Glue

Glue is an adhesive substance used to bind materials together. Historically, the most common strong glues were made from animal collagen.

Description of what it is like

Animal glue is typically sold as hard, brittle, amber-colored granules, sheets, or blocks. When soaked in water and heated, it becomes a viscous, sticky liquid. As it cools and dries, it hardens and bonds surfaces together.

Origin and where to find it

• Environments: Anywhere animals are butchered or processed.
• Signs: It is a byproduct of processing animal parts (hides, hooves, bones).
• It is a processed material.

Minimum processing required

1. Collection: Gather scraps of hide, connective tissue, bones, or hooves.
2. Cleaning: Wash to remove dirt and blood. Soaking in lime water helps break down the tissue but must be rinsed off.
3. Boiling: Simmer the material in water for several hours to extract the collagen.
4. Straining: Filter out the solid residue.
5. Reduction: Simmer the liquid further to evaporate water and thicken it.
6. Drying: Pour into molds or trays to gel and dry into hard cakes for storage.

Tools needed to work on it

• Pot: For boiling.
• Heat source: Fire or stove.
• Strainer: Cloth or mesh.
• Glue Pot: A double boiler is essential for reheating the glue without burning it.

Common forms of use

• Hot Glue: Applied warm and liquid; sets as it cools (Hide Glue).
• Liquid Glue: Treated with additives (like urea or vinegar) to stay liquid at room temperature (Fish Glue).
• Gelatin: A purer form used for sizing paper or food.

Possible substitutes

• Resin/Pitch: For waterproof or gap-filling needs (but brittle).
• Starch Paste: Made from flour or rice, good for paper but weaker for wood.
• Casein Glue: Made from milk curds and lime, very strong and water-resistant.
• Modern Glues: PVA, Epoxy, Superglue.

Limitations and common failures

• Moisture: Animal glue is water-soluble and will fail in damp conditions or if it gets wet.
• Heat: It softens when heated (which makes it reversible, a benefit for instrument repair).
• Spoilage: Liquid glue can mold or rot if not preserved.

Risks and safety

• Burns: Handling hot glue pots.
• Smell: Boiling bones and hides can produce a strong, unpleasant odor.

Related materials

• Leather: Made from the same raw material (hides).
• Bone: A source of glue.
• Wood: The primary material bonded with glue.
• Water: The solvent for the glue.
• Resin: An alternative adhesive.
• Pine Resin Glue: A waterproof, natural adhesive.
• Duct Tape: A cloth tape that uses a rubber-based adhesive.