Casein plastic, or Galalith, makes good buttons, beads, knitting needles, pen bodies and small decorative items because it polishes to a high gloss, takes dye and machines like horn, but it must stay dry and cool. It softens and warps in water, fails above about 80 degrees Celsius, is too brittle for structural work and absorbs moisture, so it cannot serve as an electrical insulator.
Part of Plastics and Polymers
Casein plastic is a milk-protein material hardened with formaldehyde, used historically for small molded and turned goods.
What It Does Well
Casein plastic can be polished to a high gloss, dyed any colour and machined by drilling, turning and cutting. It replaces horn, bone and ivory for buttons, beads and decorative pieces. Plastics from Scratch lists the best uses: buttons, knitting needles, beads, small decorative items and pen bodies. The corpus’s Casein Plastic covers making it, and Casein Extraction the starting material.
Yield is modest. The carrier gives about 30 g of casein per litre of skim milk, which the extraction article puts at roughly 30 g per litre of cow’s milk.
What It Cannot Do
| Limit | Consequence |
|---|---|
| Absorbs water | Softens, swells and warps if immersed |
| Fails above about 80 °C | No hot-water use, no heat sources nearby |
| Too brittle for structure | Not for load-bearing or outdoor parts |
| Absorbs moisture | Poor, unreliable electrical insulation |
For anything electrical, use Bakelite: see Electrical Insulation. For anything that sees water or heat, use a different material, or see the thermoplastic and thermoset choice in Thermoplastic vs Thermoset.
Hardening Time Rises Steeply With Thickness
Hardening in formaldehyde solution works from the surface inward, so thick pieces take much longer, and the sources disagree on the strength of the bath. The carrier gives a 5-10% solution with 2-3 days for a 1 mm sheet, 2-3 weeks for a 5 mm block and 4-6 weeks for a 10 mm block. The corpus’s Formaldehyde Hardening gives a 4-5% bath with 3-5 days for a thin button and 2-3 months for a piece over 10 mm. These do not agree; the weaker bath gives off less formaldehyde vapour, so that is the safer one to start with, and this page changes neither figure. Dry slowly at room temperature, since fast drying causes warping and cracking.
Worked Example: Milk For A Batch Of Buttons
Suppose each button uses 4 g of dry casein (assumed) and you want 50 buttons: 50 × 4 = 200 g. At 30 g per litre, you need 200 / 30 = 6.7 litres of skim milk. At the 35 g per litre top of the range in Casein Glue, 200 / 35 = 5.7 litres. Plan for about 7 litres because trimming and cracking waste some.
Where Casein Fits Beside The Others
Compared with the others in the set, casein is the safest to make, because it needs only vinegar and a formaldehyde bath, and the least capable. Use it for objects, not equipment. It can be turned on a pole lathe (see Pole Lathe Build), which is how buttons and beads are made at small scale. For fittings see Buttons, Handles and Hardware.
Common Mistakes
- Using casein outdoors — water gets in and it swells and splits.
- Drying quickly in sun or heat — warping and cracks that cannot be repaired.
- Using it as insulation.
- Over-long immersion in formaldehyde — wasted solution and extra exposure.
Formaldehyde bath
Formaldehyde vapour irritates eyes, throat and lungs, and it is a carcinogen with long exposure. Keep the bath covered, work outdoors or well ventilated, wear eye protection and gloves, and keep it away from food and children.
What’s Next
- Learn next: Celluloid — the thermoplastic alternative
- Combine with: Machining Plastics — turning and drilling casein