Orpiment is a golden orange or yellow arsenic sulfide mineral. Found in volcanic fumaroles, low-temperature hydrothermal veins, and hot springs, orpiment is widely used in art, medicine, and other applications until the 19th century.
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Orpiment is a lemon yellow to golden brown crystal often found in fibrous aggregates. It varies in shape and texture. It can be botryoidal, or resembling a cluster of grapes. It can be reniform, granular or powdery. Less often it forms as prismatic crystals.
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It has a Mohs hardness of 1.5 to 2 (softer than gold) and melts at 300 °C (570 °F) to 325 °C (620 °F). It's fairly easy to grind into powder pigment. The earliest oil paintings are thought to contain orpiment.
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Orpiment can be combined with indigo dye, creating rich dark green. In the Wilton Diptych (c 1395-9), the green pigment is used in egg tempera. Renaissance artists such as Raphael (Sistine Madonna 1513–14) use orpiment in painted clothing or background.
Orpiment takes its name from the Latin auripigmentum (aurum, "gold" + pigmentum, "pigment"), due to its deep-yellow color. Unstable and toxic, orpiment is nonetheless a favorite of pigment and dye makers and painters, with few bright yellows in the palette.
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Limonite (yellow ochre) and weld are two primary sources of yellow before the discovery of cadmium by accident in 1817. German scientist Friedrich Stromeyer is in the lab heating zinc when he notices one batch turn bright yellow.
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He considers it suitable for artists' pigments. The cadmium colors, from yellow through to red, are not sold commercially until the 1840s. Until then, orpiment is still the brightest yellow available.
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Used as a pigment, orpiment has a color described as lemon or canary yellow, and occasionally as golden or brownish yellow. It may be formed through sublimation, the intense heating of a solid which becomes a gas without going through a liquid phase.
In sublimation an impure form is heated, turns to gas, and the gas re-forms to tactile matter in a cooler zone nearby. In this case it's the orpiment. An arsenic sulfide mineral, it often presents itself in the area of sulfur mines.
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Orpiment is among the few bright yellow pigments available to artists until the 19th century. Extremely toxic, orpiment is incompatible with other, common, pigments such as lead. It dislikes copper-based materials including verdigris and azurite thus mixes poorly.
Medieval painting guides eschew mixing orpiment with lead white, red lead or verdigris. It has been mixed with indigo, red iron oxide, Prussian blue, green bice (artificial malachite) and smalt, blue glass colored with cobalt oxide and ground into pigment.
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Orpiment repulses wet plaster and can't be used in fresco painting, in which the paint must bind with the wall plaster. Hunters and warriors apply toxic orpiment to arrowheads. It's also used to kill insects.
Orpiment may form with realgar, another arsenic mineral. In Chinese, the names for orpiment and realgar are Ci-Huang (female yellow) and Xiong-Huang (male yellow). Orpiment is usually yellow hued and realgar is deep orange or red.
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As an arsenic product the mineral can cause arsenic poisoning especially through ingestion or inhalation. Arsenic poisoning is often difficult to identify because it can build up gradually.
Symptoms of arsenic poisoning include:
abdominal pain
nausea, vomiting
diarrhea
cough
chest pain
dyspnea (shortness of breath)
pharyngitis (sore throat)
arrhythmia (abnormal heart rhythm)
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Because of its striking color, orpiment piques the interest of alchemists in China and Europe, looking for a method of making gold. Alchemists are particularly fond of toxic pigments, elements and metals such as lead, mercury and sulfur.
In alchemy, mercury and sulfur, along with salt, are believed to be the tria prima, three elements from which all else is made. Orpiment also has been found in the decorations of Tutankhamun's tomb and ancient Egyptian scrolls, and on the walls of the Taj Mahal.
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In Egypt, lumps of orpiment pigment have been found in a tomb of the 14th century BCE. In China, orpiment is known for use in coloring lacquer. Orpiment is identified on Central Asian murals from the 6th to 13th centuries.
In a traditional Thai painting technique, still in use, yellow ink for writing and drawing on black paper is made with orpiment. Medieval European artists import orpiment from the near East.
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Orpiment is found on wooden altar fronts in Norway, polychrome (multi-colored pottery) sculptures and folk art. It's also popular in Bulgaria, Russia, and former Yugoslavia. In Venice, records show orpiment is purchased for a Romanian prince in 1600.
European use of orpiment isn't common in art until the 19th century. It's found in the palettes of some Impressionist artists. They're also among the first to use cadmium colors.
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In medicine, ancient Greek physician Hippocrates uses orpiment and realgar to treat ulcers, not fully aware of their carcinogenic and otherwise toxic natures. Arsenic and compounds have been used to treat diabetes, psoriasis, syphilis, skin wounds and joint pain.
Orpiment is used today for the production of fireworks and pigments. In rural India orpiment mixed with two parts of slaked lime is still used as a depilatory. It's also used in the tanning industry to remove hair from hides.
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Yellow orpiment degrades into water-soluble arsenic oxides. Because of their solubility, arsenic oxides spread into the immediate environment. In artworks using orpiment, migrating, degraded arsenic oxides are found throughout the multi-layered paint system.
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