Adding salt to improve the shine of your egg wash may be a myth, but there's another practical reason to do it.
An egg wash consists of a beaten egg thinned with a little water or milk, and it’s used to develop shine and golden-brown color on the surface of breads, pastries, and pie crusts. Some recipes specify adding salt to the wash, claiming that it creates a better shine, but that didn’t prove true in our experiments. We did find, however, that in addition to flavoring the wash, salt helps denature the proteins in the egg, making it more fluid and therefore much easier to brush evenly and gently over delicate doughs. We’ll be adding a pinch of salt to our egg washes from now on.