The Making of the Glencairn Methuselah Window: Page 17
dark brown color – with this I dissolved the white and yolk of egg, dropping it into them and stirring. I smashed the white with my finger somewhat and strained it.
7th I coated both sides of the drawing board with white of egg and Portulaca.
8th I mixed tempera color in tubes with plenty of yolk of egg and portulaca using a watercolor brush with long hairs