Long time since I wrote a "how to" post - This time, I thought to deal shortly with top coats and the traditional ways to finalize your work.
Egg-tempera is a very fine and durable material as long as it remains protected from insects (that really find it very... yummy) and moisture (and in case of Churches, the devastating effects of lipstick, that permanently stains, with its oils, the icon)
So, after completing painting, and letting a week go by (that is the time that egg-tempera really needs to dry)- We need to first protect and then totally isolate the colours.