wet.

Why we built an objective scale

Artists need objective evaluations of paint behavior and consistency. Brushstrokes vary, paper lots differ, and lighting shifts perception. We use a method that produces a number first, then a word description. The number, the Granulation Index (GI), comes from a scan of a watercolor swatch prepared under carefully controlled conditions that reduce paper and tone effects. The index allows us to categorize the granulation (see below). The same method applies to every color and every paper we test, so results from different sessions can be compared directly.

Summary of the method

Figure 1 — Workflow overview. End-to-end process: from a standard swatch to a Granulation Index and granulation category.

Materials and setup

1. Watercolor paper under test—the baseline is taken on the same sheet and in the same scan as the color. Since we are not rating the granulation effect on any specific watercolor paper, we use Whatman No. 42 filter paper, since it is also used in lightfastness and staining tests. Note 1
2. Paint from the tube or a freshly re-wetted pan
3. Deionized or distilled water.
4. Round brush (size 12) for pre-wet only.
5. Pipettes (1 mL for the 0.10 mL bead; additional for pre-wet).
6. Pencil (orientation mark).
7. Flatbed scanner capable of 16-bit/channel at 1200 dpi with all automatic corrections off.
8. Optional: IT8 target and profile for color-managed scanning.

Preparing the watercolor swatch

Mount the watercolor paper on a clean board using low-tack tape around the perimeter. Mark the 12 o’clock position for orientation. Pre-wet the entire circle with deionized water to an even satin sheen (no puddles), and record the amount of water used (mL). Set the board to 15° with the 12 o’clock edge raised. Prepare the paint at 1:8 (mass ratio of paint to water); mix for 60 seconds, then rest for 2 minutes. Using a calibrated pipette, dispense 0.10 mL of the mixture along the top arc just inside the paper edge. Do not manipulate the flow; allow gravity to carry the bead down the wetted circle. Cover from dust and air-dry undisturbed, then condition 24 hours at room conditions before scanning. Here are the steps in order:

1. Mount the filter circle (we use 110 mm diameter filter paper) on a clean board with low-tack tape around the perimeter.

2. Mark the top for orientation.

3. Pre-wet the entire circle with deionized water to an even satin sheen (no puddles) and record the mL used.

4. Set the board to 15° with the 12 o’clock edge raised.

5. Prepare the paint at a 1:8 (paint-to-water, by mass) ratio. Mix the water and paint for 60 seconds, then allow to rest for 2 minutes.

6. Using a pipette, dispense 0.10 mL of the mixture along the top just inside the paper edge. Do not manipulate the flow—let gravity carry the paint down the wetted paper.

7. Cover from dust and air-dry undisturbed; then acclimate for 24 hours at room conditions before scanning.

Notes on consistency: Keep the brush angle, speed, and pressure the same for every color. Also, stir the stock wash before each new swatch. Replace the water if it becomes dirty. Meanwhile, note the room temperature and humidity, since drying speed can change granulation strength.

Scanning the swatch and the paper

Scan the entire dried swatch and the paper-only at 1200 dpi, 16-bit per channel (48-bit RGB), saving as TIFF with all automatic corrections turned off (sharpening, auto-levels, dust/grain removal). If your workflow is profiled, embed the scanner ICC; otherwise, scan linear unmanaged and record model, software, and settings so runs can be repeated.

Selecting the test area on a swatch

On filter paper, the wash doesn’t settle in the same place each time, so we follow the same visual rules rather than fixed coordinates. We choose one 1-inch square that represents the broad mid-tone field of the wash—where granulation is most visible and not distorted by edge effects.

Where we would place the square on this swatch (Alizarin Crimson):

• Good choice A: the left square, roughly one third in from the left edge and halfway down from the top arc—an even, pink mid-tone with clear grain but no white channels or bead marks.

• Good choice B: the right square, between the central white “river” and the right edge, again in the middle third vertically. We select the most typical representative of the overall mid-tone; they should read similarly.

Zones to avoid on this and any swatch:

• the top band where the bead first touched (darkest, compressed texture),

• the pale tail near the bottom (too thin to show the pattern),

• white channels, backruns, dust, creases, or tape marks,

• the outer paper edge of the circle.

Removing the paper’s influence:
On the same sheet and scan, place an identical 1-inch square on bare paper near the paint square (but away from edges/tape). That tells us how much mottling is due solely to the paper. We subtract that baseline (in quadrature) from the paint’s variation, so the number reflects pigment-driven granulation rather than paper texture.

What the result means:
From the paint tile, we measure how much the lightness varies and scale it by the square’s average lightness. After removing the paper’s values, you get the Granulation Index (GI).

• Higher GI ⇒ more visibly mottled, grainy wash.

• GI near zero ⇒ as even as the paper itself at that spot.

Quality check:
If two nearby mid-tone patches both look representative and you’re unsure, measure both. If their GI values differ by more than ~10% (relative), discard that swatch and remake it—this prevents “cherry-picking” and keeps the method honest.

The math we use

Figure 3 — From Texture to Granulation Index. Color and grayscale images comparing paint and blank paper tiles. After correcting the difference in the paper, Alizarin Crimson shows no granulation.

We measure tone variation in L* within the paint tile and remove the paper’s own texture. The result is a paper-corrected coefficient of variation, which we call the Granulation Index (GI).

Let SD_p be the standard deviation of L* for the paint tile and SD_b for the blank paper tile on the same sheet/scan. Let Mean be the mean L* of the paint tile.

We report GI either as a fraction (e.g., 0.125) or as a percent (12.5%)—but we use the same choice consistently throughout the article. If SD_p ≤ SD_b, GI = 0 (indistinguishable from paper).

Another illustrative example

Suppose the paint area has SD_p = 2.8, the blank paper has SD_b = 1.2, and the mean paint lightness is Mean_p = 70. Raw Change is 1.6. The Granulation Index is 100 × 1.6 / 70 = 2.29. Therefore, the rating is Moderate.

What if the paper texture is exaggerated

Some papers may show an exaggerated fiber texture. To focus on the broader mottling you see at a normal viewing distance, you may apply a slight soft blur before the math. Set the blur strength to two pixels at 1200 dots per inch. That setting reduces fiber‑scale noise yet keeps the larger pattern. Use the same blur on the paint and paper areas.

Turning numbers into categories

Figure 4 — Category gallery. Reference swatches from None to Extreme with their Granulation Index values.

We map the index to these labels using the boundaries as follows:

• None: < 3%

• Slight: 3–7%

• Moderate: 7–12%

• Strong: 12–18%

• Very Strong: 18–26%

• Extreme: > 26%

Because the index is continuous, colors near a boundary can be interpreted differently by different viewers. However, repeat measurements of the same paint under this method cluster within a narrow band.

What matters for contemporary artists

Plan texture instead of chasing surprises

You can select paints for soft, broken skies or for flat, graphic shapes with less trial and error. Additionally, the categories travel well across brands, since the same recipe is used for every color we test.

Paper choice is part of the look

Also, paper plays a role in the effect. Our starting level removal reduces the paper’s role but does not erase it. Therefore, if you change paper, re‑test a favorite color once to learn the new starting level.

Mixes and glazes

Also, low‑granulating colors can wake up when mixed with high‑granulating partners. Conversely, a strongly granulating color can calm down when glazed over a dense underlayer. Because the index is measured at midtone, it correlates well with tinting strength. However, very dark passages reduce change and may look smoother than the number suggests.

Control with water and timing

More water and longer drying times often strengthen granulation. Meanwhile, fast‑drying conditions reduce flow and soften the pattern. Use these levers with intent. The index still shows the paint’s bend, but your technique can nudge the outcome.

Digital capture and reproduction

Scans and prints of granulating washes can look harsher if the sharpening is left on. Therefore, turn off capture sharpen and apply only gentle output sharpen matched to print size. The scale of the pattern matters; too much sharpening creates edges that weren’t there.

The science behind the effect

Particle size and density

Larger or heavier grains settle faster as the water flows. They gather in small dips between fibers. Smaller or lighter grains ride fluid currents longer and even out. Therefore, pigments with wide size spreads often granulate more.

Surface chemistry and clustering

In water with a gum binder, grains carry surface charges. Salts and other additives can screen those charges. When screening is strong, grains can approach each other and form soft clusters. These clusters act like larger bodies and settle unevenly. Gentle clustering is not the same as flocculation, which is runaway clumping in the pan or palette.

Flow within the wash

As water dries, wicking flow drags grains toward drier regions. Edges dry first. Meanwhile, gradients form inside the wash. This internal “micro‑weather” helps build the mottled field we see as granulation.

Paper shape and sizing

Hot‑press cotton paper looks smooth, yet its fiber network has small valleys and plateaus. Sizing on and inside the paper guides how water flows and where the binder sits. Hygroscopicity is the extent to which a material absorbs water from the air and from liquids. Hygroscopic sizing swells when wet and opens short‑lived paths. So, pigments find preferred paths and resting places. Our starting level for paper captures much of this role.

Binder concentration and solid content

Critical pigment volume concentration is the point where there is just enough binder to hold the solids together. Below that point, the film looks smoother. Above it, tiny voids appear, and the texture becomes more apparent. Watercolor washes stay below this point, yet local shifts occur as water leaves. Crosslink density is the degree to which the dried binder network is crosslinked. In a tighter network, flow stops sooner, and the pattern freezes earlier. Therefore, pigment‑to‑water ratio and gum strength matter.

Refractive index and visibility

A pigment sitting in a shallow depression may appear darker because it scatters less light and absorbs more. The refractive index is a measure of how much a substance bends light. The contrast between pigment, binder, and air sets the strength of that effect. With greater contrast, the same physical texture produces a stronger tone signal.

Quality assurance and repeatability

Run two swatches per color and report the average index. If the second copies differ by more than 10%, discard both and remake the pair. Also, keep a log of scanner settings, paper lot, and room conditions. Re‑scan a known “control” swatch at the start of each session. If its index exceeds 10%, check the lighting or settings before you continue.

Using the scale in daily work

Choose paints rated None or Slight for smooth skies, skin, and graphic passages. Choose Moderate to Strong ratings for stone, earth, foliage, or lively atmospheric washes. When a mix must be even, glaze a low‑granulating color over a high‑granulating base rather than mixing them wet. Conversely, for a single-pass texture, mix them in the palette and paint once. Finally, remember that paper still speaks. Retest when you change sheets.

Troubleshooting

• Backruns and blooms: These are separate effects. Avoid them by steering clear of puddles and drafts.

• Staining pigments: Strongly staining colors can read smoother than expected. Consider a slower, wetter wash to reveal their texture.

• Metallic or pearly colors: Their sparkle is directional and not well described by this metric. Treat their ratings as a guide only.

• Very dark swatches: Aim for a gradient with a clear midtone. If the entire swatch is near black, the index will be unfairly low.

• Near the paper baseline: If a swatch’s SD_p is ≤ the paper baseline SD_b, the corrected term becomes zero and GI = 0. That means the visible mottling is indistinguishable from the paper’s own texture under this method. It’s expected for some smooth colors and papers.

How to reproduce this at home with minimal gear

You can perform a simplified version with a modern phone camera. Place the card under bright, even window light. Hold the phone parallel to the surface and disable automatic filters. Photograph the paint area and a blank paper area. Then use a basic editor to view the lightness histogram and judge the spread. Although the numbers will differ from a set scan, the relative ranking of paints will be similar. Therefore, you can still sort colors by granulation tendency.

Recording your results

What this method does not cover

It does not rate sparkle or metallic effects. It does not predict edge darkening or blooms. It focuses on the visible mottling in a stable midtone. Even so, this is the part of granulation that most often shapes the look of skies, rocks, and foliage. Therefore, it is the most useful single number to guide choice.

Notes

1. Whatman 42 is a quantitative, ashless filter paper with the finest particle retention (2.5 µm), making it the world standard for critical gravimetric analysis and sample preparation for instrumental analysis. It is made from high-purity cellulose and is suitable for applications that require filtering extremely fine precipitates.

Watercolor artists often describe a color as staining or non-staining, but what do these terms really mean? At Natural Pigments, we wanted to understand staining more precisely—beyond casual impressions—and to offer data that artists can trust. This article explains how we study staining scientifically while remaining meaningful to painters. It details how we prepare swatches, take measurements, and translate those numbers into the familiar artist labels. We also explore alternative approaches and explain why we chose this quantitative method over others.

Understanding “staining” in watercolor

For artists, staining refers to how strongly a pigment binds to or penetrates the paper fibers and how resistant it is to lifting once dry. High-staining colors are difficult or impossible to remove; low- or non-staining colors can be lifted easily, revealing the paper's white beneath. This usage is consistent across artist literature and manufacturers.

Bruce MacEvoy’s authoritative resource, Handprint, defines staining pigments as those whose particles or dyes embed deeply into paper sizing and fibers, resisting re-wetting and blotting. Winsor & Newton explains the same concept: “Staining colours are those which are difficult to remove once dry; non-staining colours lift easily with a damp brush or sponge.” Daniel Smith likewise classifies its colors from low to high staining, noting that highly staining pigments leave a permanent mark even after repeated lifting. Schmincke’s HORADAM Aquarell line describes staining as color particles penetrating the paper, so they cannot be entirely lifted once dry. All agree that staining means difficulty of lifting.

Historically, artists judged staining by brushing out a color, letting it dry, and then trying to lift a portion with clean water and a soft brush. The results depend on paper type, sizing, drying time, and technique, so qualitative tests vary. Our goal was to preserve that artistic meaning—how much color remains after lifting—while eliminating subjective bias.

Why we developed a numerical system

Visual observation alone cannot reliably compare pigments that differ in depth or hue. A pale green and a dark phthalo blue may appear to lift similarly, but differ significantly in how much color actually remains. To make comparisons fair, we measure relative residual color using a spectrophotometer, following the workflow described below. This approach is more objective yet still reflects the artist’s concept of staining: how much color remains after a standardized lifting process.

We call this value the Residual-Color Index (RCI). It expresses the color remaining after lifting as a percentage of the color in the original wash. The math is simple:

RCI (%) = ΔE(Lift, Paper) ÷ ΔE(Wash, Paper) × 100

Here, ΔE is the color difference in CIE Lab* space measured by the spectrophotometer. An RCI near 0% means the lifted area is close to white paper—non-staining. Near 100%, the lift is almost identical to the original wash—high-staining.

How we prepare our test samples

Our swatches are prepared on Whatman No. 42 filter paper, which provides a consistent, absorbent surface. Filter paper ensures uniform capillary action and minimizes surface texture variations. Each piece measures about 5 × 10 cm. The process follows our internal laboratory procedure for color property evaluation.

We first dilute a measured portion of watercolor paint with distilled water to a fixed paint-to-water ratio. Using a clean 25 mm flat brush, we draw a single, even stroke across the paper at a controlled speed. The wash dries for five minutes before the lifting step begins.

To simulate a controlled lift, we flood a narrow central band with clean water, lay a damp cellulose sponge across it, place a one-kilogram weight on top, and leave it for ten seconds. The sponge is removed and the strip allowed to air-dry. The result is a clear band of lighter color across the wash—identical in preparation for every pigment.

Figure 1 — Preparation of watercolor strips on filter paper. The center band is the area designated for lifting.

Once dry, we record CIE Lab* values for three spots: bare paper, unlifted wash, and lifted area. These readings form the data for calculating the RCI.

Measuring and interpreting results

We compute ΔE—the perceived color difference—between each region. ΔE(Wash, Paper) tells us how far the original wash color is from the paper. ΔE(Lift, Paper) tells us how far the lifted area remains from the paper. Dividing one by the other gives a percentage that represents how much color remains.

For example, if the wash is 80 ΔE units from the paper and the lift is 40 ΔE units away, then RCI = 40 ÷ 80 × 100 = 50%. The lifted area retains half the color difference of the original wash, indicating medium staining.

We assign labels based on the RCI scale:

• Non-staining: less than 30 %

• Low staining: 30–55 %

• Medium staining: 55–75 %

• High staining: above 75 %

These ranges translate numerical data into terms artists understand. A high-staining pigment resists lifting, showing only a slight change between the wash and lift. A low-staining pigment shows a significant change—the color nearly disappears.

Preparing paper for better lifting tests

Not all papers lift color the same way. Sizing and absorbency are crucial. For artists wanting to prevent staining and lifting, a well-sized surface helps keep water out. We recommend using a traditional natural-resin varnish, such as Rublev Colours Lac Water Varnish, to lightly seal the paper. This thin varnish is brushed on, creating a less absorbent surface that more closely resembles an external-sized watercolor sheet and produces more consistent lifting behavior. When applied evenly and allowed to dry thoroughly, it prevents excessive pigment penetration and makes lifting reproducible across sessions.

Why this numerical method matters

Our method turns a subjective judgment into a repeatable measurement. Because the Residual-Color Index normalizes for the initial strength of the wash, it allows comparison between very different pigments. Artists can see that a pale yellow and a deep blue are both “low-staining” for the same physical reason: both lose most of their color difference relative to paper after lifting.

Manufacturers and artists describe staining qualitatively, but those descriptions rest on the same foundation—resistance to lifting. The RCI expresses it as a ratio. For colors like phthalo blue or quinacridone magenta, the lifted band remains close to the wash, giving an RCI above 75% and a high-staining label. For pigments like cobalt yellow (aureolin) or cerulean blue, the lifted band moves much closer to white paper, yielding an RCI below 30% and a non-staining label.

Figure 2 — Examples of swatches showing Non-staining, Medium, and High-staining behavior after identical lifting cycles.

This system aligns with definitions used by Winsor & Newton, Daniel Smith, and Schmincke, but provides a quantitative scale rather than a visual guess. It’s also reproducible: any lab with the same procedure and instrument can replicate the numbers.

Alternate visual labeling—and why we don’t publish it

During early testing, we explored a “visual” rule that combined absolute residue (the ΔE between the lift and paper) with hue-specific adjustments and changes in lightness (ΔL). This approach produced labels that matched visual impressions for some colors—especially yellows and oranges that appear bright even when most pigment has been removed—but it added subjective judgment. Because different hues appear lighter or darker at the same chroma, this rule cannot guarantee cross-color consistency. We therefore keep it as an internal reference but rely on the RCI scale for published results.

Figure 3 — Numeric (RCI) vs. Visual (Hue-Aware) Labeling illustrates how two different methods for classifying watercolor staining can produce slightly different results.

On the left, the green bars represent pigments ranked purely by their Residual-Color Index (RCI%), the quantitative value derived from color-difference measurements. This scale reflects how much of the original color remains after lifting, independent of hue or brightness. Higher RCI % means more color remaining (high-staining), and lower RCI % means most color has lifted (non-staining).

On the right, the red bars show how the same pigments might be judged using a visual or hue-aware approach, which adjusts classifications based on how the color appears to the eye. For example, yellows or light earth colors may look more intense than their measured RCI suggests, so they might be placed higher (more “staining”) in a purely visual system.

The figure demonstrates that while the visual approach can seem intuitive, it introduces inconsistencies between hues. The numeric (RCI) method, though more technical, provides a fair, repeatable comparison across all colors—showing why Natural Pigments chose the RCI-based system for its published staining ratings.

Why we use this method

This approach bridges science and studio practice. It captures what artists mean by staining—resistance to lifting—without depending on human perception of brightness or color memory. The numbers are not abstractions; they describe what painters see when a wash resists the brush and sponge. At the same time, because they are based on repeatable measurements, they allow us to compare colors precisely and publish data that any artist can verify.

When we say a pigment is High-staining, we mean it in both the artist’s and the scientist’s sense: the lifted color remains close to its original wash, difficult to remove, and rich in chroma. When we call it Non-staining, it truly lifts back toward paper white. The Residual-Color Index puts numbers to those familiar experiences.

References

Daniel Smith. “Watercolor for Beginners – Watercolor Properties.” Daniel Smith Artists’ Materials. Accessed October 2025. https://www.danielsmith.com/tutorials/watercolor-for-beginners/

Daniel Smith. “Making Sense of Staining, Sedimentary and Transparent Pigments.” Daniel Smith Artists’ Materials. Accessed October 2025. https://www.danielsmith.com/tutorials/staining-sedimentary-transparent-pigments/

Daniel Smith. “Watercolor Pigment Characteristics – Staining.” Daniel Smith Artists’ Materials. Accessed October 2025. https://www.danielsmith.com/daniel-smith-watercolor-pigment-characteristics-chart/

Holbein Works Ltd. “Artists’ Watercolor.” Holbein Works Ltd. Accessed October 2025. https://www.holbein.co.jp/en/products/watercolor/artists-watercolor.html.

Holbein Works Ltd. “Artists’ Watercolour – Tubes & Sets (Specification listing includes ‘Staining’ values).” Jackson’s Art (product page). Accessed October 2025. https://www.jacksonsart.com/en-us/holbein-artists-watercolour-paint-15ml-neutral-tint (or raw sienna example).

MacEvoy, Bruce. “What the Ratings Mean: St- (Staining) & VR (Value Range).” Handprint. Accessed October 2025. https://www.handprint.com/HP/WCL/pigmt8.html

MacEvoy, Bruce. “Watercolor Palette: Staining.” Handprint. Accessed October 2025. https://www.handprint.com/HP/WCL/palette2.html#staining.

Maimeri. “MaimeriBlu Superior Watercolors – Staining Colors.” ArtMaterialEssentials.com. Accessed October 2025. https://artmaterialessentials.com/maimeri.html.

Natural Pigments Laboratory. Watercolor Properties Evaluation. Willits, CA: Natural Pigments, 2025.

Natural Pigments. “Rublev Colours Lac Water Varnish.” Accessed October 2025. https://www.naturalpigments.com/lac-water-varnish.html.

Schmincke. “HORADAM Aquarell.” Schmincke Website. Accessed October 2025. https://www.schmincke.de/en/products/horadam-aquarell.

Winsor & Newton, “Professional Watercolour – Composition & Permanence Tables,” includes a note: “In water colour, … colours with [staining properties] cannot be lifted completely with a damp sponge and are marked ‘St’.” https://www.winsornewton.com/pages/professional-watercolour

An educational page on their site (“How to lift watercolour”) states: “Non-staining watercolours are likely to settle on the paper after the water has evaporated… once dried, these colours can be lifted off to reveal the white paper beneath them.” https://www.winsornewton.com/blogs/guides/how-to-lift-watercolour

5Barite (also spelled baryte) and its synthetic form, blanc fixe (precipitated barium sulfate), are found in historic and modern oil paints. Artists add it to adjust body, transparency, tinting strength, and sheen. Conservation scientists also use its presence to help date artworks and explain some aging behaviors. This article gathers verified research so you can decide when barite is the right tool in your studio.

Key takeaways for artists

• Barite is highly inert and compatible with drying oils and most pigments (CAMEO, 2022; Eastaugh et al., 2004).

• It lowers tinting strength and hiding power, giving smoother blends and softer chroma without significant oil additions (Eastaugh et al., 2004).

• It usually improves yellowing and oil-bleed control when used moderately in oil paint bodies; however, very high extender loads can give fragile, matte surfaces (Bonaduce et al., 2012; Mayer, 1991).

• Specific mixtures can age poorly under strong light (for example, chrome yellow with sulfate-bearing extenders, and some early cadmium yellow formulations) (Monico et al., 2011; Monico et al., 2013; Monico et al., 2020).

What is barite and blanc fixe?

Barite is the mineral barium sulfate (BaSO₄). Blanc fixe is the fine, precipitated synthetic analogue. Both are white, dense powders with low refractive index relative to oil, so they appear nearly transparent in linseed oil (CAMEO, 2022). Their oil absorption is low compared to chalk, so they add body without demanding much additional binder (Eastaugh et al., 2004).

Historical and modern roles

From the late eighteenth century onward, barite was used as a low-toxicity extender and as part of mixed whites (for example, Venice, Hamburg, and Dutch white), and as a support for organic lake pigments (Eastaugh et al., 2004). In modern practice, it remains a common extender, used with titanium white, or as a bodying filler in colors where handling or gloss needs adjustment (Mayer, 1991; CAMEO, 2022).

Conservation studies frequently report barite in nineteenth-century double grounds, including those used by Vincent van Gogh; the barite often contains natural strontium from celestite, which can fingerprint sources (Marino et al., 2006; Janssens et al., 2013; Van Gogh grounds study [verification required]).

Visual and handling effects in oil paint

Barite reduces tinting strength and hiding power, allowing more subtle mixtures and smoother gradations. Because it is hard and fine, small additions can help break pigment agglomerates during grinding and impart a short, buttery feel in paste (Eastaugh et al., 2004). It also tends to lower gloss and produce a more matte surface as loading increases (Mayer, 1991).

Practical upshot: If a color is too strong, too glossy, or too long and stringy, a modest barite addition usually solves it without flooding the paint with oil (Eastaugh et al., 2004; Mayer, 1991).

Stability and aging: the good news and the caveats

Inert by default. Barium sulfate is chemically stable and generally does not participate in oil reactions or form soaps. It does not blacken lead white as sulfur gases do, because it already is a sulfate (CAMEO, 2022; Eastaugh et al., 2004).

Oil yellowing and bleeding. Mock‑ups show that extender pigments can influence yellowing and oil migration. Aging studies of linseed oil reconstructions indicate that appropriate extender use can reduce oil exudation and limit yellowing; however, results vary with formulation, thickness, and light exposure (Bonaduce et al., 2012; Mallégol et al., 2001). Therefore, use moderate loads and favor good drying conditions.

Light‑sensitive mixtures. The most important caution concerns mixtures with certain yellow pigments:

• Chrome yellow (lead chromate). Under light, chrome yellow can reduce to darker chromium(III) species. Studies link faster darkening to paints where chrome yellow coexists with sulfate-rich phases (including barium sulfate) (Monico et al., 2011; Monico et al., 2013). Keep such combinations out of high‑UV light.

• Cadmium yellow (cadmium sulfide). Several teams have reported cadmium sulfate and related products in degraded cadmium yellows. Sulfate-bearing extenders such as blanc fixe may contribute to these pathways in some formulations (Monico et al., 2020; Comelli et al., 2019). Use caution with high loads of blanc fixe in cadmium yellows.

Analytical and dating value

Barite is clearly visible in elemental and imaging analyses (e.g., X‑ray fluorescence mapping and NanoSIMS). Its appearance in grounds and tube colors after the late eighteenth century helps authenticate and date works. Case studies on Van Gogh’s grounds identified barium sulfate with strontium impurities, consistent with natural barite (Marino et al., 2006; Janssens et al., 2013).

When (and when not) to use barite in the studio

Smart uses

• Taming high‑tint colors. Add a small percentage to phthalocyanine blues and greens, quinacridones, or other powerhouse colors to gain control without chalking the color (Eastaugh et al., 2004).

• Softening gloss. Mix into very glossy colors to create a more satin surface (Mayer, 1991).

• Strengthening paste without extra oil. Improve brush handling of oily or long paints while keeping the oil fraction reasonable (Eastaugh et al., 2004).

• As a lake substrate. Use blanc fixe as a substrate when making organic lakes; it is inert and does not shift hue (CAMEO, 2022).

Use caution

• Chrome yellow or cadmium yellow mixes. Limit blanc fixe loads and avoid harsh lighting, as research links sulfate‑bearing environments to specific degradation routes (Monico et al., 2011; Monico et al., 2013; Monico et al., 2020).

• Very high extender loads. Extremely matte, porous surfaces can collect grime and may be mechanically weaker; keep loads moderate and test (Mayer, 1991).

Working methods and simple tests

1. Bench mix first. Start at a 5–10% barite by weight of pigment in the color and test drawdowns at your normal film thickness. Increase gradually if needed (Mayer, 1991).

2. Check mass‑tone and tints. Compare a 1:1 white tint series with and without barite to confirm that the color still lands where you want it chromatically (Eastaugh et al., 2004).

3. Watch gloss and oil exudation. After a week and one month, inspect for surface bleed or hazing. Adjust load or oil type as needed (Bonaduce et al., 2012).

4. Light test sensitive mixtures. If using chrome yellow or cadmium yellow, expose a masked strip to a window for four weeks alongside a control. If darkening or chalking appears, lower the blanc fixe content and consider display limits (Monico et al., 2011; Monico et al., 2020).

Quick comparison: barite versus common extenders

Safety, storage, and disposal

Barium sulfate is considered non‑toxic due to its extreme insolubility. Nevertheless, avoid inhaling dust or ingesting powder. Use a particulate respirator when weighing fine powders, and work under local exhaust if possible. Clean spills with a HEPA vacuum. Do not wash significant quantities down the drain; collect dry waste and dispose of it in accordance with local regulations (NOAA CAMEO Chemicals, n.d.; PubChem, 2025).

Bibliography

Bonaduce, Ilaria, Maria Perla Colombini, Luciana Duce, et al. “New Insights into the Ageing of Linseed Oil Paint Binder.” Applied Physics A 111, no. 1 (2012): 119–127. https://doi.org/10.1007/s00339-012-7467-z.
Annotation: Analytical study of naturally and artificially aged linseed oil reconstructions. Useful for understanding oil migration, yellowing, and binder changes relevant to extender use.

CAMEO. “Barium Sulfate.” Museum of Fine Arts, Boston, last modified May 2, 2022. https://cameo.mfa.org/wiki/Barium_sulfate.
Annotation: Concise, vetted entry covering properties, synonyms (barite, blanc fixe), and typical applications. Good starting point for safety and identification.

Comelli, Daniela, et al. “Degradation of Cadmium Yellow Paint.” Analytical Chemistry 91, no. 10 (2019): 6465–6473. https://doi.org/10.1021/acs.analchem.8b04914.
Annotation: Case‑based spectroscopy on cadmium yellow degradation. Relevant where sulfate phases are present and for assessing extender risks with cadmium colors.

Eastaugh, Nicholas, Valentine Walsh, Tracey Chaplin, and Ruth Siddall. Pigment Compendium: A Dictionary and Optical Microscopy of Historical Pigments. London: Archetype Publications, 2004.
Annotation: Standard reference on historical pigments and extenders, including barite and blanc fixe. Details on names, optical traits, and historical uses.

Janssens, Koen, et al. “The Use of Synchrotron Radiation for the Characterization of Artists’ Pigments and Paintings.” Journal of Analytical Atomic Spectrometry 28, no. 1 (2013): 1–19. https://pubmed.ncbi.nlm.nih.gov/23772661/.
Annotation: Review of synchrotron‑based methods, including X‑ray fluorescence mapping that reveals barite distributions in grounds and paints.

Mallégol, Jacky, Jacques Lemaire, and Jean‑Luc Gardette. “Yellowing of Oil‑Based Paints.” Studies in Conservation 46, no. 2 (2001): 121–131. https://doi.org/10.1179/sic.2001.46.2.121.
Annotation: Classic study on oil yellowing mechanisms and variables. Helps artists contextualize extender choices regarding yellowing.

Marino, Elise, et al. “Imaging TOF‑SIMS and NanoSIMS Studies of Barite–Celestite in a Painting by Van Gogh.” e‑Preservation Science 3 (2006): 11–16. https://www.morana-rtd.com/e-preservationscience/2006/Marino-06-11-06.pdf.
Annotation: Demonstrates identification of barite with strontium in Van Gogh grounds. Shows how extenders inform dating and sourcing.

Mayer, Ralph. The Artist’s Handbook of Materials and Techniques. 5th ed. New York: Viking, 1991. https://www.penguinrandomhouse.com/books/322005/the-artists-handbook-of-materials-and-techniques-by-ralph-mayer/.
Annotation: Practical guidance on extenders, handling, and film properties in artists’ paints. Offers studio‑level context for barite use.

Monico, Letizia, et al. “Degradation Process of Lead Chromate in Paintings by Vincent van Gogh: Part I. Artificially Aged Model Samples.” Analytical Chemistry 83, no. 4 (2011): 1214–1223. https://pubmed.ncbi.nlm.nih.gov/21314201/.
Annotation: Shows how sulfate phases influence chrome yellow darkening under light. Important caution for using sulfate‑bearing extenders with lead chromate.

Monico, Letizia, et al. “Degradation Process of Lead Chromate in Paintings by Vincent van Gogh: Part IV. Artificial Aging of Model Samples of Co‑Precipitates of Lead Chromate and Lead Sulfate.” Analytical Chemistry 85, no. 2 (2013): 860–867. https://pubmed.ncbi.nlm.nih.gov/23051631/.
Annotation: Expands the mechanistic picture of chromate reduction in sulfate‑rich environments; underscores the role extenders can play in mixed systems.

Monico, Letizia, et al. “Probing the Chemistry of Cadmium Sulfide Paints in The Scream by In Situ Noninvasive Techniques.” Science Advances 6, no. 20 (2020): eaba4017. https://pmc.ncbi.nlm.nih.gov/articles/PMC7228759/.
Annotation: Documents cadmium yellow alteration products, including cadmium sulfate. Relevant when blanc fixe is present with cadmium sulfide paints.

NOAA CAMEO Chemicals. “Barium Sulfate.” Accessed October 27, 2025. https://cameochemicals.noaa.gov/report?key=CH25000.
Annotation: Safety and reactivity overview for barium sulfate. Useful for handling, storage, and disposal planning.

PubChem. “Barium Sulfate.” National Center for Biotechnology Information, accessed October 27, 2025. https://pubchem.ncbi.nlm.nih.gov/compound/Barium-Sulfate.
Annotation: Basic chemical data, manufacturing notes for blanc fixe, and identifiers; supports safety and sourcing decisions.

[Van Gogh grounds study: “Van Gogh’s Painting Grounds: An Examination of Barium Sulfate Extender Using Analytical Electron Microscopy.” Authors and year not fully verified; ResearchGate abstract accessed October 27, 2025. Link: https://www.researchgate.net/publication/227071458_Van_Gogh%27s_painting_grounds_An_examination_of_barium_sulphate_extender_using_analytical_electron_microscopy_-_SEMFIBTEMEDX.
Annotation: Frequently cited in technical literature; indicates strontium‑bearing barite in Van Gogh grounds. Include once a stable citation is secured.

Why we did this

Artists need hue information they can rely on. Names like “Prussian Blue” or “Burnt Sienna” carry history, yet they do not always predict how a paint will behave in tints. Therefore, we built a method that starts with controlled swatches and objective measurements, then translates those numbers into artist‑friendly hue categories and warm/cool bias. The result is consistent across brands and batches, and it is anchored in established testing practice rather than marketing language.

From handmade paint swatches to instrument reading

Swatches you can reproduce

We prepare two swatches for every color on the same standard watercolor paper:

• Masstone: a full‑strength application that shows undertone, granulation, and transparency.

• Tint: a uniform wash adjusted to be close to 40% reflectance at the pigment’s maximum absorption (the darkest part of its spectrum). This target keeps the tint in the range that artists actually use while ensuring the instrument can measure it robustly.

Although the lightfastness standard specifies a drawdown on filter paper for formal tests, we use the same reflectance target when making our watercolor‑paper swatches. This keeps our tint data directly comparable to lightfastness panels and eliminates guesswork when you compare paints.

Spectrophotometer setup

We read each swatch with a benchtop spectrophotometer using standard daylight illumination and a 10‑degree observer. The instrument records the spectral reflectance curve and then calculates CIE L*a*b* values:

• L* (lightness) from 0 (black) to 100 (white)

• a* (green to red axis)

• b* (blue to yellow axis)

From a* and b*, we compute two helpful descriptors:

• Hue angle (in degrees):   mapped to 0–360.

• Chroma (saturation):

We average multiple readings if a color has more than one acceptable tint swatch (for example, 36% and 44% reflectance). This smooths paper texture effects and granulation.

How we improve objectivity in the tint range

To remove paper influence and reduce noise where artists actually work (in washes), we apply two steps before assigning warm or cool:

1. Paper compensation. We measure the same sheet of watercolor paper (for this set: L* 95.13, a* −0.09, b* 3.64) and compute Δa* and Δb* for each tint row (swatch minus paper). This subtracts paper warmth and makes brands and batches comparable.

2. Weighted use of many tints. Instead of relying on one tint, we use all rows between 20–70% reflectance and compute a Gaussian‑weighted average centered at 40%. This emphasizes the ASTM tint target while averaging out granulation and application variation. We refer to the resulting Δ value we use in a family as the Warmth_Score, and we report which axis was used (Score_Axis).

Turning numbers into artist‑friendly hue categories

Two questions guide the assignment

1. What is the core hue family? We determine this from masstone appearance and its measured hue angle. The family labels are the familiar artist primaries and secondaries: Red, Orange, Yellow, Green, Blue, Violet, plus Brown and Black/Gray for low‑chroma neutrals.

2. Does the tint lean warm or cool? We answer this with the tint’s a*/b* bias, because artists experience warm/cool shifts most clearly in washes.

The decision rules we apply

We kept the rules simple enough to explain, yet precise enough to reproduce.

A. Hue family (first pass)

• If chroma is very low in masstone, the color enters the neutral families (Black/Gray or Brown) rather than a chromatic family. Otherwise, the hue angle directs it to Red, Orange, Yellow, Green, Blue, or Violet.

B. Warm versus cool (tint‑based)
We use the tint’s sign and magnitude along the a*/b* axes to decide the lean within the chosen family:

These thresholds reflect how painters describe bias in mixtures and washes. They also keep the system legible on category pages and filter swatches.

Why tints, not just masstones?

Painters mix in the tint range. Therefore, a paint’s warm/cool behavior must be interpreted in terms of how water dilutes the film and how paper contributes light. Tints reveal the undertone that masstone can hide. For example, a blue that looks neutral in a dense patch can swing greenish in a wash. Our rules capture that behavior.

Special handling for neutrals and earths

Low‑chroma colors deserve their own logic because small numeric shifts can flip a hue label without reflecting what artists see.

• Black / Gray (near‑neutrals). In tints, the chroma is tiny, so we classify the undertone using paper‑compensated deltas. If Δb* ≥ +1.5 or Δa* ≥ +1.5, we label Black — Warm (a brownish cast). If Δb* ≤ −1.5 or Δa* ≤ −1.5, we label Black — Cool (a bluish or greenish cast). When both deltas are within ±1.5, we present Black — Neutral. These thresholds are high enough to ignore instrument noise yet low enough to catch meaningful undertones in mixes.

• Brown / Earth. Browns live at low‑to‑moderate chroma and sit between orange and yellow at tint. Paper light tends to push b* positive, which can make many browns look cool if you rely only on hue angle. Therefore, we anchor the decision on the red–green cue (Δa*) that artists read in mixtures, and we allow a neutral zone when that cue is essentially zero.

Brown watercolors: an objective way to decide warm vs cool

Browns in watercolor often appear “warm” to the eye because paper light adds yellow, which raises b* and pulls the hue angle toward about 90°. If we categorize warm/cool colors using only the hue angle, many browns appear cool on paper, even when their mixtures feel reddish. To match practical mixing, we center the decision on the red–green axis (a*) and use hue angle only when a* is essentially neutral.

The rule we apply to browns at tint

1. Detect brown at tint when chroma is modest and the hue angle sits in the orange–yellow sector:

   8 ≤ C*ab ≤ 30 and 25° ≤ h° ≤ 110°.

   (We extend the upper bound from 95° to 110° so burnt umbers near yellow still classify as brown.)

2. Warm / cool / neutral split using paper‑compensated Δa*, averaged across many tints with Gaussian weight centered at 40%:

   • Brown — Warm if Δa* ≥ +0.5.

   • Brown — Cool if Δa* ≤ −0.5.

   • Brown — Neutral if −0.5 < Δa* < +0.5.

   We publish Warmth_Score = weighted Δa* so you can gauge how strong the bias is.

This approach privileges the red/green cue artists use when neutralizing flesh, greens, and skies, while dampening paper and application effects through averaging.

Two measured examples

Reconciling names with measurement. Product names follow historical or supplier conventions. Our site labels reflect measured tint behavior because that predicts mixtures. When a legacy name says “Warm” but the tint a* is negative, we list it as Brown — Cool and show the swatch and data so you can judge by eye. When helpful, product pages include a note such as “Measured hue bias: cool.”

What this gives you as an artist

• Transparent filtering: Category pages show hue families you already speak. The warm/cool split helps you pick complements and split primaries quickly.

• Predictable mixing: Because assignments come from the tint range, the buckets predict how a color leans in actual mixes. You can plan secondaries and neutrals with fewer test strips.

• Cross‑brand consistency: The same rules apply to every paint. Therefore, a “cool blue” in our system behaves like a cool blue, regardless of name.

Why perception sometimes disagrees with the label

Language is slippery. “Greenish blue” is Blue—Cool in our rules because a* is negative at tint. However, granulating pigments, optical brighteners in paper, and differences in binders can nudge readings. We average multiple measurements and inspect edge cases, but we always show the measured outcome instead of the marketing name. When your eye says one thing and the label says another, check the warm/cool tag and the sample image; they directly describe tint behavior.

Limitations and transparency

• Paper matters. Watercolor paper tone and sizing influence the tint’s lightness and chroma. We control this by using the same stock for all swatches and by targeting the same reflectance range.

• Granulation and texture can introduce local variation. We average multiple readings and standardize the swatch method to reduce noise.

• Multi‑pigment mixes are classified by their measured tint behavior. If a mixture straddles boundaries, we flag it for manual review and keep the choice most useful to painters.

A quick example: from swatch to hue bucket

1. Prepare a uniform tint wash close to 40% reflectance at the pigment’s absorption minimum.

2. Measure L*a*b*; compute hue angle and chroma.

3. Select a family based on masstone hue (or low‑chroma rules for neutrals).

4. Apply the tint‑bias rule for that family to assign Warm or Cool.

5. For blacks and browns, use the undertone and the specialized thresholds above.

Pocket formulas

• Hue angle: (wrap to 0–360)

• Chroma: 

• Warm/Cool rules: see the table under “The decision rules we apply.”

What matters most for contemporary practice

This approach respects tradition while serving modern workflows. It is reproducible, brand‑agnostic, and sensitive to the part of a paint’s behavior you actually use—the tint. Therefore, you can build split‑primary palettes with confidence, compare earths by undertone, and choose blacks that land the neutral you want without guesswork. Because the system is based on measured tints, the labels on our site reflect what will appear on your paper.

Bibliography

ASTM International. Standard Specification for Artists’ Watercolor Paints (ASTM D5067‑16, reapproved 2021). West Conshohocken, PA: ASTM International, 2016 (reapproved 2021). https://doi.org/10.1520/D5067-16.
Annotation: Defines performance and labeling requirements for artists’ watercolors and the specimen preparation used in lightfastness testing. Its tint drawdown target (approximately the mid‑reflectance range) informed our choice to center measurements around a 40% reflectance tint when assigning hue.

ASTM International. Standard Test Methods for Lightfastness of Colorants Used in Artists’ Materials (ASTM D4303‑10(2022)). West Conshohocken, PA: ASTM International, 2022. https://doi.org/10.1520/D4303-10R22.
Annotation: Specifies exposure regimes and evaluation procedures for rating lightfastness of artists’ media. While our focus here is hue assignment, we mirror its specimen logic so tint data relate meaningfully to permanence evaluations.

International Organization for Standardization; Commission Internationale de l’Éclairage. ISO/CIE 11664‑4:2019 Colorimetry — Part 4: CIE 1976 Lab colour space.* Geneva/Vienna: ISO and CIE, 2019. https://www.iso.org/standard/74166.html.
Annotation: Establishes the definition of the CIE 1976 Lab* colour space that we use to compute a*, b*, chroma, and hue angle from spectrophotometer readings of our tints.

Commission Internationale de l’Éclairage (CIE). CIE 015:2018 Colorimetry, 4th ed. Vienna: CIE, 2018. https://cie.co.at/publications/colorimetry-4th-edition.
Annotation: Authoritative reference for observers, illuminants, and recommended practice in color measurement. We follow these recommendations when selecting instrument geometry and the standard observer/illuminant for our measurements.

 Artist Review of Caroline Magnain’s “Modélisation de la couleur de la peau et sa représentation dans les œuvres d’art” (Modeling skin color and its representation in artwork)

The article explains, in practical terms, how skin and paint handle light—and why that matters when painting skin tones. The author Caroline Magnain developed a detailed skin model and validated it using real measurements in “Modélisation de la couleur de la peau et sa représentation dans les œuvres d’art” (Modeling skin color and its representation in artwork) [p. 62]. The collaborators then tested painted panels made with five binders and earth-color mixtures to see how the choice of medium affects gloss, value, and color. The takeaways are directly useful at the easel: choose a binder to set sheen and depth; know when titanium white will flatten differences and when lead white preserves nuance; plan underpainting, scumbles, and glazes that behave predictably; and match your ground and final finish to control glare. This article translates those results into plain, step‑by‑step guidance you can apply right away.

Key Takeaways

• A 22‑layer skin model fits real data. Three parameters primarily drive most color changes: melanin, blood volume, and oxygenation [pp. 59–62].

• The binder sets gloss. Water‑based binders dry matte. Safflower oil dries to a glossy finish [pp. 125–129].

• Color strength depends on the refractive index gap between pigment and binder. Lower‑index binders look lighter at the same load [pp. 136–141].

• Titanium white pushes reflectance toward 1 and maximizes opacity, but can hide binder differences. Lead white, on the other hand, lifts value more gently and preserves surface character in tints [pp. 139–141].

• Kubelka–Munk lets us compare paints fairly by extracting absorption (k) and scattering (s) from reflectance [pp. 113–121].

Figure 1: Layers of human skin—epidermis (with stratum corneum) and dermis over hypodermis. The thin surface envelope (sebum + stratum corneum) produces the small specular highlight; deeper layers scatter and absorb light, shaping hue and value. This layered structure parallels the paint stack discussed in the article.
Credit: OpenStax, Anatomy & Physiology 2e, CC BY 4.0. Source: https://openstax.org/books/anatomy-and-physiology-2e/pages/5-1-layers-of-the-skin

How the research informs artists about painting skin tones

Optical model of skin

The model treats skin as a 22‑layer structure spanning the epidermis, dermis, and hypodermis, with each layer populated by its principal scatterers—melanosomes, keratin, collagen, and red blood cells. Using the auxiliary‑function solution to the radiative transfer equation, the authors fit the model to measured skin spectra and obtained close agreement. They then varied melanin, blood content, and blood oxygenation to observe how each parameter shifts the spectrum and, therefore, the perceived hue and value [p. 62]. For painters, the takeaway is direct: subtle changes in layered content produce predictable shifts on the canvas.

From skin to painted flesh

When painting skin tones, the palette for flesh tones has remained remarkably stable—earth reds and ochres, vermilion, lead white, with green earth for cool shadows—techniques have evolved from encaustic and tempera to drying oils and, more recently, aqueous synthetics. Two paintings that use similar pigments can look very different because the binder and the surface texture it leaves strongly influence the final appearance [pp. 93–102].

Binder experiments

To test these effects, the study prepared controlled panels with five binders—cellulosic size, wax milk, Caparol “acrylic” (a vinyl acetate–ethylene emulsion representative of VAE/PVA wall paints), egg tempera, and safflower oil—and four pigment sets: burnt umber (), red ochre (), and each of those mixed with titanium white. Surface behavior was measured using optical coherence tomography, goniophotometry, and gloss at angles of 20°, 60°, and 75°, while color within the film volume was assessed by diffuse reflectance. The Kubelka–Munk method provided absorption (k) and scattering (s) coefficients, allowing for fair comparisons among films of slightly different thicknesses [pp. 102, 104–121]. These measurements directly inform painting skin tones.

Water in aqueous‑borne binders evaporates quickly. Vinyl acetate–ethylene (VAE) and polyvinyl acetate (PVAc) emulsions (e.g., the Caparol paint used in the study) typically leave more open‑pored, matte surfaces because pigment is less encapsulated. By contrast, artist-grade acrylic polymer dispersions coalesce into a continuous film that envelops pigment particles, slightly leveling the surface texture and producing a visual effect closer to oil, although still less glossy than drying oils. Safflower oil forms a continuous film that levels the surface, so passages appear glossier. As a result, gloss trends highest with oil, lowest with aqueous binders, and is in between with egg tempera [pp. 125–129].

Inside the film volume, binders with a lower refractive index reflect more light, so mixtures appear lighter at the same pigment volume. Oil‑bound films, which have a higher refractive index, tend to look slightly darker at equal loading. The exact ordering still depends on pigment type and final dry thickness [pp. 136–141].

Adding titanium white alters this balance. Because titanium white scatters strongly, it drives overall reflectance upward and can mute differences among binders. Even so, oil‑bound mixtures often remain slightly darker in reflectance [pp. 139–141]. Lead white (basic lead carbonate) behaves differently in tints: its lower refractive index (≈1.9–2.0) compared with titanium dioxide (≈2.7) produces gentler scattering, so mixtures raise value without the chalky flattening common with titanium white. As a result, lead‑white tints usually maintain subtle color shifts and surface character, which helps when modeling flesh and preserving binder effects.

Practical applications for painting skin tones

Choose a binder to fit the passage

• When painting skin tones, keep light areas matte for clear form. Use casein or egg tempera for thin underpainting layers (dead color) beneath oil or in passages that remain independent; casein provides a toothier surface, while egg tempera offers a slightly smoother, tighter film. (Vinyl acetate–ethylene or polyvinyl acetate wall‑paint emulsions, like the Caparol test paint, tend to dry even more matte and open‑pored and are not a substitute for artist paints.) Expect lighter tints at the same load because of the lower refractive index and the rougher surface [pp. 136–141].

• Deep, glossy halftones. Use drying oil when you want depth and flow. Oil reduces surface scatter and raises gloss. It also lowers reflectance, so halftones look richer [pp. 125–129, 136–141].

• Temper the middle. Egg tempera sits between the two. It can be slightly glossier and slightly darker than casein, yet still holds edges [pp. 136–141].

Pair pigments and binders on purpose

• When painting skin tones, earths change more in gloss than in hue across binders. Oil appears smoother and slightly darker. Casein and VAE/PVA emulsions appear lighter and slightly duller at the same load, whereas artist-grade acrylic dispersion typically falls between oil and these aqueous systems [pp. 128–141].

• White mixtures. When painting skin tones, titanium white can mask binder effects and increase glare. Lead white (basic lead carbonate) has a lower refractive index (≈1.9–2.0) than titanium dioxide (≈2.7), so tints rise in value more gently and preserve subtle hue shifts and surface character. When a mixture contains a lot of white, set sheen with the ground’s absorbency (more absorbent gesso → matte; less‑absorbent oil ground → glossier) and with the final finish (matte/satin/gloss varnish—or none), refer to the Safety Notes for guidance on handling and disposal of lead compounds.

Figure 2 (paper Fig. 2.22): Diffuse-reflectance spectra of burnt umber with different binders. Binder choice changes color: diffuse-reflectance spectra of burnt umber for painting skin tones. Oil-bound films exhibit lower reflectance (a deeper tone), while aqueous-bound films appear lighter, confirming how medium selection affects value and sheen.

Build the stack

When painting skin tones, think in layers. Skin and paint are both layered systems, so plan how light will travel through your stack. First block in value with thin, opaque underpainting. Next, establish chroma with lean middle tones. Then adjust hue and surface feel with oil glazes or light‑toned oil scumbles when working over oil layers. Use casein or egg tempera for underpainting layers. Keep layers lean so scattering remains effective [pp. 93–101].

Terminology: scumbles and glazes

• Scumble: a thin, translucent lighter‑colored paint layer brushed over a darker dry passage to lift value and soften edges.

• Glaze: a thin, translucent, darker or more saturated paint layer applied over a lighter dry passage to decrease tonal value or deepen color.
  In this workflow, both are executed in oil over dry oil layers. Aqueous‑borne paints (casein, egg tempera) are reserved for underpainting only.

Science for painting skin tones

• Refractive index. This measures how much a material bends light. A larger gap between pigment and binder means more scatter and lighter tints. Oils have a higher index than water. Water‑based films, therefore, often look lighter at the same pigment volume [pp. 136–141].

• Surface vs. volume scatter. Surface micro‑texture controls gloss. Scatter inside the film sets the reflectance curve that we read as color [pp. 104–113, 128–141].

• Acrylic dispersion vs. VAE/PVA. Artist‑grade acrylic polymer dispersions form films by coalescing polymer spheres around pigment, effectively encapsulating the particles. This reduces surface roughness compared with VAE/PVA emulsions, and the visual result is closer to oil (smoother, slightly darker at equal load) while still drying less glossy than oil. VAE/PVA systems, commonly used in architectural paints, produce more open-pored, matte films.

• Kubelka–Munk (two‑flux). This method utilizes two diffuse light streams: one up and one down. From reflectance, it solves for absorption (k) and scatter (s). This allows you to compare paints without maintaining a constant thickness [pp. 113–121].

• Critical pigment volume concentration. This is the point where just enough binder wets the pigment. Above it, air voids form, surfaces go matte, and color weakens. For most ready‑made tube paints, the pigment volume is already near or slightly below this point. Stay below it for durable films. To achieve matte effects, use casein or egg-tempera underpainting or an oil-compatible matting agent (such as fumed silica, an absorbent ground, or a matte/satin varnish after complete cure) rather than starving the paint and risking underbinding.

• Albedo. The fraction of incoming light a paint layer reflects (by scattering) rather than absorbs; it ranges from 0 (no reflection) to 1 (full reflection). Titanium white raises albedo toward 1, which evens the spectrum and makes different binders look more alike in pale tints [pp. 139–141].

Figure 3 (paper Fig. 2.13): Refractive index of painting binders. Refractive index of painting binders: why oils appear darker and glossier than aqueous films when painting skin tones. The plot compares binder refractive indices across the visible spectrum, explaining lighter tints in low-index films and deeper tones in oils.

Limits of the model and how to read them

Sources of variability in the panels

The panel program isolated binder effects, but some variables are hard to hold constant. Dry film thickness and final pigment volume can change as water, solvents, and oils evaporate or absorb into the ground. Those changes alter micro-roughness and porosity, and appear as a spread in the measurements [pp. 102, 136–141].

What each instrument measures

The instruments emphasize different parts of the film. Gloss at 20°, 60°, and 75° is highly sensitive to slight differences in leveling and surface texture. Optical coherence tomography directly resolves the surface microtopography. Diffuse‑reflectance color measures the combined effects of subsurface scattering and absorption [pp. 104–113, 125–129, 136–141].

Assumptions behind Kubelka–Munk

The Kubelka–Munk approach assumes a uniform, plane‑parallel, sufficiently thick layer under diffuse illumination. When a film is thin, non‑uniform, or strongly forward‑scattering, errors increase. Treat the absorption (k) and scattering (s) values as comparative trend indicators rather than absolute numbers [pp. 113–121].

Pigments and layer design

The pigment set was limited to burnt umber, red ochre, and their mixtures with titanium white. Other pigments—especially organic lakes or high‑index blues—may show different degrees of change across binders [p. 102]. Historical flesh is also a multilayer system, comprising ground, opaque underpaint, translucent glazes, and often varnish. Those additional layers modify both surface and volume scattering beyond what a single‑layer panel can capture [pp. 93–101].

How to apply the trends

When painting skin tones, read the findings as directional. Oil‑bound films usually present higher gloss and slightly lower reflectance; casein or acrylic dispersion tends to dry matte and lighter; egg tempera sits between. Expect the ordering to hold, although exact numbers may vary depending on your ground, thickness, and application method. Always test your mixtures on your ground under your lights before committing to a larger passage [pp. 125–141].

Studio guidance for painting skin tones (step‑by‑step)

1. Decide the sheen for each area. For light passages in the underpainting stage, use casein or egg tempera for thin, matte layers; these keep planes readable. Reserve scumbles (light over dark) and glazes (dark over light) for the oil‑over‑oil stage. Do not apply casein or egg tempera over dried oil layers. For halftones and accents, use oil or a lean resin‑rich medium to build depth and a controlled gloss [pp. 125–129].

2. Pre‑mix two sets of color. For every flesh hue, prepare an oil‑bound version and a casein‑ or egg tempera‑bound version. Test both on your actual ground under D65 standard daylight (~6500 K, the reference light used in color measurement) and under the room lighting where the work will be viewed.

3. Keep mixtures lean, especially in the underlayers. In the block‑in, favor pigment over binder so films stay thin and dry quickly. For later passes, adjust handling with a small amount of medium rather than adding a lot of fresh binder. Avoid solvent‑only washes that can leave underbound pigment, especially since tube oils are already formulated near the critical pigment volume concentration.

4. Use white with restraint. Titanium white is excellent for maximum opacity and a cool, bright (slightly bluish-white) tone, but it can also mask binder differences and increase glare. For tints that rise in value more gently and preserve surface character, consider lead white (basic lead carbonate); its lower refractive index than titanium dioxide keeps subtle hue shifts visible. When you need to raise value without flattening surface character, add small amounts of translucent earths (for example, yellow ochre or Venetian red), or use lead white judiciously, instead of piling on titanium white [pp. 139–141]. Refer to the Safety Notes for guidance on handling and disposal of lead compounds.

5. Plan the layer sequence (“the stack”). First, set the main values with thin, opaque underpainting. Next, place middle tones in thin layers. Where you need to raise value locally over a darker dry passage, use a light‑toned oil scumble; where you need to deepen value or enrich color over a lighter dry passage, use a lean oil glaze [pp. 93–101].

6. Control leveling and texture. Allow oil passages to reach tack‑free before applying lean oil scumbles on top; this keeps the underlying texture intact and helps prevent unwanted sinking.

7. Choose the final finish deliberately. Casein or egg tempera underpainting layers work well beneath oil passages or in self‑contained areas. If you intend to varnish, make a test panel first: varnish fills texture and increases gloss, which may change local value.

8. Watch pigment volume concentration. With most commercial tube paints, the pigment volume is already near or slightly below the critical level. Do not attempt to create matte passages by starving the paint with solvent or by adding excessive amounts of extender. If an area looks chalky or fragile, add a small amount of binder or apply a thin oil glaze to restore cohesion. For a matte appearance over oil paint, use oil-compatible methods: add a small amount of fumed silica or a manufacturer-approved matting medium to the oil paint, adjust the ground to a lower sheen, or choose a matte varnish after the paint has fully cured. Use casein or egg tempera only beneath oil layers, not over them.

Ground, Paint, and Final Picture Finish: A Sheen Matrix

Use this quick matrix to plan surface sheen when painting skin tones. Read across each row as a complete recipe; test on a small panel before committing.

How to use this matrix: Choose the ground to set your baseline sheen, adjust in the paint layer (lead vs titanium; optional matting within oil), then lock it in with the final finish.

Lead White versus Titanium White in Tints

Use this quick selector when choosing a white for painting skin tones and highlights.

Note: Lead compounds require careful handling and disposal—see Safety notes below.

Safety notes

• Lead white and vermilion. Avoid dust. Wear gloves. Keep food away. Rags with oil can self‑heat; dry them flat or store them in a can with water. Follow local disposal rules.

• Acrylic dispersion and casein. Low hazard in normal use. In‑can preservatives and ammonia (present in some acrylics and in certain casein make‑ups) can off‑gas. Ventilate and wear nitrile gloves.

• Egg tempera. Mix fresh. Keep cold if held for a short time. Discard at day’s end.

Comparison: binder behavior with earth pigments

Trends from panels with burnt umber, red ochre, and their titanium mixtures [pp. 125–141].

The science of painting skin tones for artists

Think of painting skin tones as building an optical stack. Choose the binder to set gloss and depth rather than adding more pigments later to force the result. Use titanium white sparingly when you want the surface texture to remain evident. Always test on your ground under your lights; small changes in surface roughness or refractive index can alter the look as much as a color change.

Bibliography

Magnain, Caroline, Mady Elias, and Jean‑Marc Frigerio. “Skin color modeling using the radiative transfer equation solved by the auxiliary function method.” Journal of the Optical Society of America A 24, no. 8 (2007): 2196–2205. https://doi.org/10.1364/JOSAA.24.002196.
Annotation: Builds a 22‑layer skin model and checks it against measured spectra. For artists, it reveals which parts of the skin drive color and why thin, stacked layers yield lifelike results.

Magnain, Caroline, Mady Elias, and Jean‑Marc Frigerio. “Skin color modeling using the radiative transfer equation solved by the auxiliary function method: Inverse problem.” Journal of the Optical Society of America A 25, no. 7 (2008): 1737–1743. https://doi.org/10.1364/JOSAA.25.001737.
Annotation: Finds a small set of factors that can explain a skin spectrum and recovers them from a measurement. This supports targeted changes in paint—value, chroma, and translucency—rather than guesswork.

Magnain, Caroline. Modélisation de la couleur de la peau et sa représentation dans les œuvres d’art. PhD thesis, Université Pierre et Marie Curie – Paris 6, 2009. https://theses.fr/2009PA066501.
Annotation: Pairs the skin model with tests on painted panels using five binders and four pigment sets. The binder trends in gloss and lightness map cleanly to oil, tempera, and water‑borne practice in the studio.

Binder Reference (Typical Dry‑Film Refractive Index)

Note: Values are approximate for transparent films at a wavelength of 589 nm (sodium D). Paint films include pigments and fillers that modify effective RI; emulsions evolve as water/solvent evaporates.

Glossary: Optics Terms for Painters

Couch (optional intermediate layer). A very thin, wiped film of bodied linseed oil used on a dry underlayer to even absorbency and improve leveling before glazing. Preferred to resin interlayers; apply sparingly.

Critical pigment volume concentration (CPVC). The PVC at which there is just enough binder to fill voids between particles.

• Below CPVC: films are denser, glossier, and stronger.
• Above CPVC: films become more porous and matte with reduced strength; appearance can shift even if PVC is unchanged.

Diffuse reflectance (hemispherical). Light reflected in many directions, captured with an integrating‑sphere spectrophotometer. In SCE (specular-excluded) mode, it includes both surface-diffuse (from microtexture) and subsurface/body-diffuse (from scattering within the film).

Holdout. The ability of a paint layer or ground to prevent the binder from soaking in. Good holdout keeps more binder at the surface, improving leveling and specular reflection without adding excessive free oil to the paint film.

Integrating sphere. A coated hollow sphere that collects reflected light from all directions to report hemispherical quantities. SCI = specular included; SCE = specular excluded.

Kubelka–Munk (K, S). A two‑flux model that relates diffuse reflectance to absorption (K) and scattering (S) coefficients of a paint layer.

Pigment volume concentration (PVC). Volume percentage of pigment + extenders in the total non‑volatile portion of paint: pigment ÷ (pigment + binder). Solvent and driers excluded.

Refractive index (RI). How strongly a medium bends light. High‑RI pigments in lower‑RI binders increase scattering; lower contrast reduces scattering and deepens appearance.

SCI/SCE. Instrument settings for integrating‑sphere measurements: SCI collects both diffuse and specular; SCE excludes the specular component to emphasize the diffuse lobe.

Specular reflection (gloss). Mirror‑like reflection from the paint surface; responsible for highlights. Measured with gloss meters or angle‑resolved setups.

Subsurface (body) scattering. Scattering that occurs within the paint layer as light interacts with pigment particles and pores.

Surface‑diffuse scattering. Diffuse reflection caused by microtexture at the paint surface that breaks up the mirror component.

Transmittance. Light that passes through a substance, such as a paint film.

Varnish (final topcoat). A removable protective coating applied after adequate curing. Not a painting medium; do not add varnish resins (e.g., damar/Maroger) into the oil paint film.

Viewing‑angle effects (angle‑dependent reflectance). Changes in appearance with observation angle, governed by the bidirectional distribution of reflected light (specular vs. diffuse) and surface micro‑roughness; measured with angle‑resolved geometries.

Labor Day in the studio is more than a long weekend; it’s a moment to consider how artists have pictured the dignity, skill, and everyday reality of work. The paintings below—spanning domestic tasks, factory floors, open markets, harvest fields, and public speech—show labor as central to human life. They also offer useful lessons in composition, palette, and technique for today’s painters.

Ben Shahn, Freedom of Speech (study for a Four Freedoms mural) 1941

Shahn, a Social Realist, used drawings and studies to probe composition and message. In this study, the “work” is civic: a citizen speaking, faces listening. Structural diagonals and value grouping lead the eye through hands, mouths, and paper—tools of democratic labor. The simplified shapes are deliberate, supporting clarity over flourish.

Ideas for the Studio

Establish the image as a pattern of values before pursuing the details. Mass the listeners into a single mid-tone shape and hold your strongest contrast for the speaker’s face and hands. A toned ground helps you judge the middle quickly; draw or block in the diagonals that lead the eye through paper, gesture, and gaze. Keep shapes simplified and edges deliberate so the composition reads with the clarity Shahn prized.

Technique Notes: How Painters Picture Work

Begin with value structure, not color. Labor is read through action—hands engaged, bodies bent to a task—and those actions only register cleanly when the scene is organized into clear value groups. If the mid-tones hold together and the darkest darks and lightest lights are reserved for the focal work, the eye will travel naturally to faces, hands, and tools.

Choose a palette that serves material truth rather than spectacle. Earth colors—ochres and umbers moderated by bone or ivory black—mix a wide family of stable neutrals that sit comfortably as skin, cloth, metal, and dust. With this foundation, small calibrations in temperature and saturation become meaningful: a warmer neutral tips a face toward effort and heat; a cooler one settles machinery into shade.

Treat edges as part of the storytelling. Where the human hand meets a tool, firmness in the edge gives weight and clarity; where cloth settles into folds or smoke drifts across a beam, a softened boundary lets the eye rest and implies atmosphere. The alternation between sharp and soft is a quiet rhythm that keeps the narrative legible.

Consider the surface before the first mark. A slightly toothy ground takes broken color beautifully, catching dry-brush passages that suggest fabric nap, straw, grit, or steam without laboring over detail. When the ground supports this kind of varied deposition, you can imply far more than you render.

Use glazing with restraint and intention. Transparent warm layers floated over cooler underpainting can breathe heat into a furnace scene, suggest the humidity of breath in winter air, or lay a film of grime across a wall—yet because the underlying drawing and value remain intact, the form stays solid. Glazes should enrich, not obscure.

Looking at Labor Today

Spend time where work happens—at a farmers’ market in the early morning hours, in a repair shop late in the afternoon, or beside a construction site in the late afternoon—and draw what you see. Notice the signature gestures of each trade: how a hand wraps a knife handle, how a wrist turns a wrench, how a shoulder leans into a sack of feed. Let tools, posture, and light define character before you reach for ornament.

Make small value studies on site, then develop larger paintings in the studio with the same clarity. Choose a vantage point that reveals the task without crowding it, simplify the scene into coherent shapes, and allow a few carefully placed edges and accents to carry the story. When drawing and value do the heavy lifting, the painting honors both the worker and the work.

Part 2 of 2 – Solvent-Free Oil Painting Mediums

Read Part 2 (Alkyds) →

Solvent-Free Oil Mediums—Clear Options for Real Studios

Choose between gels or pastes—no solvents required.

What Artists Say About Solvent-Free Oil Painting Mediums

Oleogel

 

Walnut Oil Gel

 

Epoxide Oil Gel

 

Pale Drying Oil Gel

 

Velázquez Medium

 

Impasto Medium

 

Impasto Putty

 

Part 2 of 2 of the “Solvent‑Free Oil Painting Mediums” series

Why Look Past Alkyd?

Painters seeking faster drying often turn first to solvent-free alkyd gels. Yet many studios want a completely resin‑free approach that still avoids mineral spirits. Modern product lines now offer purified, polymerised, or gelled drying oils that flow well, level predictably, and release almost no volatile organic compounds (VOCs). This article explains how these non‑alkyd alternatives work, compares leading brands, and outlines best practices so artists can adopt them with confidence.

Regulatory Framework for Non‑Alkyd Media

Trace solvents and VOC reporting

Pure or polymerized drying oils are classified as non-hazardous under the OSHA Globally Harmonized System; their Safety Data Sheets list 0% VOC and no flammable-liquid pictogram (Gamblin Artists Colors, 2023). ISO 14021 treats “free‑of” claims as valid when only background residues remain and no solvent is intentionally added (ISO, 2016). Therefore, a fluid or gelled oil sold as “solvent‑free” should disclose only triglycerides, silica, driers, and trace water.

Bio‑esters and the “green solvent” issue

Plant-derived esters, such as those in Sennelier’s Green for Oil line, dissolve paint films but evaporate slowly and exhibit low toxicity (Sennelier, 2024). While the company markets them as safer substitutes for mineral spirits, they still act as solvents and require ventilation. For clarity, this article labels them “solvent‑reduced,” not truly solvent‑free.

Compare Solvent-Free Oil Painting Mediums

Solvent-Free Oil Painting Mediums