Varnish is the last step. It has two major functions: one is optic and the other, protective. The optic function is linked to refraction quality of varnish. Natural resins often have a refraction indication and transparent quality superior to synthetic varnish. Varnish reveals depth in a painting, as well as the successive coats of glacis applied by the painter. Without varnish, light stops at the first coat it comes in contact with.