Never temper green with vinegar. Put the best wine in a dish of bronze or copper, and boil it. When it has been boiled and skimmed, keep it and temper the green with it, and put it in warm or moderate sunlight until it becomes quite thick. And if you put saffron and the powder of calcified bones in it, it acquires a different, more handsome green color; or if you mix it with some of an old mixture that has been freshly prepared, it will be a still different shade of green. If it all dries up or becomes too thick, add a little water.