Realgar

## Realgar Realgar

**Realgar** (arsenic disulfide, As₂S₂; Arabic *rahj al-ghār*, "powder of the mine") is an orange-red mineral closely related to orpiment, used in alchemy, medicine, and as a pigment. Like orpiment, realgar was classified as one of the volatile "spirits" that sublime completely when heated, and its bright color and sulfurous nature made it important in alchemical operations. Medieval Arabic and Latin texts describe realgar as a "hot" and "dry" substance, capable of "opening" metals and facilitating their transformation. Its red color associated it symbolically with the final stage of the Great Work (rubedo) and with the sulfurous, fiery principle.

Realgar was used as a red or orange pigment in painting and manuscript illumination, though less commonly than cinnabar due to its tendency to degrade when exposed to light, transforming into a yellow powder (arsenic trioxide or a mixture of arsenic compounds). In medicine, realgar was employed externally as a caustic and internally (in very small doses) as a treatment for various ailments, particularly in Chinese and Islamic medical traditions. Alchemical texts describe using realgar in combination with mercury, sulfur, and other substances in attempts to produce the red elixir or Philosopher's Stone.

The transformation of realgar to orpiment through gentle heating, and of both substances to white arsenic through more intense heating, demonstrated to alchemists the mutability of mineral substances and the power of fire to effect transformations. These color changes—red to yellow to white—could be read as a reversal of the alchemical sequence, or as evidence of the interconvertibility of the principles. Modern chemistry recognizes realgar as arsenic disulfide, which is indeed photosensitive and degrades to arsenic trioxide when exposed to light. The toxicity of realgar, like that of all arsenic compounds, made it dangerous to handle and use, though this was not fully appreciated in the pre-modern period. The substance's vivid color, its volatility, and its chemical transformations made it symbolically important in alchemy, representing the fiery, sulfurous aspect of matter and the red phase of perfection.

---