Hide Glue

While digging through the cupboards and drawers at my new work location, I ran across a container of something I haven't seen in years: hide glue. Once upon a time, this type of glue was the preferred method of joining pieces of wood due to its strength and clear finish. Modern chemistry has given us more convenient alternatives, but hide glue is still an option for times when the stores are closed or too far away and you have something that needs to be mended. Several decades ago I learned how to make this basic glue on a scouting trip, and if a bunch of pre-teen boys can make it, I'd bet that a majority of you could, too.

Hide glue is, as the name implies, a glue or adhesive made from animal hides. It was one of the first adhesives that humans developed and has been in use for at least 6000 years. It dries clear, is strong enough for furniture joints, and is cheap to make. The downsides are that is is not waterproof and it does have a noticeable odor when wetted for use. 

The ingredients are simply animal hide and water. The tools needed aren't any more complicated: a source of heat, a container that can handle that heat, a stirring stick, a piece of cheesecloth (or old T-shirt) and a knife. We used coals from a campfire and an empty stew can along with a suitable stick off of the ground and our ever-present pocket knives. The T-shirt didn't work as well as cheesecloth, but it did work.

Preparation

1. Clean the animal hide as best you can. Remove all hair, fat and tissue that you can; you want just the skin. Tanned leather will also work, so recycling an old pair of boots or shoes that are made of leather is another potential source. Found some roadkill that isn't fit to eat? Skin it and use the hide.
2. Cut the hide or leather into small pieces. Somewhere between the size of a dime and a quarter is small enough. Smaller pieces give more surface area and speed up the process, but if you get them too small they are harder to remove after processing.
3. Toss the pieces of hide or leather into the container and cover with water. Let it soak overnight to absorb as much water as possible.

Processing

1. Add more water if needed to keep the pieces covered.
2. Place the container on your source of heat and bring it to a simmer. You don't want to boil the leather, just get the water hot enough to leech the collagen out of the leather. This will be a rather smelly operation, so working outside is a good choice.
3. Heat the mixture until the pieces start to turn translucent. That's the sign that you've got most of the collagen out.
4. Remove from the heat and pick out the chunks of once-leather and discard them.

Finishing

1. Filter the hot liquid into a second container to remove as many impurities as you can. Cheesecloth will get the big chunks while still letting the thick, viscous liquid flow through.
2. Place the second container on the source of heat and simmer until most of the water is gone.
3. Test the resulting liquid by touching some to a fingertip and seeing if it is tacky or sticky. Once you have a sticky gel, you've made glue that is ready to use.
4. To store your glue, evaporate off as much water as possible by pouring it into a shallow pan or container and letting it dry. We used a solar food dryer to speed things up a bit, something that another group had been building while we played with the glue.
5. Once the glue has dried and is brittle, chop or break it up into fine pieces and place in an air-tight container in the normal cool, dry place that we all know is best for storing most everything. The shelf-life is indefinite once it has thoroughly dried.

To Use As Glue

1. Pour some of your glue crumbles or powder into a small container and add a bit of water. Add more water for thin, runny glue that will seep into porous surfaces, or add less for a thicker glue that will fill in gaps or holes.
2. If you need to speed up the dissolving process, stir and apply gentle heat until it is liquid again.
3. Apply like any other glue that you've used. Brushes work well with paper and flat surfaces, and pouring into holes works well for woodworking.

I'll cover a few other types of home-made glues in the next few weeks, since glue has been around for a long time and is used more commonly than most people think.