The Role of Oil Painting Driers: A Selection Guide for Artists

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Metallic driers, also known as siccatives, play a fundamental role in oil painting. They catalyze the oxidation of oil binders, accelerating drying times and influencing the long-term stability of the paint film. Historically, artists have employed a variety of driers to control the working properties of their materials. Notable artists such as Rembrandt are known to have used lead-based driers to enhance the drying time and durability of their works. In the 19th century, painters like J.M.W. Turner and John Constable experimented with siccatives to accelerate drying while maintaining flexibility in their paint films. Today, modern formulations provide safer and more efficient alternatives, such as zirconium-based driers, Japan driers, and commercial blends that combine multiple metal salts to optimize drying rates.

This article explores the chemistry, history, and application of metallic driers in oil painting. Understanding the differences between these driers is crucial for contemporary artists, as proper selection and use can impact drying time, paint film integrity, and long-term artwork preservation. By grasping how these driers function, artists can make informed choices that enhance both their painting process and the durability of their works. It categorizes driers into primary, secondary, auxiliary, and commercial types, examining their effects on paint films. It also provides best practices for contemporary painters seeking to optimize drying while preserving film integrity.

The Effect of Driers on Oil Paint

Driers facilitate the oxidative polymerization of drying oils such as linseed, walnut, and poppy seed oil. Different oils react uniquely with driers; linseed oil, which has a high content of polyunsaturated fatty acids, responds well to most driers and dries relatively quickly. Walnut oil dries more slowly but benefits from the addition of cobalt or manganese-based driers. Poppy seed oil, which has lower reactivity with oxygen, is best paired with strong oxidative driers like cobalt and zirconium to improve drying performance. Understanding these combinations helps artists control drying times and the final texture of their work. When oil is exposed to air, it absorbs oxygen, forming hydroperoxides that decompose into radicals. These radicals initiate cross-linking, transforming liquid oil into a solid film.

Without driers, this process occurs naturally but at a slow rate. For instance, raw linseed oil can take a week more to dry, while walnut oil dries slower. Poppy seed oil, favored for its minimal yellowing, dries even more slowly. The introduction of driers can significantly reduce these drying times, allowing artists greater control over their painting process. However, excessive use can lead to embrittlement, surface wrinkling, or discoloration over time.

Historical Use of Driers in Oil Painting

Since the Renaissance, artists have experimented with additives to enhance drying. However, the use of driers in oil painting predates this period. Evidence from medieval European manuscripts indicates the use of lead and manganese compounds to speed up the drying process of oil-based pigments. By the 15th century, Venetian painters were known to incorporate lead-rich drying oils into their works to create durable paint films. Over time, artists refined these methods, developing recipes that balanced drying speed with paint stability. Early manuscripts mention lead oxides, manganese compounds, and zinc vitriol (zinc sulfate ZnSO₄) as effective siccatives.

By the 19th century, British artists commonly used lead-based driers mixed with linseed oil to accelerate drying while maintaining flexibility (Carlyle, 1999). This practice was particularly evident in the works of J.M.W. Turner, who is known for his rapidly executed oil paintings. The use of lead-based driers allowed Turner to work quickly, layering glazes and impastos with minimal waiting time between applications. Similarly, John Constable employed siccatives to enhance the drying speed of his richly textured landscapes, ensuring a more efficient working process. While these driers contributed to their artistic techniques, conservation studies have shown that lead-based drying agents can cause long-term issues such as cracking and brittleness in historical paintings.

In the 20th century, environmental and health concerns led to the decline of lead driers. Safer alternatives, such as cobalt and zirconium, replaced toxic compounds while maintaining drying efficiency (Tumosa and Mecklenburg). Today, conservation science continues to evaluate the long-term stability of drier-modified paints.

Historical Driers: Siccatif de Courtrai and Siccatif de Harlem

Two historically significant driers, Siccatif de Courtrai and Siccatif de Harlem, were widely used by artists in the late 19th century to manipulate drying times. Technically, these were mediums rather than driers since they contained more than simply metallic diers. The composition of these mediums was often secretive and varied depending on the manufacturer.

Siccatif de Courtrai was favored for its rapid drying properties, making it particularly useful for artists who worked in layers and required quick recoating. However, due to its high lead content, it posed significant risks to the stability of the paint film, potentially leading to cracking over time. Conversely, Siccatif de Harlem, being resin-based, was preferred by artists seeking a controlled drying process that resulted in a glossy, hard finish. It was often used in glazing techniques, enhancing luminosity while preserving flexibility in multi-layered paintings. These mediums significantly influenced oil painting methods, enabling experimentation with layering and textural effects.

Siccatif de Courtrai was described as a highly potent and fast-acting drier. However, it was considered dangerous due to its high lead content. Some sources cautioned against its use, warning that it was “heavily loaded with compounds of lead” (Church, 1901, 111). Vibert (1892, 83) also considered it hazardous because it contained turpentine and was often used like a diluent, leading artists to apply excessive amounts. Despite these risks, it was widely employed to accelerate the drying of oil paints, particularly in situations where rapid working times were needed.

Siccatif de Harlem, in contrast, was based on copal resin rather than metallic driers. According to Vibert (1892), it contained oil of spike combined with copal and functioned as both a medium and a varnish. This drier produced a hard, brilliant, and tough paint film, making it useful for artists who wanted to enhance durability and gloss. Unlike true siccatives, Siccatif de Harlem did not contribute oxygen to the drying process; instead, it appeared to speed up drying through its evaporation. A catalog from Lechertier, Barbe & Co. (1879) describes it as being similar to a painting medium rather than a traditional drier. While its effectiveness as a drying agent was debated, it remained popular for its aesthetic qualities.

Modern equivalents of these driers no longer rely on lead or turpentine-based formulations. Instead, safer alternatives like calcium, zirconium, and synthetic resins are used to achieve similar results while minimizing health risks (Carlyle, 1999).

Modern Equivalents of Siccatif de Courtrai and Siccatif de Harlem

Modern equivalents of Siccatif de Courtrai and Siccatif de Harlem have been reformulated to eliminate toxic substances like lead and turpentine while preserving their functionality.

• Siccatif de Courtrai (modern): Today’s formulations avoid lead compounds and instead use less-toxic metal driers such as zirconium and calcium salts. These maintain their function as a through drier, promoting polymerization while reducing the risk of excessive brittleness.
• Siccatif de Harlem (modern): Modern substitutes for Siccatif de Harlem continue to rely on synthetic resins and essential oils rather than metallic siccatives. Current formulations use copal or alkyd-based resins to replicate its hardening effect while ensuring better paint film stability and environmental safety.

These modern versions aim to balance historical working properties with contemporary health and environmental standards, making them more suitable for long-term use by artists and conservators. Instead, safer alternatives like calcium, zirconium, and synthetic resins are used to achieve similar results while minimizing health risks (Carlyle, 1999).

Types of Driers

Primary Driers

Primary driers, or oxidation catalysts, are the most active type of siccatives. They accelerate the initial uptake of oxygen, leading to rapid surface drying. The most common primary driers include:

• Cobalt: Highly effective in catalyzing oxidation but can cause surface wrinkling if overused (Van Gorkum and Bouwman, 2005).
• Manganese: Acts as both a surface and through drier, offering a more balanced drying process than cobalt (Painting Best Practices).
• Iron: Less common in fine art painting but used in industrial coatings due to its red hue and moderate drying capabilities (SpecialChem).

Secondary Driers

Secondary driers work in conjunction with primary driers by promoting oxidation throughout the entire paint layer rather than just at the surface. By ensuring both surface and in-depth oxidation, secondary driers improve the durability and consistency of the paint film. They work alongside primary driers to create a more controlled and uniform drying process, reducing risks such as surface skinning and uneven curing. While primary driers initiate surface drying, secondary driers ensure that the oxidation process continues deeper into the paint film, leading to a more even and thorough cure. These driers help prevent surface skinning, which can trap uncured paint underneath, causing long-term stability issues. Examples include:

• Zirconium: A widely accepted modern replacement for lead, it enhances through drying and does not significantly alter the paint color (Painting Best Practices).
• Barium: Primarily used in industrial coatings, barium helps to improve flow and leveling properties while supporting deeper oxidation (SpecialChem).
• Lead (historical): Previously the standard for through drying, lead is now largely phased out due to toxicity concerns (Tumosa and Mecklenburg).

Auxiliary Driers

Auxiliary driers complement primary and secondary driers by enhancing specific paint properties such as flexibility, gloss, and hardness. While primary driers accelerate surface drying and secondary driers promote through drying, auxiliary driers help fine-tune the drying process to prevent defects such as wrinkling, brittleness, or uneven curing.

Auxiliary driers also modify drying characteristics and other paint properties, such as improving pigment wetting and dispersion and preventing loss of drying properties during storage. These include:

• Calcium: Enhances film hardness and prevents excessive brittleness (Zumbühl and Zindel, 2016). Calcium driers act as effective pigment-wetting and dispersing agents in commercial paint formulations, ensuring a uniform distribution of pigments within the binder. They also function as loss-of-dry inhibitors, preventing the premature drying of paint during storage. Calcium driers are most effective when used in conjunction with primary driers like cobalt or manganese. While primary driers catalyze the surface drying of the paint film, calcium driers support the through-drying process, ensuring that the entire film cures uniformly.
• Zinc: Prevents surface wrinkling and improves gloss but may cause embrittlement in aged paint films (Painting Best Practices).
• Strontium: A relatively new auxiliary drier, strontium provides similar benefits to calcium and barium but with improved environmental stability (SpecialChem).

Commercial Driers

Unlike primary, secondary, and auxiliary driers, which are typically single-metal siccatives used to target specific stages of oxidation, commercial driers are pre-formulated solutions designed to optimize drying performance by combining multiple metal salts. These products are widely available from art supply manufacturers and coatings producers, allowing artists to control drying times and paint film characteristics.

Commercial driers are pre-formulated solutions designed to optimize drying performance by combining multiple metal salts. These are widely available for artists and coatings manufacturers.

• Courtrai Drier (modern): Contains calcium and zirconium salts, improving in-depth drying and balancing drying rates across pigments (Sennelier Artist Materials).
• Japan Drier (modern): A reformulation of traditional lead- and manganese-based driers. Some are reformulated with alkyd resins, others contain zirconium driers, and some do not provide any details of their contents, making them difficult for artists to use. Today, many commercial Japan driers are labeled for use in crafta and gilding applications rather than fine art (Natural Pigments).
• White Drier: A clear, non-yellowing drier with calcium salts that activate pigment drying while maintaining color purity (Sennelier Artist Materials).
• Mixed-Metal Driers: Artist materials manufacturers often offer formulations that combine cobalt and zirconium or manganese and zirconium, improving consistency and reducing environmental impact.

The Importance of Proper Drier Dosing: Myths and Best Practices

Driers play a critical role in oil painting, ensuring that paint films cure at a controlled pace. However, their use is a delicate balancing act—too little, and the paint remains tacky for weeks; too much, and the film becomes brittle, discolored, or prone to cracking (Mallégol, Gardette, & Lemaire, 2012). Misconceptions about drier dosage often lead to unintended consequences that compromise the longevity and stability of an artwork. Understanding the chemistry behind driers ensures optimal workability while preserving the structural integrity of an oil painting over time.

More Is Not Always Better

A common misconception is that adding more drier will proportionally accelerate drying. This belief likely stems from the assumption that increasing the catalyst will always speed up the reaction. However, in the case of oil paint, the oxidation process is highly dependent on controlled exposure to oxygen, and an excess of driers can create surface skinning that traps uncured oil beneath, ultimately slowing the drying process. In reality, excessive use can have the opposite effect, slowing down the overall curing process. This paradox arises because driers do not simply “evaporate” like solvents; instead, they catalyze the oxidation of oil, triggering a complex chain reaction (Just Paint, 2023). When drier concentrations exceed recommended levels, the initial oxidation rate becomes too aggressive, forming a dense, rapidly skinned-over surface. This hardened outer layer prevents oxygen from penetrating deeper into the paint film, trapping uncured oil beneath. As a result, the lower layers remain soft and prone to delayed drying, leading to wrinkling, uneven film formation, and long-term instability (Mallégol et al., 2012).

Research on cobalt and manganese driers has shown that even slight variations in concentration significantly alter oxidation rates. Overloading primary driers like cobalt speeds up surface oxidation but does not necessarily lead to uniform drying throughout the paint layer. This imbalance creates stress within the film, increasing the likelihood of premature cracking and embrittlement as the layers dry at different rates (Just Paint, 2023).

Understanding the Role of Driers in Oxidation

Unlike solvents that disappear through evaporation, driers work by accelerating oxidation—a chemical reaction that hardens oil by linking molecules into a stable, polymerized structure. However, excessive oxidative stress can disrupt this network. Studies on the long-term behavior of oil-based varnishes and paints reveal that an overabundance of driers leads to chain scission, a breakdown of molecular bonds that weakens the paint film (Mallégol et al., 2012). Instead of forming a durable and flexible structure, an over-dried film becomes brittle, making it prone to flaking and irreversible degradation over time.

Additionally, an excess of certain metal driers, particularly cobalt, accelerates the depletion of antioxidants in the oil, increasing the risk of premature yellowing and photodegradation (Just Paint, 2023). Antioxidants play a crucial role in slowing the oxidation process, preventing the oil from becoming overly brittle and yellowed over time. When antioxidants are depleted too quickly, the paint film is left vulnerable to accelerated aging, reducing durability and color stability. Over time, the cured paint loses its elasticity, leading to surface failures that compromise both aesthetic and structural integrity.

Best Practices for Dosing Driers

To ensure stable, predictable drying without compromising the longevity of the paint film, artists should follow these best practices:

• Use driers sparingly: Follow the manufacturer’s recommendations, usually provided as the weight percentage of metallic drier per weight of the oil. A general recommendation is between 0.1% and 0.5% drier per weight of oil, depending on the formulation and oil type (Just Paint, 2023).
• Mix driers thoroughly: Uneven distribution can lead to patchy drying, causing inconsistencies across the painting. Mix the drier into the medium or paint with a palette knife to ensure even distribution. Better yet, add the drier to oil and then add the oil to your paint.
• Consider pigment influence: Some pigments, such as lead white and umbers, naturally promote drying and require little to no additional drier.
• Balance with secondary driers: Cobalt accelerates surface oxidation, while secondary driers like zirconium ensure that deeper layers cure evenly (Mallégol et al., 2012).

By carefully measuring and incorporating driers in moderation, artists can achieve optimal drying times without sacrificing the durability of their work. A well-balanced approach to drier use results in flexible, resilient, and vibrant oil paintings that stand the test of time.

Understanding the Role of Driers in Contemporary Oil Painting

Understanding the role of driers in oil painting is essential for artists who wish to balance drying speed, paint film integrity, and long-term artwork preservation. From historical lead-based siccatives to modern, safer alternatives, driers have shaped artistic techniques for centuries. Selecting the right drier requires consideration of the medium, pigments, and desired working properties, ensuring that artists can achieve their creative goals while maintaining the durability of their works. As research in materials science continues, newer, more stable, and environmentally friendly driers will further refine painting practices, offering future generations of artists greater control over their materials.

Historical and Modern Metallic Driers

The dosage recommendation is based on the weight of the metallic drier as a percentage of the total weight of the oil. The manufacturer provides the weight of the metallic drier as a percentage of the total drier, such as Cobalt 20%. These percentages are based on manufacturer's data and are starting points for ladder testing.

Siccatif de Courtrai: History, Composition, and Use in Traditional Painting

A Controversial Yet Powerful Drying Agent

Siccatif de Courtrai, widely used in 19th-century European painting studios, remains one of the most debated driers in art history. It was not a single, standardized product but rather a term applied to various formulations made by different manufacturers, leading to inconsistencies in quality and performance (Pierre, Renseignements sur les couleurs, 100–101). This variability may have contributed to the drier’s controversial reputation, with some artists warning against its use. In contrast, others, such as Bouguereau, incorporated it into their painting practice with careful moderation.

The core ingredients of Siccatif de Courtrai included linseed oil heated in the presence of litharge (lead monoxide) and manganese salt. This combination made it a highly potent drying agent. However, its deep brown color, likened to “black coffee,” often muddied lighter tones, making it unsuitable for applications where color purity was essential (Pierre, 100–101).

Bouguereau’s Use of Siccatif de Courtrai and Huile Grasse

Bouguereau, known for his meticulous painting technique and controlled drying processes, appears to have used a variation of Siccatif de Courtrai in his mediums. The reference to huile grasse in his notes suggests that he employed either Courtrai drier or a similar lead- and manganese-based siccative oil (Pierre, 89). This oil, produced by heating linseed oil with small amounts of metallic driers, enhanced drying while maintaining flexibility. The presence of huile grasse brune in his formulations further reinforces the connection to Siccatif de Courtrai, as its dark color aligns with historical descriptions of the drier.

Additionally, Bouguereau mentions huile grasse blanche, which was clarified poppy oil treated with lead and manganese compounds. Unlike Courtrai drier, huile grasse blanche retained a pale, milky appearance, making it suitable for use with light-colored pigments and delicate passages where discoloration was a concern (Pierre, 89).

Using Siccatif de Courtrai with Other Driers

Despite its potent drying properties, Siccatif de Courtrai was rarely used in isolation. Artists often combined it with resin-based mediums such as Siccatif de Haarlem or Siccatif Flamand to balance drying effects. These resin-based driers, developed by the pharmacist M. Duroziez, lacked lead but still promoted drying by incorporating copal resin, oil, and turpentine (Pierre, 101–102). The benefit of these mediums lay in their ability to prevent “sinking in,” preserve color vibrancy, and maintain paint film flexibility—features that Siccatif de Courtrai alone could not offer.

Modern equivalents of Siccatif de Courtrai no longer rely on lead and manganese in the same way but incorporate zirconium and calcium-based driers to provide through drying without long-term embrittlement. While today’s alternatives may lack the exact properties of historical formulations, they aim to achieve specific effects while ensuring better stability and safety for artists.

Lessons from History: Moderation is Key

Ludovic Pierre, writing in the late 19th century, acknowledged the risks of Siccatif de Courtrai but emphasized that when used sparingly, it did not necessarily compromise a painting’s longevity (Pierre, 100–101). This aligns with modern research on driers, which warns against overuse due to the potential for embrittlement and surface defects. Historical records from Bouguereau’s practice illustrate that the successful use of driers relied on careful balance, precise formulation, and an understanding of how different siccatives interacted within an oil paint film.

For contemporary artists looking to replicate historical techniques while ensuring long-term stability, a combination of modernized oil-based driers, resin mediums, and controlled drying conditions can provide the best results—without the risks associated with lead-based formulations.

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