Orpimenti

Orpimenti is the plural form used to refer to arsenic sulfide pigments, historically employed in art and decoration. The best-known member is orpimento, with the chemical composition As2S3, which produces a bright yellow color. A related pigment in the same family is realgar, As4S4, which yields an orange-red hue. Together, orpiment and realgar are often described as arsenic sulfide pigments.

Natural occurrence and composition: Orpiment and realgar occur as distinct minerals found in hydrothermal veins and sedimentary deposits. Orpiment typically forms vivid yellow crystals, while realgar appears orange to red. As sulfide minerals, they share chemical properties and can be sensitive to light and air, affecting their color over time.

Historical use: Orpiment and realgar have been used since antiquity in illuminated manuscripts, paintings, glass, and ceramics. Their striking yellow and orange tones made them valuable for highlights, gilding accents, and decorative details. Because of their toxicity and instability, their use declined with the development of safer synthetic pigments in modern times.

Stability and safety: Both pigments are light-sensitive and can darken or fade when exposed to light, humidity, or air, sometimes converting to arsenic oxides. They release toxic arsenic compounds if ingested, inhaled as dust, or heated. Consequently, handling and storage require caution, often involving proper ventilation, protective equipment, and avoidance in consumer products or cosmetics. In conservation practice, identification and careful management are essential to preserve artworks containing these pigments.

Modern context: Today, orpimenti are mainly of interest to art historians and conservators. When present, they are typically studied to understand historical palettes, painting techniques, and the provenance of artworks.