Orpiment is a common monoclinic crystalline mineral
– Chemical Composition: As2S3, arsenic trisulfide
– Molecular Weight: 246.04 gm
– Hardness: 1.5-2
– Optical refractive index: Biaxial (-), a=2.4, b=2.81, g=3.02
Orpiment is a mineral that is found world-wide, and occurs as a sublimation product in volcanic fumaroles, low temperature hydrothermal veins, hot springs and as a byproduct of the decay of another arsenic mineral, realgar. It takes its name from the Latin auripigmentum (aurum – gold + pigmentum – pigment) because of its deep yellow color.
Orpiment was ground, processed and used for centuries as a pigment in painting, being one of the few clear, bright yellow pigments available to artists up until the 19th century. Orpiment presented problems, however, such as its extreme toxicity and its incompatibility with other common pigments like lead and copper-based substances such as verdigris and azurite. The use of orpiment as a pigment matter ended almost entirely with the advent of the cadmium yellows and the various dye-based colors of the 19th century.
Orpiment is also known as “King’s yellow”