Orpiment
Encyclopedia
Orpiment, As2S3
, is a common monoclinic arsenic
sulfide
mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity
of 3.46. It melts at 300 °C to 325 °C. Optically it is biaxial (−) with refractive indices
of a=2.4, b=2.81, g=3.02.
Orpiment is an orange to yellow mineral that is found worldwide, 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 is often found in association with realgar. It takes its name from the Latin auripigmentum (aurum − gold + pigmentum − pigment
) because of its deep yellow color.
and was used as a medicine in China
although it is highly toxic. It was also used as a fly poison and to poison arrows. Because of its striking color, it was also a favourite with alchemists
searching for a way to make gold, both in China and the West.
Orpiment was ground, processed and used for centuries as a pigment
in painting and for sealing wax, 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 material ended almost entirely with the advent of the cadmium yellow
s and the various dye
-based colors of the 19th century.
-transmitting glass, oil cloth, linoleum; in semiconductor
s and photoconductors, as a pigment and in fireworks. Mixed with two parts of slaked lime, orpiment is still very commonly used in rural India as a depilatory
. It is also used in the tanning
industry to remove hair from hides.
Arsenic trisulfide
Arsenic trisulfide is the inorganic compound with the formula As2S3. This bright yellow solid is a well known mineral orpiment , has been used as a pigment, and has played a role in the analysis of arsenic compounds. This chalcogenide material is a group V/VI, intrinsic p-type semiconductor and...
, is a common monoclinic arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
of 3.46. It melts at 300 °C to 325 °C. Optically it is biaxial (−) with refractive indices
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
of a=2.4, b=2.81, g=3.02.
Hot Springs
Hot Springs may refer to:* Hot Springs, Arkansas** Hot Springs National Park, Arkansas*Hot Springs, California**Hot Springs, Lassen County, California**Hot Springs, Modoc County, California**Hot Springs, Placer County, California...
and as a byproduct of the decay of another arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
mineral, realgar
Realgar
Realgar, α-As4S4, is an arsenic sulfide mineral, also known as "ruby sulphur" or "ruby of arsenic". It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment . It is orange-red in colour, melts...
. It is often found in association with realgar. It takes its name from the Latin auripigmentum (aurum − gold + pigmentum − pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
) because of its deep yellow color.
Historical uses
Orpiment was an important item of trade in the Roman EmpireRoman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....
and was used as a medicine in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
although it is highly toxic. It was also used as a fly poison and to poison arrows. Because of its striking color, it was also a favourite with alchemists
Alchemy
Alchemy is an influential philosophical tradition whose early practitioners’ claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base...
searching for a way to make gold, both in China and the West.
Orpiment was ground, processed and used for centuries as a pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
in painting and for sealing wax, 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
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
-based substances such as verdigris
Verdigris
Verdigris is the common name for a green pigment obtained through the application of acetic acid to copper plates or the natural patina formed when copper, brass or bronze is weathered and exposed to air or seawater over a period of time. It is usually a basic copper carbonate, but near the sea...
and azurite
Azurite
Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It is also known as Chessylite after the type locality at Chessy-les-Mines near Lyon, France...
. The use of orpiment as a pigment material ended almost entirely with the advent of the cadmium yellow
Cadmium pigments
Cadmium pigments are a class of pigments that have cadmium as one of the chemical components. They are highly toxic and can produce cadmium poisoning. Most of cadmium produced worldwide is used in the production of nickel-cadmium batteries, but about half the remaining consumption, which is about...
s and the various dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
-based colors of the 19th century.
Contemporary uses
It is presently used in the production of infraredInfrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
-transmitting glass, oil cloth, linoleum; in semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s and photoconductors, as a pigment and in fireworks. Mixed with two parts of slaked lime, orpiment is still very commonly used in rural India as a depilatory
Chemical depilatory
A chemical depilatory is a cosmetic preparation used to remove the hair from the skin on the human body. Currently, a common active ingredient is calcium thioglycolate, which breaks down the disulphide bonds in keratin and weakens the hair so that it is easily scraped off where it emerges from the...
. It is also used in the tanning
Tanning
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...
industry to remove hair from hides.
External links
- Webexhibits "Pigments Through the Ages: Orpiment"
- Babylonian Talmud Tractate Chullin see RashiRashiShlomo Yitzhaki , or in Latin Salomon Isaacides, and today generally known by the acronym Rashi , was a medieval French rabbi famed as the author of a comprehensive commentary on the Talmud, as well as a comprehensive commentary on the Tanakh...
'haZarnich'