ONE: Holding an egg over a clean bowl, carefully crack it so that the clear fluid starts to drain out.
TWO: Slowly and carefully transfer the yolk back and and forth between the two halves of the egg shell so that as much of the egg white drains as possible.2
THREE: Beat the egg white as if you are making meringue, it will start to form a stiff white "froth" on the surface. When egg whites are beaten, some of the hydrogen bonds in the protein break, causing the protein's structure to unfold. This change in structure leads to the stiff consistency.3
FOUR: Keep whisking.
FIVE: Whisk some more.
SIX: Cover the bowl and allow the egg white to sit and settle allowing the foam to become quite stiff. Leaving it covered overnight seems to be the recommended amount of time.
SEVEN: Spoon the white crust out of the bowl and dispose of it, usable glair is the liquid remaining under this frothy crust. Pour this remaining liquid into a clean screw-top jar, preferably air-tight. I found that pouring mine through a tea sieve helped to remove the last of the crust.
EIGHT: Date your jar(s) and store them at room temperature. I have been told that glair improves with age and that paint mixed with fresh glair will feel completely different from paint mix with aged glair.4
Dec 2011 (Update): The glair seems to have developed a slightly sulfurous smell as it has aged. I have now used it a couple of times as a paint binder which seemed to work quite well. I did experience a little cracking on one piece, but that seems to have been an isolated incidence.
1 - Class given by Guild Mirandola at Pennsic 39 (2010) experimenting with various forms of flat-size for use with gold leaf.
2 - The egg yolk can also be used as a pigment binder and forms the basis of "tempera" paint. Due to its soft nature, tempera is not recommended for use in manuscript illumination.
3 - http://en.wikipedia.org/wiki/Meringue - Type of Meringue
4 - "Old/aged glair is preferred to fresh glair. It is much less brittle when dry and a pure joy to paint with. Fresh glair can feel a little sluggish and resistant to go where you want it. Aged glair makes your paint flow like oxgall has been added." Maitresse Yvianne de Castel d’Avignon, OL, AEthelmearc - http://www.angelfire.com/pa/allthat2/scriptorium/paint.html
- Thompson, Daniel V. The Craftsman's Handbook "Il Libro dell Arte", Cennino d'Andrea Cennini. New York: Dover Publications, Inc., 1954.
- Thompson, Daniel V. The Materials & Techniques of Medieval Painting. New York: Dover Publications, Inc., 1956.