Take me to the Steps

Note: This appeared in Make: volume 24. It was excerpted with permission from Sneaky Uses for Everyday Things by Cy Tymony (Andrews McMeel Publishing, 2003).

Don’t have a 3D printer to make plastic parts? Use moo juice instead. Ordinary cow’s milk contains a protein called casein. When separated from milk by using an acid such as vinegar, casein becomes a moldable plastic material that can be used to create everything from glue to fabric to billiard balls. Make your own custom parts for projects!

Cast your milk plastic in a mold
One way to shape your milk plastic is in a mold, like this silicone rubber one

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Project Steps

Cook the milk with vinegar.

Pour 1 cup of milk into the saucepan and warm it to a simmer, not a boil, on the stove.

Next, add 4 teaspoons of vinegar to the milk and stir. After a few minutes you should see white clumps form. When you do, keep stirring a few minutes longer, then turn off the heat to allow the pan to cool.

Strain the casein from the milk.

Pour the milk through a strainer into a bowl to separate all the white clumps (this is the casein plastic material), and place them on a sheet of wax paper.

Dry and mold the casein plastic.

Dry the casein plastic material by blotting it gently with paper towels until it’s dry.

Mold the plastic material into the shape(s) you prefer, and let it dry for at least 2 days. Once it hardens, you can color it with acrylic paint if desired.

TIP: If the casein is too runny to shape in your hands, next time add a pinch of cornstarch to the milk and vinegar mixture. This will make it hold together better.

Going Further

Shape your sneaky milk plastic into a sneaky finger ring that will attract paper U.S. currency! Just hide a small, super-strong (neodymium) magnet inside your ring before it dries and hardens. When the ring is placed close to a legitimate folded bill, the bill will move toward the ring because of the iron particles in the currency’s ink.

TIP: If the casein is too runny to shape in your hands, next time add a pinch of cornstarch to the milk and vinegar mixture. This will make it hold together better.