Making Hide Glue

The ingredients for making hide glue are quite simple: glue crystals, water, and salt if you want to extend the assembly time. You'll also need jars with a top, some type of scale to weigh the ingredients, a thermometer, and a way to heat the glue—a water bath using a cooking pot is easy. Nothing in this recipe is toxic and is in fact nutritious!

You can buy the dried glue crystals from online purveyors such as Woodcraft (www.woodcraft.com), Highland Hardware (www.highlandhardware.com), Woodworkers Supply (www.woodworker.com) or Kremer Pigment (www.kremerpigments.com). 192 and 251 gram strength glues are most common and wholly appropriate, 192 glue having a longer open time than 251. The crystals are soaked in a measured amount of cold, clean water for a few hours and subsequently heated until it is liquid. Some suppliers provide instructions and ratios but, in general, for 192 glue,  the ratio, by weight, of glue to water is 1:1. For 251 glue, the ratio of glue to water is 1:2 (twice as much water). 

To make hot hide glue, soak the glue granules in the appropriate amount of cold water  and set it aside for a few hours until the granules have absorbed all the water they can. The glue is then heated in a water bath at 140°F until all the glue is completely liquid. Some practitioners take the glue off the heat and refrigerate the glue and rewarm the mixture the next day. While not strictly necessary, you will avoid lumps in your glue by doing this. The glue is applied hot to one surface and the join is brought together and (this is important) before the glue has gelled. Depending on the situation, it may need to be clamped for a short while. You only have seconds to get the wood assembled so if you need more time, use liquid hide glue. To make liquid hide glue, simply add about half as much table salt as dry glue (by weight) to the mix. Heat as above and set aside. It will remain liquid. If a little too viscous, heat it in the water bath (140°F), just don’t cook it all day as the glue breaks down.

Since hide glue is a protein-based glue, once made it will grow mold and will undergo hydrolysis (protein breakdown by water). Most restorers make their own hot glue, fresh for the day it is going to be used. Cold glue can last much longer, maybe a month or two. Yes, it seems like a lot of work when you can buy a bottle of yellow glue in any hardware store. But the next time your precious antique needs work, you (and your restorer!) will be happy you didn’t make a mess of things with those other glues.

I use hide glue to glue joinery in objects that have been originally glued with hide glue. I use it for most veneer work for the ease of retreating the glue line should I have a failure. And I use it for work where I have good wood-to-wood mating surfaces and clamping is awkward, because hide glue, once gelled, is not going to give up its grip. For more about glue, go to this page,  Glues.

Hot glue presents issues with getting joins clamped fast enough as it gels very quickly—too quickly, usually. This is when you might wish to extend the gel time using table salt. If you add enough salt you will make cold, liquid glue similar to that which can be purchased. The only real advantage to making your own instead of prepared cold hide glue (Franklin's "Liquid Hide Glue" and "Old Brown Glue") is knowing the glue is fresh.  If you use cold glue, you will have plenty of time to assemble the joints and put clamps on as the glue no longer has a gel phase.  

Advantages to hot glue: once the join has been made and the glue gelled, the clamps can come off. It will not come undone very easily after a few minutes. You will have to limit your usage of hot glue to things which can be put together quickly, e.g. replacing a piece of wood that has fallen off, otherwise, use cold, liquid hide glue.