Butter of Antimony was made by distilling powdered stibnite ore, or metallic antimony, together with corrosive sublimate, mercuric chloride, heating the mixture in a retort until a heavy, fuming, pale liquid or soft waxy solid distilled over, its texture and appearance giving it its descriptive name despite bearing no relation whatsoever to actual dairy butter beyond the visual resemblance. The preparation was one of the more heavily documented and widely repeated antimony compounds in the seventeenth century antimony literature associated with Basil Valentine and his followers, part of the broader intense period of interest in antimony's chemistry and its medicinal, and often dangerously purgative, applications.
Butter of antimony was itself used medicinally, applied externally as a powerful caustic to treat certain skin conditions and, far more riskily, taken internally in carefully measured, small doses as a purgative, a use that walked a genuinely narrow line between therapeutic and outright poisonous given antimony trichloride's real toxicity and corrosiveness. Its most important further use, however, was as the immediate starting material for powder of algaroth, made by pouring butter of antimony into water, a transformation covered as its own entry in this atlas.