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  • 8 June 2006 | Updated 2 November 2012

Borax slime

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Safety: This activity uses borax which is harmful when swallowed. For more information, visit the CSIRO Education safety page.

You will need

  • PVA glue    
  • Food colouring
  • Water
  • Borax (from supermarkets)
  • 2 plastic cups
  • Sealable plastic bag
  • Pop stick
  • 2 plastic spoons

What to do

  1. Measure 3 teaspoons of PVA glue into a plastic cup.
  2. Add 3 teaspoons of water and stir.
  3. Add a couple of drops of the food colouring of your choice.
  4. Place just less than 1 cup of water into the other plastic cup.
  5. Stir in 1 heaped teaspoon of borax powder. Once the mixture has been stirred thoroughly you have made a borax solution.
  6. Add 1 teaspoon of borax solution to your jar of paste and stir. As you stir the slime should start to form. You might need to add a little more borax solution. Be careful when you are adding the borax solution, too much and your slime will go hard.
  7. If your slime feels very wet and slippery (but is not still runny), remove it from the container and kneed it in your hands. In a few minutes, any extra borax solution will evaporate or be absorbed.
  8. Place the slime into a sealable plastic bag and it should keep for a while.

Note: If you get slime onto fabric or carpet it can be removed with a little vinegar followed by warm soapy water. Make sure you wash your hands before and after playing with the slime.

What's happening?

The borax is acting as the connector for the PVA glue (polyvinyl acetate) molecules. Once the glue molecules join together to form even larger molecules, called polymers, you get a thickened substance very similar to slime.

When you mix glue with a bit of water, you make a substance that is known as a polymer. Polymers are very large molecules, formed by repeated patterns of chemical units strung together. The borax solution is a 'cross-linking' substance that binds the polymer chains together to make the glue solution thicker.

As the polymer chains get more 'cross-linked', it gets harder for them to move around, and your slime starts look like putty. Experiment with adding more borax solution to see if this indeed makes the slime thicker.

The trick to this experiment is knowing how much borax to add. It you add too little, your slime will be too sticky due to the excess glue. If you add too much borax there will be too much 'cross-linking' and it won't feel like slime.

This activity was featured in Science by Email