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Milk is full of proteins called casein. When you extract these proteins, it forms a plastic.

Casein plastic dates back to the 1900s. It was used to make buttons, buckles, beads, fountain pens, combs, and other ornaments. It was even used in Queen Mary’s jewelry!

Today, it is still commonly found in food packaging, foams, paint, adhesives, glues, fabrics, and textiles. Here’s how you can make your own.

Directions

Milk to Plastic Experiment

Heat 1 cup of milk to almost boiling in a pan, then take it off the burner.

Milk to Plastic Experiment

Stir in 4 tsp of white vinegar and mix for one minute.

Milk to Plastic Experiment

Pour it all into a strainer.

Milk to Plastic Experiment

Scrape what’s left onto a paper towel. (It will have a gloppy consistency.)

Milk to Plastic Experiment

Pat out the liquid. The more you get out, the sturdier the plastic will be.

Knead in food dye or glitter.

Milk to Plastic Experiment

Mold it or press it into cookie cutters. We made fridge magnets and decorated the tops with paper måché, but here are a few other options:

Milk to Plastic Experiment
  • Keychains
  • Christmas ornaments
  • Candle holders
  • Pots and saucers
  • Hand-print tiles

How Does It Work?

When you add vinegar to your milk, it changes the acidity levels. The heat on the stove speeds up the reaction, and the casein proteins in the milk begin to separate and clump together—or coagulate—unfolding and reorganizing into a long chain called a polymer. Poly means many—and for good reason, because it’s a collection of all the single molecules (or monomers).

This long chain of molecules causes high molecular weight, which is why you can scoop the casein out and knead it like a dough.