Temper azure with egg white by rubbing it in a little dish until it is saturated. And then wash it free of the old, darkened egg, and after two or three days wash it again, on account of the egg which has grown old and dark. And set it aside until the moisture of the water has evaporated, and you will he able to illuminate with it again. Take some of the same colour, tempered in this way, or otherwise, in another dish. Put some of the gum which oozes out of the plum or cinus tree into clean water, and boil it until it becomes quite thick and sticky; take care not to let it boil over, but keep it and temper the azure with it. Whenever it seems dark to you, add a little milk.