With the sheer number of adhesives peering at us from every hardware store’s shelves, it is hard to believe that most glues seen on antiques fall into only one category: animal. Hide glues were used extensively, and almost exclusively, until the mid-twentieth century, when aliphatic resin glues were developed. Even today, with a plethora of choices, hide glue is irreplaceable in the shop.
But why would anyone be willing to use glue made from an animal? What qualities make hide glue useful, when so many other products are out there?
Animal-based glues take advantage of a wonder of the natural world: collagen. This is the gelatinous substance which literally holds all of us together: a protein which is the foundation of skin, bones, tendons, cartilage, and hooves (for those of us who sport those.) The oldest example of hide glue is about 8,000 years old.
Collagens are easily processed out of the waste products from meat packing plants, using heat and water. When dried and pelletized, hide glue keeps indefinitely. Liquid, ready-to-use hide glues have a shelf life of about a year.
What are some of the working advantages of hide glue? Here are a few:
- tack: parts stay put with minimal clamping, and joints actually close up during drying;
- reversibility: hide glue softens with heat, which means that parts or overlays can be readjusted if need be. Also, a little warm water enables you to take a part right off, even decades (or centuries!) later. This also is a great aid in solvent-free clean-up.
- strength: as strong as many synthetics on oak and maple.* It’s strength easily exceeds the strength of most woods you might be gluing.
- consistency: because it is thinned with water and heat, it can be custom-mixed to the consistency you need for the job at hand.
- creep-free: unlike synthetics, parts don’t slide around, and the glue doesn’t wick into places you don’t want it.
- universal: effective on a number of materials, including paper, cloth, metal, felt, and wood. Traditionally used in adhering beize on writing slopes, and felt hammers on pianos; used by ancient jewellers to hold gold granules in place before permanently soldering or fusing.
When working with hide glue, we mix up only what we need in a small silicone bowl. We pour in some granules and cover them with water. About an hour later, we pop it in the microwave oven for about ten seconds, and it is ready! A brush is the best applicator, and it can simply be rinsed with warm water if it gets too gummy. When we are done, we simply let the leftover glue set in the silicone bowl: it peels right off, into the garbage, like the jelly it is. When working with larger quantities, we use nesting steel bowls as a double-boiler, on a mug warmer.
Hide glue is an effective, and authentic, tool in any restorer’s shop. If you get over the mental hump of using it the first time, we are confident you won’t look back.