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Sienna, Luberon [100 g jar] (3.5 oz.)
100 g jar (3.5 oz.)
Sienna is ochre with a high iron oxide content. Unlike yellow ochres, which generally are opaque, siennas are more translucent. When a limonite, like sienna, is calcined (roasted) at high temperatures, its water content (hydration) is eliminated and it becomes a hematite (anhydrous), like burnt sienna. Our French sienna is from the last remaining European company operating the ochre deposits in the French quarries of Gargas and Rustrel nestled in a 12 mile long enclave in the heart of the Luberon Mastiff, the ochre country.
raw Sienna, Sienne naturelle, siena-erde, Terre de Sienne, Terra di Siena
Origin and History
The pigment sienna owes its name to the Italian city, Siena, located in the Tuscany region. An area of rolling hills, it is famous for the mining and production of the pigment from the Renaissance until World War II. During the last two decades, as the Tuscan deposits became depleted, Italian siennas have come from other places in the country, such as Sicily and Sardinia. Sienna also have been mined in Germany's Hartz Mountains, but these are of lesser quality. Sienna has been used as a pigment since prehistoric times, although its name and variety came into usage since the Renaissance.
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.
: 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.
Sienna is hydrated iron oxide closely resembling yellow ochre (See
) by its composition. The content of hydrated iron oxide in sienna varies from 40 to 70% while in ochre it may be less than 20%. A. H. Church reports the typical constituents of sienna based upon three analyses given by M. G. Hurst: Hygroscopic water 8.2 to 17.5%; combined water which includes traces of organic matter 9.0 to 12.4%; manganese dioxide 0.6 to 1.5%; iron oxide 45.8 to 59.7%; and silica 5.0 to 17.4% [The Chemistry of Paints and Painting, p. 230]. The differences in color between ochre and sienna, is most likely due to the degree of hydration, or quantity of water bonded to its ferric oxide content. These pigments are basically composed of the minerals
associated with varying proportions of mineral impurities such as clay, chalk and silica.
Permanence and Compatibility
Sienna does not react with other pigments and is effectively used in fresco, oil, tempera and watercolors. It is considered to be permanent with medium tinting strength and excellent transparency. It does not react with solvents, and is indifferent to alkalis, but is partially soluble in acids.
Oil Absorption and Grinding
Sienna requires the largest proportion of oil of any other pigment to make it into a satisfactory oil-based paint. The finished paint will contain only 30% pigment. The oil absorption ratio is 12–18 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 12 to 18 grams (by weight) of pigment to form a stiff paste. It forms an average to fast drying oil paint, and a hard, fairly flexible film.
The pigment is considered to be non-toxic, but care should always be exercised when handling the dry powder pigment so as not to inhale the dust.
Pigment: Sienna (Luberon)
Pigment Brown 7 (77491) (77492) (77499)
Hydrated Iron Oxide (partial component)
ASTM Lightfastness Rating
na=2.260 nß=2.393 n?=2.398
Read cautions about handling pigments
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