When I started my first guitar in 1960 a friendly violin repairman in Berkeley CA showed me how to judge the right amount of water to use. He put a dab of glue between his thumb and index finger, and on separating them showed me the little fibers of glue that formed. He said that as long as the glue would form those fibers, it would work fine.
I have since heard that violin guys use hide glue thinned as much as 10:1 with water, and that they will use Knox gelatin for glue.
I've also heard that Knox gelatin has a gram strength of between 300 and 500. That would mean that it gels more rapidly than our regular 195 gram strength stuff, which could be helpful in gluing in the tentellones in my classical and flamenco guitars---tentellones, a corruption of dentellones, i.e. "teeth".
So, does anyone out there in lutherie-land know anything about these bits of received wisdom?
On frets.com Frank Ford has an article about doing repairs with Knox gelatin where small quantities of hide glue are needed. I used it tp repair a small crack and it worked OK, but the open time was really short. You might get in touch with him--he has way more experience with it than I (boy, is that an understatement!).
Frank, bless his heart, is sending me some 512 gram strength stuff to try out---short open time.
Short open time is an advantage when installing those little blocks we call tentellones. We just press them into place on the soundoard, and up against the side, and let the glue do the rest---no clamping.