The Proportions of Colours.
If one ounce of black mixed with one ounce of white gives a certain shade of darkness, what shade of darkness will be produced by 2 ounces of black to 1 ounce of white?
625.
Remix black, greenish yellow and at the end blue.
626.
Verdigris with aloes, or gall or turmeric makes a fine green and so it does with saffron or burnt orpiment; but I doubt whether in a short time they will not turn black. Ultramarine blue and glass yellow mixed together make a beautiful green for fresco, that is wall-painting. Lac and verdigris make a good shadow for blue in oil painting.
627.
Grind verdigris many times coloured with lemon juice and keep it away from yellow (?).
Of preparing the panel.
628.