Realgar
Composition and Properties of Realgar
Realgar is orange arsenic sulfide with the formula AsS, As2S2 or As4S4. It occurs naturally as a mineral and can also be prepared artificially. It darkens on heating by regains its original color on cooling and it less lightfast than orpiment and exposed to light it can be transformed into orpiment.
Names
Orange orpimentPY 39From late Middle English, from Arabic rahj-al-gãr, dust of the cave.
Preparation
The mineral has to be broken, ground and purified.Preparation of artificial realgarThe pigment can be prepared by heating and subsequent sublimation of mixture sulfur and arsenic oxide in the correct proportion so as to avoid the production of orpiment.
History of Use
The pigment has been found in Roman artefacts and was used rarely in oil painting in later periods.Examples of use
Quote
The two oxides [cuprous oxide & cupric oxide of copper were used in glass-making; verdigris was manufactured and put to several uses; white lead was used as a cosmetic by the Athenian ladies, and found further use as a medicine; red lead was used as a paint; stibium, or native antimony sulphide, was used as a paint for the eyelashes, and is still used for that purpose in the East under the name of kohl; black oxide of manganese was used in glass-making, especially for clearing up darkened masses, and so got its name of pyrolusite; the native carbonate of zinc was also known and used; the sulphides of arsenic, orpiment and realgar, were well-known pigments.
Source: A Short History of Chemistry
