April 11th
There is a long history of using egg white in painting. It is one of the options suggested in De Mayerne as a medium for colours 'a destrempe'.
How to paint with egg white?
Cennino Cennini Thompson
P. 79 How to lay bole - using egg white whipped.
p.7 Shading on sheep parchment and shading. 'And you may likewise work and shade with colors and with clothlets such as the illuminators use; the colors tempered with gum, or with clear white of egg well beaten and liquefied.'
Cennino Cennini recommends whipping the egg white and standing it overnight.
http://medieval-whimsies.blogspot.com/2011/12/making-storing-glair.html

Thompson 'The Materials and Techniques of Medieval Painting'
'Media for illumination - Glair
...The basic, standard medium for illumination was glair. Glair is the name given to the white of egg which has been deprived of its natural stringiness by any of several methods. White of egg in its original state does not mix readily with water, but tends to preserve its structure. If it is whipped to a froth and allowed to stand, it turns into a watery liquid which flows smoothly from a brush or pen, and can be mixed in any proportion with water. It was sometimes prepared in the Middle Ages by squeezing the white of egg in and out of a sponge, instead of whipping it; and sometimes by the use of a wool or cloth filter. An anonymous eleventh-century tract in Berne, called De clarea weighs the relative merits of the different preparations:' there are two kinds of glair, one which is made by beating and the other by pressing. The one made by pressing is considerably more brittle or weak than the beaten kind, and is, moreover, contaminated; since, being repeatedly squeezed or filtered through wool or cloth, it picks up dirt from the hand of the person who presses it...'