I know one of you kitchen whizzes will know this. When you bake a whole egg, such as in a muffin cup, what causes the hard, shiny surface? It's almost like cellophane and shiny? I know it must be related to why people use an egg wash to give a shine to a food, but I'm interested in the chemistry behind it, should anyone know. It's pretty, but a bit tough to then cut through to eat.