Choosing and mixing hot hide glue
Patrick Edwards discusses the different types of protein glues, why you should be using them, and how to mix hide glue
The traditional glue pot disappeared from wood shops and trade schools soon after World War I when synthetic adhesives took over, leaving later generations of woodworkers to learn this secret of the craft on their own. Animal-protein glues have many advantages over synthetics. They are very quick-setting; transparent to stains, oils, and other finishes; easy to clean up; and reversible, making repairs possible. They are also organic in nature, and are not toxic to humans or pets. If you doubt the strength of animal glue even with the host of antique furniture that has survived for hundreds of years, check out the test in FWW #192 (“How strong is your glue?”), where hide glue stood shoulder to shoulder with yellow glues and epoxies.
All wood glues create a mechanical bond by penetrating the porous surface and solidifying there. But animal glues also create a strong molecular bond with wood, due to the attraction between certain molecules and atoms. The glue sets initially by losing heat, and then cures fully by losing moisture. As mentioned earlier, this process is always reversible, and can be repeated even after a century or more.
The right animal glue for you
Although there are many excellent organic glues—from fish, milk protein, rabbit skin, horse bone and hide, and vegetable compounds—I’ll focus on hide glue, the most versatile type for furniture making. Today, hide glues are sold either in pearl or granulated form; I recommend only the latter, which turns to gel very quickly when cold water is added.
Hide glue can vary in quality, and it can go bad if exposed to moisture. Some people have sworn off hide glue after buying poorly made or poorly stored animal glue from indiscriminate sources all around the world, and then experiencing joint failures. Others complain about the smell. Good-quality glue has a very mild animal odor. If it smells rancid, it is bad and should be thrown out.
I recommend Milligan & Higgins 192-gram hide glue for all furniture-making tasks; I’ve been using it for 40 years. It actually is a mix of bone and hide glues, and has an open time of 1 or 2 minutes at normal room temperature and humidity levels, setting up as it cools. You can order hobbyist quantities of Milligan & Higgins 192 from Tools for Working Wood or from OldBrownGlue.com.