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