Unflavored gelatin and animal gelatin are made from the same thing, using the same process, is sold in most grocery food stores, and can easily be used as musical instrument ‘Hide’ glue. Most hide glue used by Luthiers to make instruments have a set strength around 140 to 190 grams, while Knox brand gelatin from the grocery store has a strength of about 350 grams. Almost twice as strong!

The neat thing is that wood joints using hide glue can be easily taken apart with warm water and/or heat. Hide glue can also be used in well-made, tight joints because it requires only a thin coating, where other glue types such as Titebond require a thick coating. Hide glue is transparent and can be used as a pore filler by mixing with pigments or sawdust and it sands easily.

To make a strong hide type glue from Knox (Unflavored) Gelatin packets, you mix the dry gelatin with 3 times the amount of clear and clean cold water (about 3/4 oz. or 1/3 of a cup of cold water for each 1/4 oz. package of unflavored Knox gelatin). Because Knox Gelatin has higher strength than normal luthier hide glues, it needs a little more water than normal.

Stir the mixture until the water is fully absorbed, to about the mixture of ice slush, and then you can heat it up to no more than 150 degrees Fahrenheit to use it. The concoction should have a consistency like that of thick, clear paste. Don't let it boil, as boiling will reduce its strength, and don't mix it so that lots of air bubbles are introduced into it which will turn it milky white. It is important to keep the glue warm when you glue the parts together so that the glue stays in a liquid state before you apply the clamps. Joints must be clamped before glue begins to gel at around 95 to 100 degrees. When a hide glue joint is clamped, the glue should squeeze out all around the joint. If the glue which is squeezed out has the texture of cottage cheese, breaks up easily or turns to dust when rubbed with your finger, the joint may not have been clamped in time.

After the mixture is mixed properly, you have to heat it up to no more than 150 degrees in order to use it properly and for it to become liquid. Don’t heat the glue mixture too much, as stated before, and preferably use a glass, not a metal jar to contain the glue, and a long shaft stainless food thermometer to measure the temperature. I use a small ceramic or metallic stove pot filled with water, heated in the microwave or on the stove at medium-high, and set another small glass jar or heavy plastic shot cup with the glue mixture inside of the warm water to warm the paste to the right temperature. After it turns a clear liquid, you have a very strong 'hide' type of glue that dries almost crystal clear. It works just like the hide glue you buy from places like HERE or from violin maker suppliers like THIS ONE.

When the glue is ready, there should be a slight 'skin' trying to form on the glue. Any more 'skin' and the glue will become too thick to use. At this point a couple of teaspoons of water into the glue will fix this problem. If you rub it between your fingers, it should feel oily, but not thick. If it feels watery, it's mixed too thin. If this is the case, add just a bit more gelatin powder and mix very thoroughly.

Hide glue sets by gelling as it cools, and also functions as its own clamp. Once the hide glue begins to gel, it actually 'pulls' or 'sucks' the joint together. Hardening occurs only by evaporation, and this process is entirely reversible. Wetting and/or reheating or steaming the glue joint will bring hide type glues back to their original texture, a liquid. If the joint doesn't go together in time, you can wash off any of the already gelled glue with warm water and start over. When the glue forms a thick “skin” or reaches the consistency of mud or heavy paste, its too late to apply clamping pressure. Excessive thinning out of hide glue with more water than recommended will reduce the strength of the joint and cause bubbles which will turn it white. Any and all wood surfaces should be properly fitted and very tight fitting and clean before application of the glue.

HERE is a great FAQ on hide glue versus commercial grade wood glues. This particular website also touts that they have some of the best hide glue available. It's definitely cheaper than Knox Gelatin in large quantities by volume...