Three natural adhesive families cover most jobs: hide and bone glue from animal collagen for woodwork and bookbinding, casein glue from milk curd for general use, and plant resins and tars for waterproof or hafting joints. A correctly made hide-glue joint can be stronger than the surrounding wood, but hide glue dissolves in water, so a joint that will get wet needs a resin or tar. Choose the glue by what the joint will meet, not by what is nearest.
Part of Organic Chemistry
Hide, bone, casein and resin adhesives, what each is made of, and which fits which joint.
Each Family Is A Different Polymer
- Hide and bone glue are collagen, rendered out of skin and bone by hot water, and set as they cool. The corpus pages are Adhesives, Hide Glue, Bone Glue, Fish Glue and Hide Preparation. The hide-glue page states that a correct joint fails in the wood before the glue.
- Casein glue is milk protein curdled with acid and set with lime. See Casein Glue, which gives the yield from a litre of skim milk, and Casein Extraction.
- Resin and tar are plant gums and wood-derived tars. See Pine Resin Adhesive and Resin Collection. Tar and pitch are different things: the chemistry pages distinguish them (Pitch Making for the tar-versus-pitch difference and Birch Tar for yields by method), and the materials pages carry the pyrolysis temperatures (Pitch Making (materials) and Birch Bark Tar). Neither pair is a substitute for the other.
- Shellac is an insect resin dissolved in alcohol: Shellac.
Which Glue For Which Joint
| Joint meets | Choose | Why |
|---|---|---|
| Dry interior wood, paper, leather | Hide or bone glue | Strong, reversible with heat and water |
| Dry joints needing longer working time | Casein glue | Sets by chemistry, not by cooling |
| Water, damp or outdoors | Resin, pitch or tar | Insoluble once set |
| A hafted blade or tool head | Pine resin or birch tar | Used for the purpose for a very long time (see the resin pages) |
The table’s water-resistance column is general craft knowledge and is not a corpus figure.
What You Need
- A glue pot with a water jacket (a pot inside a pot) so hide glue never boils or scorches.
- Raw material: hides and bones, milk, resin.
- Lime and vinegar for casein.
- A brush and clamps.
- A scale and a thermometer.
Method: Making And Using A Hide-Glue Joint
Step 1: Prepare and soak the hide pieces (see Hide Preparation).
Step 2: Simmer gently in the water bath; never boil, which weakens the glue.
Step 3: Strain and keep warm while using.
Step 4: Apply thin, join, clamp and leave to cool and dry.
Worked Example: Glue Solids
Hide glue is mixed by weight of dry glue to water. As an illustration, dissolve 100 g of dry glue in 200 g of water. Total mass is 100 + 200 = 300 g, so the solids are 100 ÷ 300 = 33%. Doubling the water to 400 g gives 100 ÷ 500 = 20% solids, a thinner glue that fills gaps less and sets slower. The ratio is a starting point, not a corpus figure; test on scrap.
Common Mistakes
- Using hide glue for a boat or a wet shed.
- Overheating hide glue. Boiling weakens it.
- Leaving casein glue standing. It has only hours of pot life per the casein-glue page.
- Thick glue lines. Thin joints are stronger.
Safety
Hot glue scalds, lime burns and resin solvents burn
Hot glue and hot resin stick to skin and cause deep burns; keep a bucket of cold water at hand. Slaked lime used in casein glue is caustic: wear gloves and eye protection. Alcohol used to dissolve shellac or resin is flammable: no flames, work in the open. Rotting hides and bone breed pathogens; wash hands and tools.
What’s Next
- Learn next: Plastic Alternatives — moulding and coating with the same natural polymers
- Combine with: Materials Synthesis — choosing among material families