I sent a request to a producer (Dr.Oetker) of gelatin about the strentgh of their product. This was the answer: Bloom (6,67% 10°C AOAC) 220-240g.
These numbers correspond ony partly with the definition of gel strength that you can find on Frets.com:
Glue is graded on a basis of its gel strength, a measure of how many grams of force it requires to depress a 1/2” plunger 4mm. into a 12.5% protein solution of the glue at 10° C.
How should I interpret the information from Dr. Oetker?
Dr. Oetker is a distributor of baking and other food products -- I think I'd avoid trying to get woodworking advice from that source. That said, their gelatin probably works fine as glue.
Woodworkers generally use hide glue in the range of 190-250 gram strength. Higher gram strength glues require enough more water to be used in the normal way that when the water evaporates in a well clamped joint, there's less glue adhesion and strength, so the very high strength glues can result in weaker joints.
I'd stick with (pun intended) the regular stuff from regular suppliers.
I don't think Dr. Oetker can tell a lot about woodworking either, but I think that their laboratory may know the specs of their products. It is the number 6,67 that puzzles me. If this is directly replaceaceble with the 12,5% in your article, this gelatine should be similar to a 12,5% solution at about 500 grams, which is far to high to be used for guitar repair.
6,67 in some places in Europe is how they write 6.67. The math would suggest the gram is roughly half the 220-240
some where on line I read about the hide glue and they use it to do the glass chipping on mirrors, the glue as it dries and shrinks it pulls the chip from the glass It seems like they used different glues will do different chips. I guess I will seach that again.
go to this site How to Glue Chip Glass instructions - Letterhead Sign Supply
A local small lumberyard gave me a couple pounds of hide glue out of a 30 gallon cardboard drum that had in the back. He said in the 70's he used to do that glass scalloping for local shops and showed me a couple of pieces left behind. Needless to say I have not used the glue for anything serious as it is 40 years old.
And the small packets of Knox gelatin are a great way to glue on a label without firing up the whole HHG rig
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