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.