Animal protein glue has been around for a long time. Its use predates known written records. By around 2000 B.C. written procedures on animal glue use emerge in Ancient Egypt. How is it possible that such primitive, ancient material can still be useful in a luthier’s workshop today?! It turns out that this glue has many beneficial properties, one of which is referred to as reversibility. When needed, glue joints can be released cleanly, without tearing-up the wood and destroying delicate surfaces of guitar soundboards.
Hide glue consists of rendered animal collagen, extracted from skins and tannery byproducts. It is similar to gelatin sold in grocery stores, albeit less refined. With proper technique, wood joinery with hide glue is strong, with nearly invisible glue lines.
To prepare a batch of hide glue for use, it is soaked in cold water, allowed to swell, and then gently heated to 140-150 F, at which point it turns into a honey-colored liquid. Lately, I’ve been using antique 19th century cast iron glue pots.
Traditional glues have been largely supplanted by modern synthetic adhesives, although not entirely. Guitarmakers, museum conservators, period furniture restorers and woodworkers, along with a few other specialty trades continue to rely on this time-tested adhesive.
For lutherie geeks (since you are still reading)! :)
Over the years, I’ve experimented with different glue heating contraptions; from larger commercial pots, to DIY, re-purposed contraptions. The one below was made from a yard sale special, a water heating pot. After all, we just need a warm water jacket around our glue vessel. Not the fanciest set-up, but it worked okay. The temperature control (rheostat) on this tea pot was not very sensitive, and maintaining stable temperature was tricky.
I also used the same pot with a baby food jar, installed in the original teapot lid (modified with an opening to accommodate the glass jar).
Here is a hefty, cast aluminum large capacity glue pot, with a solid copper liner. It was manufactured under Sta-Warm brand in the USA. I thought this pot was a higher-quality, sturdier version of a better-known Hold-Heet glue pot, which is still available through woodworking stores and luthiery supply houses. After using it a bit, I sold my Sta-Warm behemoth as it was too large for my needs. Otherwise, it was an excellent example of a plug-in type pot.
Currently, I use a laboratory hotplate to heat my glue pots. I like the absence of electrical cords around my bench. These antique glue pots are the original cordless equipment! Cast iron + water have enough mass and sufficient heat capacity to allow me to glue for 15-20 minutes before the pots need to return to the hotplate.
Slightly off-topic, but still related to hide glue….the glue brush. Traditionally, they are made without metal, in order to prevent the glue from becoming stained or discolored. A traditional glue brush can be purchased from a violin supply house, or even better, it can be made in house! All that’s needed is a few minutes and some bristles.
Glue…the difference between a guitar, and a pile of kindling.