Orpiment

Orpiment is a bright yellow arsenic sulfide mineral with the formula As₂S₃. Its vivid color made it a historical pigment, while its arsenic content made it toxic and useful as an arsenic source.

Arsenic trisulfide: Arsenic trisulfide is a chemical compound composed of arsenic and sulfur, with formula As₂S₃. Orpiment is the naturally occurring mineral form of this compound.
Layered material: A layered material consists of sheets of atoms or molecules bonded more strongly within sheets than between them. Orpiment’s sheets help explain its easy cleavage and softness.
Yellow pigment: A yellow pigment is a material that gives a substance a yellow color by selectively absorbing and reflecting light. Orpiment was prized for its intense yellow in paintings and manuscripts.
Arsenic poisoning: Arsenic poisoning is illness caused by exposure to toxic amounts of arsenic or its compounds. Handling orpiment dust can expose people to arsenic compounds.
Lead-tin yellow: Lead-tin yellow is a historical yellow pigment made from lead and tin oxides. It offered artists a stable mineral yellow without orpiment’s arsenic chemistry.
Crystal structure: A crystal structure is the ordered arrangement of atoms or ions in a crystalline solid. Orpiment’s layered atomic arrangement underlies its cleavage and optical behavior.
Optical absorption: Optical absorption occurs when matter takes up light energy at particular wavelengths. Selective absorption by orpiment leaves reflected light with a vivid yellow appearance.
Manuscript illumination: Manuscript illumination is the decoration of handwritten books with pigments, gold, and ornamental designs. Orpiment supplied vivid yellow passages in medieval and early modern manuscripts.
Art conservation: Art conservation is the study and practice of preserving artworks and cultural heritage materials. Conservators identify orpiment to manage its toxicity and prevent pigment damage.
Naples yellow: Naples yellow is a historical pigment based chiefly on lead antimonate. This opaque yellow competed with orpiment in European painting.

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Arsenic trioxideRelated: This natural arsenic ore has also served as a source of arsenic compounds.