Making Realgar Orange Pigment — The Arsenic Companion to Orpiment
Realgar (α-As₄S₄, also written As₂S₂ or AsS) is a vivid orange-red arsenic sulfide mineral that has been used as a pigment since antiquity. It is the chemical sibling of orpiment (As₂S₃) — where orpiment is golden-yellow, realgar is orange-red. Both minerals often occur together in volcanic deposits and hot spring environments. Ancient Egyptian, Chinese, and Roman artists used realgar for its brilliant orange colour, which no other ancient pigment could match.
Realgar has a unique instability: exposure to prolonged light causes it to convert to pararealgar (β-As₄S₄), a powdery yellow form. This photodegradation means realgar paintings that were once vivid orange may now appear faded and yellowish — a process that has been observed in medieval manuscripts and Chinese paintings.
SAFETY WARNING: Realgar is an ARSENIC COMPOUND and is HIGHLY TOXIC. Arsenic is a cumulative poison causing damage to the nervous system, liver, kidneys, and skin. ALL handling must be done with full respiratory protection (P100 respirator), chemical-resistant gloves, and eye protection. ALWAYS grind WET — never dry-grind realgar, as dry grinding produces respirable arsenic-containing dust. Work in a well-ventilated area. Realgar is INCOMPATIBLE with copper-based and lead-based pigments — direct contact causes chemical reactions that darken both pigments.
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