S atoms and 1 As atom, and an exocyclic sulfido center attached to the As atom. also dissolves in strongly alkaline solutions to give a mixture of and . "Roasting" in air gives volatile, toxic derivatives, this conversion being one of the hazards associated with the refining of heavy metal ores: Contemporary uses As an inorganic photoresist Due to its high refractive index of 2.45 and its large Knoop hardness compared to organic photoresists, has been investigated for the fabrication of photonic crystals with a full-photonic band-gap. Advances in laser patterning techniques such as three-dimensional direct laser writing (3-D DLW) and chemical wet-etching chemistry, has allowed this material to be used as a photoresist to fabricate 3-D nanostructures. has been investigated for use as a high resolution photoresist material since the early 1970s, using aqueous etchants. Although these aqueous etchants allowed for low-aspect ratio 2-D structures to be fabricated, they do not allow for the etching of high aspect ratio structures with 3-D periodicity. Certain organic reagents, used in organic solvents, permit the high-etch selectivity required to produce high-aspect ratio structures with 3-D periodicity. Medical applications and have been investigated as treatments for acute promyelocytic leukemia (APL). For IR-transmitting glasses Arsenic trisulfide manufactured into amorphous form is used as a chalcogenide glass for infrared optics. It is transparent for light between wavelengths of 620 nm and 11 µm. The arsenic trisulfide glass is more resistant to oxidation than crystalline arsenic trisulfide, which minimizes toxicity concerns. It can be also used as an acousto-optic material. Arsenic trisulfide was used for the distinctive eight-sided conical nose over the infra-red seeker of the de Havilland Firestreak missile. Role in ancient artistry The ancient Egyptians reportedly used orpiment, natural or synthetic, as a pigment in artistry and cosmetics. Miscellaneous Arsenic trisulfide is also used as a tanning agent. It was formerly used with indigo dye for the production of pencil blue, which allowed dark blue hues to be added to fabric via pencil or brush. Precipitation of arsenic trisulfide is used as an analytical test for presence of dissimilatory arsenic-reducing bacteria (DARB). Safety is so insoluble that its toxicity is low. Aged samples can contain substantial amounts of arsenic oxides, which are soluble and therefore highly toxic. Natural occurrence Orpiment is found in volcanic environments, often together with other arsenic sulfides, mainly realgar. It is sometimes found in low-temperature hydrothermal veins, together with some