In the early 1900’s until about 1945, plastic made from milk, known as casein plastic, was quite common. It was used to manufacture buttons, decorative buckles, beads and other jewelry, as well as fancy comb and brush sets.
All plastics are polymers. Sometimes polymers are chains of just one type of molecule; in other cases, polymers are chains of different types of molecules. Milk contains a protein called casein. When you heat milk with an acid, the casein molecules unfold and reorganise into a long chain. Each casein molecule is a monomer and the resulting polymer that forms casein plastic is made up of lots of casein molecules joined together. Equipment
1 cup (250 ml) of milk, any kind of animal milk will work
4 tablespoons of white vinegar
A mesh strainer
Anything you want to decorate the plastic
Pour the milk into the saucepan and heat it until it is just under boiling, stirring continuously.
Add the four tablespoons of vinegar to the milk and stir for about 1 minute. As you stir, you should notice that clumps will start to form. If this isn’t the case, the milk wasn’t hot enough for the reaction to occur.
Place the strainer on top of the bowl. After letting the milk cool a little bit, pour it over the strainer and let it drain.
Scoop the curds out of the strainer onto paper towels and squeeze the curds to get out any extra moisture.
If you want to make something out of your plastic, it needs to be done in the first hour while the curds are still moldable. Wait until the curds have cooled completely before handling them. Before you begin, squeeze all of your curds together into a dough like substance. Once it’s clumped together into one blob, knead well until it is easy to shape and form. Mold the dough into any form you want.
Leave the plastic to dry for a few days.
Once dry, you can decorate your plastic however you want.