On making verdigris. If you wish to make verdigris, take a new pot, or any other hollow vessel, and put into the vessel some very strong vinegar, and arrange sheets of the purest copper over the vinegar, in such a way that they may not come into contact with the vinegar. And so cover it up, and seal it, and put it in a warm place, or underground, and set it aside for six months. And then you must open the vessel, and scrape off into a very clean dish the material which you find in it, and set it in the sun to dry.