Blue Ridge Raw Umber Pigment

Our Blue Ridge Raw Umber is a fine, brown powdered pigment from Virginia, USA. Umbers are mineral pigments that can be used in all mediums, such as tempera, oil, and watercolor, and are obtained from natural earth colored by the oxides of iron and manganese.

Origin and History

Brown earths have been known since prehistoric times and were mentioned in the earliest painting treatises. However, the name umber did not appear until the 16th century. Sixteenth-century Italian painting treatises used the term terra d'ombra, translated as umber for a type of brown earth. The name is likely derived from ombra, Italian for "shadow," because the pigment was useful for dark or shadow areas. Writers of the 17th century mentioned calcining umber before use, and the term burnt umber entered literature around this time. The term raw umber was not commonly used in English treatises before the 19th century. The name umber was frequently used for organic brown pigments in the 18th and 19th centuries, while brown iron oxides were referred to as brown ocher. Today, the name is most often associated with brown earth, composed primarily of iron and manganese oxides. In the 17th century, Turquet de Mayerne made the first association of umber with manganese containing iron oxide pigments by describing the drying properties of umber and the fact the color became brown-red by burning.

Historically, European sources of brown earth (goethite) were mined throughout many regions of Europe. The dark brown umbers, containing 45% to 70% iron oxide and 5% to 20% manganese dioxide, were originally extracted from northern Italy but are now mined primarily in Cyprus. Other sources of umber were found in England, France, Germany, and later in the United States.

Source

Iron oxide earth pigments are an important group of inorganic pigments derived from natural minerals. Iron oxide pigments are yellow, red, and brown, but artists know them as ochre, sienna, red oxide, and umber. Unlike manufactured pigments, 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 these ingredients can combine result in a wide range of possible yellows, reds, and browns.

Principal Coloring Ingredient

Iron oxide is the principal color-producing ingredient on earth. The properties of the particular iron oxide in the earth determine 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 limestone, white clay, and colorless kaolin. Those containing the highest amounts are the rocks from which metallic iron is extracted.

Secondary Coloring Ingredients

Calcite (calcium carbonate), pyrolusite (manganese oxide), and quartz (silica) are some common accessory minerals 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.

Umber is a yellowish-brown to greenish-brown mineral pigment used in tempera, oil, and watercolor, obtained from natural earth colored by iron and manganese oxides. Just as with sienna, the chemical composition of umber is closely related to its iron oxide content. What makes umber different is the increased manganese content. Other substances naturally occurring in umber, include clay, talc, and calcium carbonate, do not affect its color significantly. Umbers with the highest tinting strength are those with the highest iron and manganese content. 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 Russia and Ukraine about 4% manganese.

Source

Our umber, from deposits in the Blue Ridge Mountains of Virginia, USA, is finely ground and exhibits a yellow-brown masstone with warm undertones. It has excellent tinting strength and good covering power.

Tinting Strength

As demonstrated in experiments conducted by K.I. Tolstikhinoy, the chromaticity of natural iron oxide and clay pigments are closely related to the iron oxide content 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%, and the purity of tone 60-70%. With the content of iron oxide from 22 to 74%, luminosities of tone vary in an 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 an 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 umber causes the hydrated iron oxide to give up water, and the resulting dehydration darkens in shade while its tone intensifies. At temperatures exceeding 300° C, yellow and brown pigments acquire red-brown tones. The most intensive red tones are obtained from calcining goethite at a temperature between 500-600° C. The color change 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 permanent, with medium to excellent tinting strength and high opacity. It does not react with solvents and is indifferent to alkalis, but it is partially soluble in acids.

Oil Absorption and Grinding

When dispersed in oil, umber absorbs a moderately high amount of this medium. The oil absorption ratio is 45–55 parts by weight of linseed oil to 100 parts by weight of pigment. If the measurement were grams, umber would require 45 to 55 grams of linseed oil to grind 100 grams 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.