As a historian of the Renaissance and therefore the Middle Ages I found the following taken from the Notes & Queries section of the Guardian Weekly fascinating.
What role does the wax in your earhole fill?
In medieval times ear wax was discovered to be an important auxiliary addition to the main binding media in books. Beaten egg white at first becomes frothy and distils to a clear liquid upon standing. This is called glair.
When glair is disturbed by the process of grinding in colours with it, it once again becomes frothy but also develops tiny air bubbles, which, after being painted on, burst and make small holes in the final film. Some clever experimenter discovered how the addition of ear wax prevents the formation of these tiny bubbles, resulting in a smooth film.
This technique became well known among illuminators throughout Europe and was particularly important in the preparation of gold grounds and in tempering vermillion.
Christopher Smith, NSW, Australia.