Calligraphy: A Scribe's Notes Art Blog
Glair is a by product of egg use as an art material. Glair is added to gouache to make it adhere to the paper and not transfer off onto a facing page or other document. Some Gouache (rhymes with squash) pigments can be very soft when dry. Erasing around it can be a problem and the pigment can transfer off where you don't want it to. The addition of glair, "hardens" the pigment when dry and prevents it from migrating. It's simple and quick (10-15 mins) to make and you don't need very much.
Transfer the lot to a clean plate. Let the plate stand, tipping it up slightly on one side. You will soon see "tears" forming. Let the tears collect in a puddle on the low side of the plate. (3-5 minutes)
One or two drops of glair in a small well of gouache is sufficient. Too much will just make it thick. I have successfully stored glair in a dark bottle in the refrigerator for months. It may not last that long if it's picked up bacteria from the plate, dropper or your hands.
Check it every time before you use it. If it smells bad... it is. If you have any questions about making or using glair, leave me a comment.