Personaly, between chrome alum , Glyoxal and Formalin, I have never observed an advantage in chrome alum over the other two hardeners. Glass plates are the only kinde of emulsions I make. Glass cleaning is vastly more important than glass adhesion promoters. While it is true that my emulsions contain silane, If I don't clean my glass to the standard of a "standing sheet" of water, I WILL see frilling and cratering. Please see my glass cleaning proceedure on and www. Also, one must be very careful of the type and amount of surfactant one uses when the substrate is glass. The wrong kind, or too much surfactant can realy destroy adhesion to glass. I like Triton X200, in tiny amounts.