Verdigris is a green pigment produced through the application of acetic acid to copper. By extension, it also refers to the patina formed on copper when the metal is exposed to air or saltwater for a long period of time. It was therefore a common sign of a copper weapon past its prime.
At the height of the Italian Renaissance artists relied on verdigris as a green pigment for their paintings. Manufacturing of this pigment principally involved exposing copper plates to hot acetum and then grinding the resulting verdigris. Aside from its use in art, verdigris was also mixed with chalk and sandarach by the Assassins to create blinding powder.