While researching hide glue I discovered that hide glue comes in various gram strengths. I've made 2 guitars so far with "Old Brown Glue" and have not had any problems with them so far. But on a "build your own lute" website (http://www.vanedwards.co.uk/glue.htm) the luthier recommended hide glue with a gram strength of 251 and other guitar luthiers on-line have recommended strengths ranging from 192 all the way up to 315. Do you think your Old Brown Glue rated at 192 grams is strong enough for classical guitar building? Is it possible for you to create a special batch of Old Brown Glue with a 251 gram strength rating? Thanks, Jeff

This is an interesting question. Gram strength of animal protein glues is a measure of the force in grams required to push a plunger into the surface of the glue a certain distance, measured by an instrument called a Bloom gelometer.
The higher the gram strength the harder the glue sets and the faster it sets. Lower gel strengths are more flexible and take longer to set. In woodworking the most popular gel strengths are 192 and 251. I have always used 192 (for 40 years) as I like the longer working time. As I am not a luthier, I do not know what qualities are important for your profession. I do know that reversibility is important. My experience with these glues tells me that the difference between 192 and 251 on good wood-to-wood joints is negligible. At this point, I have no desire to produce a version of OBG in another gram strength. Patrick