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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

Steps

Step #1: Cook the milk with vinegar.

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Sneaky Milk Plastic
  • 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.

Step #2: Strain the casein from the milk.

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Sneaky Milk Plastic

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.

Step #3: Dry and mold the casein plastic.

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Sneaky Milk 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.

Step #4: Going Further

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Sneaky Milk Plastic
  • 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.

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