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Everything I've read says not to heat hide glue above 145°F because it will reduce its strength.

If you do get it too hot, is it noticeable, assuming you don't get it so hot that it starts to burn?

Kevin Looker

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I'm not a luthier.
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No. The 145 F is a compromise. You can heat (and certainly use) HHG way above 145 F. If you want a touch more open time you can heat it to say 190 F. It will be perfectly fine. You just can't heat it at 190 F for very long. The higher you go, the faster the collagen breaks down but it also breaks down at 145 F, it just takes much, much longer. The 145 F has become a bit of a mantra but in some ways it's a bit of a false one.

Hide glue can exist in several denatured states, but some of these transitions are a one way street. When the proteins are temporarily brought to a temperature where they uncoil (gel to liquid state), they will generally recoil and return to gel once allowed to cool. Once hide glue is warm enough to be liquid however, some of these strands will begin to break and shorten, the higher the temp, the faster this happens.

So there is no single magic temperature, just a balance between pot life and working time. 125°F will make it liquid, and perhaps leave the glue usable for many days of heat, but have no usable working time (unless you're working in a hot room). 185°F will give you plenty of working time, but keep a pot at this for an hour and the glue will be seriously compromised. The 145°F number is not anything absolute where a definable change will occur, just a reasonable average that most woodworkers find to be a good compromise.

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My small crock pot holds a water bath and the glue is in a Ball jar. Occasionally I forget it is on "high" and gets to 200deg. F.
I work in small batches, and regularly mix in a new bits of fresh glue, any "damaged" glue quickly gets diluted with new, stronger glue.
I go by look and smell, if I don't like the look (dark) or the smell ( rank) I toss it. Glue is pretty cheap.

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Thanks for the replies!

I was having no luck finding information beyond the basics when searching the internet.

Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.