Orpiment (arsenic trisulfide, As₂S₃) and realgar (arsenic disulfide, As₄S₄) are arsenic sulfide minerals often found together in volcanic deposits. Known since antiquity and described by Theophilus and Cennini, who warned of orpiment’s toxicity. Orpiment yields a brilliant golden yellow; realgar produces vivid orange-red. Both prepared by grinding natural minerals and washing.
Incompatible with lead- and copper-based pigments, forming dark sulfides. Realgar is photosensitive and can transform to yellow orpiment or white arsenolite upon light exposure. Orpiment is more stable but still degrades over time. Both were valued for brilliance but their toxicity and instability led to abandonment by the 19th century.
Usage Timeline:
| Pigment | Prehistory <3000 BCE | Antiquity 3000 BCE–500 CE | Medieval 500–1400 CE | Early Modern 1400–1800 CE | Industrial 1800–1950 CE | Present 1950–today |
|---|---|---|---|---|---|---|
| Realgar/Orpiment |
Key Properties:
| Properties: | Orpiment: brilliant golden yellow; Realgar: vivid orange-red; Semi-transparent to opaque; High tinting strength; Photosensitive (especially realgar) |
| Usage: | Antiquity to 19th century |
| Source: | Natural/Mineral |
| Toxicity: | Acute toxicity (arsenic) |
| Fresco: | Limited (a secco) |
| Tempera: | Yes |
| Oil: | Yes |
| Chemical description: | Orpiment: As₂S₃; Realgar: As₄S₄ |
| Visualization: | Visible microscopy, X-ray (moderate opacity) |
| Identification: | XRF (As, S), Raman, SEM-EDS |