Realgar (arsenic disulfide) was one of the most brilliant orange pigments available before the modern era — used from ancient Egypt through the Renaissance. Its extraordinary brightness came at the cost of extreme toxicity.

Realgar is historically significant rather than practically useful — the orange of ancient manuscripts and medieval illuminations, achieved at the cost of the illuminator's health. It represents the price of colour in pre-modern times.

Used in Chinese Han Dynasty paintings and Egyptian New Kingdom papyri. Medieval illuminators who worked extensively with realgar developed chronic arsenic poisoning. The search for a safe, stable orange drove pigment development for centuries — not solved until cadmium orange in the 19th century.