The Science of Slime Part I

Slime is great to play with. Its ooey, gooey, runny, squishy, stretchy fun. Slime is also incredibly easy to make. We are sharing our favourite creepy oozey slime recipe, and the science behind these sticky creations.

Stay safe and follow these simple guidelines:

  • Only a parent or supervising adult should prepare the Borax solution.
  • Adult supervision is required during the making of slimes.
  • Never eat slime.
  • Wash your hands after you have finished playing with them.
  • When you are finished do not wash the slimes down the sink, throw the slime into the bin or compost (do not compost any Slime that contains polystyrene beads or PVA)
  • Food colouring stains surfaces and clothing. Before you begin, think about the clothes you are wearing and the surfaces you are working on.

Guar Gum Slime Recipe

You will need:

  • Bowl
  • Measuring Cup
  • Teaspoon
  • Food Colouring
  • Borax solution
  • Guar Gum
  • Glycerine or Shampoo

Guar gum can be found in the baking section of the supermarket, it is used to thicken soups.

Borax crystals can sometimes be found at the supermarket, in the cleaning isle. I have also found it at Bunnings and the Warehouse. You will need to prepare the borax solution a few hours beforehand. Luckily this solution will last a long time and create a lot of slime!

To make the saturated borax solution:
Boil ½ litre of water and add 1/2 cup of borax powder. Stir until all the powder has dissolved. Keep adding tablespoons of borax powder until no more will dissolve. Let the solution cool and then transfer it to a sealable bottle. Don’t worry if you start to see borax crystals forming. Before you use it give the bottle a good shake to dislodge the crystals. Borax should not be ingested: Keep the bottle out of reach of children and label it well.


1. In the bowl, combine 2 teaspoons of glycerine and ½ teaspoon of guar gum. Stir until well mixed.

2. Add ½ cup of water and a few drops of food colouring. Stir this really well to make sure you get all the lumps out.

3. Add ½ teaspoon of borax solution. Stir and stir and stir for at least 30 seconds. You should start to see large sticky blobs forming in the mixture.

4. Keep adding ½ teaspoon of borax at a time until the slime is the desired consistency. Stir the slime well after each addition.

5. The slime is finished when the whole thing has formed one large blob that is not too sticky to touch.

Experiment with your slime. Try adding other ingredients such as cornflour, PVA glue, shaving foam, soap, glitter, leaves and mud.

MOTAT teachers holding up orange slime with young kid

The sticky on slime

Slime is any fluid that behaves in an unusual way. It is usually thick and flows super slowly. By this definition lots of household items could be considered slimes!

Slime belongs to a class of fluids called ‘non-Newtonian’ fluids. This just means they don’t behave like regular fluids. Particles in regular Newtonian fluids don’t change their thickness when you apply pressure to them. Imagine if you were stirring a glass of water and it started to get thicker, that would be super strange!

Some slimes become thinner and runnier when they are stirred, these are called stir-thinning slimes. Think about toothpaste, ketchup and hair gel, what do they have in common? These are all thick fluids that start to get runny when you squeeze them. It’s awesome that these fluids are slimes, it would be very difficult to use a runny toothpaste or liquid tomato sauce!

Here’s a video that explains the science of getting tomato sauce out of the bottle

Slimes that become thicker and clump together when stirred are called stir-thickening slimes. Stir-thickening slimes include custard, cornflour slime and guar gum slime. Most store-bought slimes are stir-thickening.

A good way to test whether a slime is stir-thickening or stir-thinning is to hold some in your hand and gently turn your hand over. If it slowly oozes out of your hand it is stir-thickening. If the slime stay put it is stir-thinning.

MOTAT teacher with blue slime

What’s up with borax?

When we added the borax to our guar gum mixture it changed it from a thick fluid to an even thicker, gooey stretchy one. PVA glue slime also uses borax in the same way. But what exactly does the borax do to make the slime so thick and gloopy?

When guar gum is added to water it becomes thick and flows slowly. That’s because the guar gum particles are very large and very long. When borax is added it starts to link those long particles to each other. As more borax is added, more linkages are made between the particles until a large mesh of particles forms. This mesh is big and bulky and flows slowly, causing the slime to become thicker. Gently tugging the mesh causes it to unravel but it does not break apart, the slime has become stretchy and gloopy.

Imagine 100 children running around a field at random. Suddenly each those 100 children have linked arms with the person next to them, they keep linking up until all the children are connected in a big long line. Think about the speed at which this bundle can now run around. That’s a simple way to think about the slow flowing nature of slime

Stay tuned for our next Slime post on amazing Oobleck!