A variety of recipes have been described for obtaining this blue-green patina on copper, brass, or bronze. It was originally made by hanging copper plates over hot vinegar in a sealed pot until a green crust formed on the copper. Another method, used in the Middle Ages, was to attach copper strips to a wooden block with acetic acid, then bury the sealed block in dung. A few weeks later, the block was to be dug up, and the verdigris scraped off. In eighteenth-century Montpellier, France, it was manufactured in household cellars, "where copper plates were stacked in clay pots filled with distilled wine." The verdigris was scraped off weekly by the women of the household. Copper(II) acetate is prepared by treatment of copper(II) hydroxide with acetic acid.
Summarize in bullet points some methods used to produce verdigris.
- Hang copper plates over hot vinegar
- Bury copper strips with wooden blocks and acetic acid in dung and dig up weeks later
- Stack copper plates in clay pots of wine
- Combine copper(II) hydroxide and acetic acid