Most hide glue is sold as a solid in granular or pearl form. To prepare hide glue for use, estimate how much solid glue you can use up in a few days to a week or more (it’s myth that you need to throw out the glue at the end of each day), and soak it in water for 20 minutes to a few hours depending on the particle size. The larger the particles the more time they will need to become fully saturated (mushy).
The glue comes in various gram strengths. The higher the gram strength the stronger the glue, but the faster it sets up. So there’s a trade-off. I’ve used 192 gram-strength glue for decades and find it plenty strong and easy to work with. Most musical-instrument makers and repairers use 251 gram strength, or even higher. But they are usually working on smaller objects.
For 192 gram-strength glue, use a ratio of about 2-2/3 cups of water to one pound of glue. (For your first batch I suggest you use 1/4 lb. of glue and 2/3 cup water so you don’t waste too much glue.) Higher gram strengths will require more water. You can always thin the glue later by adding more water or thicken it by adding more pre-soaked glue or by cooking off some of the water.
After adding the solid glue to water, stir for 10 or 20 seconds to prevent the glue from lumping at the bottom of the container. When all the glue has swollen with water, heat it to at least 130° Fahrenheit, but don’t let it boil. This should turn the glue into a liquid about the thickness of yellow glue. The glue will remain in a usable liquid condition as long as you keep it above 130° F (the ideal being 140° F to 150° F). When the glue cools to about 95° F, it gels, and you will have to reheat it to use it.
You can buy a special electric glue pot from many woodworking suppliers to heat the glue. Or you can simply put a small pot or jar containing the glue into a larger pot of hot water, which you can keep hot on a stove or electric hotplate. (Remember, our woodworking ancestors didn’t have electricity, and they got along fine.)
After a short time, a skin will form on the surface of the glue due to contact with the cooler air. The first time you heat the glue this skin may contain some dirt or other foreign matter. The skin will usually appear slightly lighter in color than the glue underneath. It’s good practice, but not absolutely necessary, to remove this skin using a stick or brush, and throw it away.
From then on, you can stir the skin back into the glue if more forms. Redissolving skin won’t weaken the glue. But the glue will become thicker due to water evaporation, and you’ll eventually need to add more water. It’s good practice to hold the moisture in and prevent the skin from forming by keeping the container covered when you’re not using the glue. A plastic coffee-can lid, with a cutout for protruding brushes, works well as a cover. You can keep the glue hot all day long if you want, or you can reheat it as you need it.
Hide glue often smells like rotten meat when it is heated. Many people find this odor offensive and thus don’t use the glue. The odor is caused by bacteria that wasn’t adequately removed at the factory where the glue was made. The sole remaining American hide-glue factory, Milligan & Higgins, takes extra care to clean the glue, and it thus has relatively little odor. Distributors for Milligan & Higgins include: Woodworker’s Supply, Merit Industries, Tools for Working Wood and many musical instrument suppliers.
So if the smell of the glue you are using bothers you, switch to hide glue from Milligan & Higgins. If you can buy in quantities of 50 pounds or more (possibly by dividing the glue with some friends), you can buy directly from the factory: milligan1868.com.
An alternative way of dealing with the bad smell is to mask the odor by adding one or two drops of wintergreen oil or citronella oil.