Pigment Information: Realgar
Current Names: German: Rauschgelb, Schwefelarsenik; French: réalgar; Spanish: rejalgar; Italian: realgar Obsolete Names: Risagallo Color: Yellow Red Colour Index: Not listed ASTM Lightfastness: Not tested Density: 3.5 Hardness: 1.5-2.0 Chemical Formula: As4S4
Realgar is red arsenic sulfide, usually described as aurora-red to orange yellow, and is designated as strong orange-yellow in Munsell notation 9.1YR 7.1/11.6. Realgar gets its name from the Arabic words for "powder of the mine" (rahj al ghar).
Where Found: It is usually found in mineral deposits of calcite along with orpiment and sometimes with other sulfide minerals, such as cinnabar. Excellent specimens of realgar were discovered in cavities of dolomite in Binnentale, Switzerland, and in calcite voids in Mercur, Utah, U.S. We obtain realgar from deposits in the Hunan province of China where it is found in large druses (cavities in a mineral filled with protruding crystals) of beautifully formed crystals. It exhibits an intense orange red color with a scintillating quality of the coarse ground pigment.
History of Use: It is an historical pigment having been found as early as the fourteenth century B.C. as lumps of raw pigment in an Egyptian tomb.
Permanence and Compatibility: Early authorities usually described realgar as fading readily, or at least to some degree on exposure to light, and it appears to be less permanent than orpiment. It is said to be incompatible with lead- or copper-containing pigments. Several medieval painting guides do not recommend mixing sulfide pigments with lead white, minium (red lead oxide) or verdigris. It cannot be applied to wet plaster, and hence is not recommended in wet fresco painting techniques. Realgar is synthesized by heating orpiment to a temperature over 150°C or by sublimation of arsenic and sulfur. Although, the manmade mineral closely resembles the color and composition of realgar, it appears to be more susceptible to color change when exposed to light than natural realgar. It can lose its red hue and deteriorate to orange-yellow pararealgar when exposed to light.
Oil Absorption and Grinding: No data has been published on the oil absorption properties of realgar. It is difficult to grind because of its micaceous structure. For this reason, it is often quite coarse. It has been suggested to add ground glass to the pigment to facilitate grinding and dispersion in linseed oil.
Toxicity: The toxicity of arsenic sulfide pigments has been known for years. Extreme caution must be used when handling the dry pigment to avoid exposure to skin, ingesting it or inhaling the dust. Care must also be exercised while painting with it in any medium.
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