Calomel/Horn Quicksilver/horn mercury – mercury(I) chloride, a very poisonous purgative formed by subliming a mixture of mercuric chloride and metallic mercury, triturated in a mortar and heated in an iron pot. The crust formed on the lid was ground to powder and boiled with water to remove the calomel.
Verdigris – Carbonate of Copper or (more recently) copper(II) acetate. The carbonate is formed by weathering copper. The acetate is formed by vinegar acting on copper. One version was used as a green pigment.
White lead – carbonate of lead, a toxic pigment, produced by corroding stacks of lead plates with dilute vinegar beneath a heap of moistened wood shavings. (replaced by blanc fixe & lithopone)
Venetian White – formed from equal parts of white lead and barium sulfate.
Zaffre – impure cobalt arsenate, formed after roasting cobalt ore.
Aqua fortis/spirit of nitre – nitric acid, formed by 2 parts saltpetre in 1 part (pure) oil of vitriol (sulfuric acid). (Historically, this process could not have been used, as 98% oil of vitriol was not available.)