I have a very brief description of gelatine hardening on my page of hardener formulas. The URL is too long to post here, but you can go to the bottom of my Articles page and click on "Hardening Solutions for Film and Paper."(posted 8241 days ago)Essentially, gelatine hardening prevents the emulsion from swelling and increases its melting point. My information comes from "Fundamentals of Photographic Theory" by James and Higgins. I have read somewhere that a hardened gelatine layer doesn't necessarily have less water in it, just stronger bonds between the long strands of protein molecules, but I don't have a reference for that bit of information and can't guarantee its accuracy.