§ Fine azure is ground in water, and then placed in a silver vessel, for it is of such a nature that it desires silver. If you have no silver dish, seek out a tin one, and place it in that. Then when the water has all evaporated or been poured off, add egg white, so the mixture can be used for illuminating. You should take care not to leave the egg white in the azure for too long, for it may foul. When you wish to vary it, you may add Apulian white. Or, if you add indigo to the azure, purple will be formed, a dark colour. And if you mix azure, brazil and Apulian white in equal proportions, it makes a tawny colour.