Product Details:
100 g jar (3.5 oz)
Our Brown Ochre (Goethite) is from deposits found in the Kaluga region of Russia. Our pigment is finely ground and exhibits a reddish brown masstone. It has excellent tinting strength and good covering power. A yellow to brown mineral, consisting of hydrated iron oxide, geothite is usually present in the oxidized portions of iron ore deposits, and the commonest constituent of many forms of iron oxide.
| Common Names: |
English: brown ochre
French: ocre brun
German: Ocker Braun
Italian: ocra marrone
Japanese: 茶色の黄土色
Spanish: ocre marrón
|
| Mineral Names: |
English: Goethite
French: Goethite
German: Götheit
Italian: Goetite
Japanese: 針鉄鉱
Spanish: Goethita
|
| Alternate Names: |
brown hematite, brown ochre, goethite, yellow ochre (also spelled, ocher)
Mars Yellow and Mars Brown are names given to the artificial substitutes for Goethite. |
Origin and History
Goethite was named for Johann Wolfgang von Goethe (1749-1832), a German philosopher and poet who also was a mineralogist. Goethite has been in continuous use as a pigment since prehistoric times. Evidence of Goethite was found in paint pigment samples taken from the caves of Lascaux, France. In ancient Greece the term "ochre" was used for natural earth pigments of different yellow hues (ochre light, golden, dark, greenish, etc.).
Source
This widespread mineral, consisting of hydrated iron oxide, which is encountered practically everywhere on the earth's surface in the form of concretions, oolites (a form consisting of small round grains cemented together), reniform (kidney shapes) or botryoidal (form of bunches of grapes) accumulations, frequently is encountered in the swampy areas at the head of spring waters, and on the bottom of lakes and small creeks. Iron oxides, or earth pigments, as they often are called, are an important group of inorganic pigments derived from minerals. Iron oxide pigments are yellow, red, brown and green, but artists know them as ochre, sienna, red oxide, umber and terra verte. Unlike pigments made in a laboratory, the color of natural iron oxide pigments varies with the composition of the particular segment of earth from which they come. The color of these pigments is derived from three constituents: the principal coloring ingredient, secondary coloring ingredients and a base. The combination of these ingredients produces the particular color of the earth. The innumerable forms and variations in which these ingredients can combine result in the wide range of possible yellows, reds, browns and greens.
Principal coloring ingredient: Iron oxide is the principal color producing ingredient in the earth. The properties of the particular iron oxide present in the earth determines its color. The nature of the iron oxide found in the deposit, rather than its percentage, is critical to the resulting earth color. Most rock contains some iron oxide. Those bearing the least amounts are limestones. white clays and colorless kaolins. Those containing the highest amounts are the rocks from which metallic iron is extracted.
Secondary coloring ingredients: Calcium, manganese oxide, carbonic materials, silica and limestone are some common modifiers that affect the specific color of natural iron oxides. Manganese oxide, for example, enriches the brown in umbers.
Base: Nearly all iron oxides have a clay base. Clay is the weathered product of silicate rocks and is extremely varied in composition. As a result, it has numerous effects on the earth's color.
A yellowish brown to greenish brown mineral pigment used in tempera, oil and watercolor mediums, obtained from certain natural clays colored by the oxides of iron and manganese. Just as with sienna, the chemical composition of umber is closely related to the iron oxide content of ochre. What makes umber different is the increased content of manganese. Other substances naturally occurring in umber include clay, talc, and calcium carbonate do not affect its color. Umbers with the highest tinting strength are those with the highest content of manganese and iron. Some of the finest umber comes from Cyprus and may contain up to 16% manganese oxide. German umber typically contains 1-2% manganese, English umber 7%, and umber from the Ukraine about 4% manganese.
Our umber is from deposits found in Cyprus. It is roasted to darken the pigment, finely ground and has a reddish-brown masstone. It has excellent tinting strength and good covering power.
Tinting Strength
Relatively large crystals of Goethite give the yellow color of this mineral, whereas smaller crystals produce shades of brown. As demonstrated in experiments conducted by K. I. Tolstikhinoy, the chromacity of natural iron oxide and clay pigments are closely related to the content of iron oxide, and from a mineralogical point of view -- the content of
Goethite. Thus, with the content of iron oxide less than 23%, luminosities of the tone of pigment compose 40-50%, the purity of tone 60-70%. With the content of the iron oxide from 22 to 74%, luminosities of tone varies in interval of 25-40%, the purity of tone from 70 to 85%, and with the content of the iron oxide more than 75%, luminosity is located in interval of 18-25%, the purity of tone 83-90%.
Pigment Characteristics
A characteristic of pigments containing Goethite is their ability to change color when heated. Heating ochre, sienna and umber causes the hydrated iron oxide to give up water, and with the resulting dehydration darken in shade while its tone intensifies. At temperatures exceeding 300°C yellow pigments acquire red-brown tones. The most intensive red tones are obtained as a result of calcining Goethite at a temperature between 500-600°C. The change in color is directly related to the dehydration of Goethite and its transformation into
hematite. Prolonged heating at high temperatures causes another change into a mineral of dark gray color -- magnetite. Roasting umber gives a pigment of black-brown color known as
burnt umber.
Permanence and Compatibility
Umber does not react with other pigments and is effectively used in fresco, oil, tempera and watercolors. It is considered to be permanent with medium to excellent tinting strength and high opacity. It does not react with solvents, and is indifferent to alkalis, but is partially soluble in acids.
Oil Absorption and Grinding
Umber moderately absorbs oil when dispersing it in this medium. The oil absorption ratio is 23–35 parts by weight of pigment to 100 parts by weight of linseed oil. If the measurement were grams, umber would require 100 grams (by weight) of linseed oil to grind 23 to 35 grams (by weight) of pigment to form a stiff paste. Due to its manganese content, umber hastens the drying of oil, and forms a good, flexible film.
Toxicity
Umber is considered non-toxic, however, manganese, a constituent of umber, is considered moderately toxic, so care should be exercised when handling the dry powder pigment so as not to inhale the dust.
Pigment: Brown Ochre (Goethite) (Kaluga, Russia)
| Color: |
Brown |
| Colour Index: |
Pigment Yellow 43 (77492) |
| Chemical Name: |
Iron Oxide Hydrated (partial component) |
| Chemical Name: |
FeO(OH) |
| ASTM Lightfastness Rating |
| Acrylic: |
I |
| Oil: |
I |
| Watercolor: |
I |
| Properties |
| Density: |
3.3–4.3 |
| Hardness: |
5.0–5.5 |
| Refractive Index: |
nα=2.260 nβ=2.393 nγ=2.398 |
Read cautions about handling pigments
Read the Material Safety Data Sheet (MSDS) for this Product
Availability: Usually ships within 24 hours.
