Thursday, February 25, 2021

Hoof Glue

A couple of weeks ago I wrote about hide glue, an adhesive made from animal hides that has been in use for thousands of years. Very simple to make and use, hide glue is not the only “animal glue” that humans have developed over the years.

Hoof glue is exactly what the name says: a glue made from the hooves of animals. For most of human history people have not had the luxury of “too much”, and we figured out uses for every part of any animal used for food. “Use every part of the pig except the squeal” was the philosophy before everything became disposable.

Whereas hide glue is made from the collagen in hides and bones, hoof glue is made from the keratin in hair and hooves. Animal hooves are nothing more than very thick versions of fingernails and are mostly keratin, the same protein that is a major component of hair. Animal horns (but not antlers) are also made of keratin. 

Both collagen and keratin are proteins (chains of amino acids) that have binding or adhesive qualities. When hydrolyzed (dissolved in water), they become “plastic” in the material sense -- soft, workable, and easily molded -- and when the water is removed they revert to their hardened state. Hoof glue retains more flexibility when dry than hide glue, making it a better choice for binding things that need to move or flex in use.

One of hoof glue's many uses was for sealing and bonding the sinew or fiber cordage used to hold arrowheads on the shafts of arrows. While not waterproof, the hoof glue was flexible enough to stay in place though the shocks of being launched from a bow and hitting a target. Binding layers of wood together to form a laminate which is stronger than solid wood was another use.

Like hide glue, hoof glue has a very long shelf-life. When stored in a dried form, there is a slight chance of fungal growth, but periodic heating and using it will keep it fresh and clean.

Making hoof glue is as simple as making hide glue but can be done on a smaller scale.

  1. Collect hooves or pieces of hooves (if you trim your livestock's hooves you have a good source).
  2. Break them into small enough pieces to fit into a small pot. Smaller pieces create more surface area and speed up the process.
  3. Add enough water to cover the pieces.
  4. Gently heat the mixture until dissolved, skimming off any debris that floats to the surface.
  5. An acid can be added at this time to form a gel if you have one available.*
  6. Add water or continue to heat (to remove water) until you get the desired consistency of glue.
  7. Apply while hot and allow to dry.

I remember first seeing hoof glue in a museum of natural history, it was in a display of some of the methods native Americans used to make arrows and bows. The hoof glue was a blob of dark material on a stick; it looked like a grotesque lollipop more than anything else, and it had a small clay jar with it. Since most of the tribes in the center of the US were nomadic, anything they carried from place to place was carefully thought out and size and weight were minimized. The “glue stick” was used by placing hot water in the clay jar and then stirring the water with the “glue stick” until enough had dissolved to make the consistency of glue needed. Any leftovers in the jar were warmed near a fire to drive off the excess water and then scraped back onto the stick for transport. Efficient, conservative of materials, and simple to use, this was a good way to have a multi-purpose adhesive on hand without taking up space or weighing too much.

* I'll see if I can put together a post about naturally occurring acids and bases for addition to the “chemistry for preppers” category.

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