During the long summer break it’s good to have a trick or two up your sleeve to entertain the kids on a rainy day. One of my…erm sorry their favourites is making slime! It’s fun and teaches them a bit of chemistry too.

What you need
White glue
Sodium tetraborate (Borax)
Sealable plastic bags
A large spoon
A jar with a lid
A bowl for mixing

Note: Borax is less easily available now than it used to be but you can buy it in good hardware stores, garden centres and online. Borax substitute doesn’t work! You’ve been warned.

How to make the slime
Place equal quantities of glue and water in the bowl, mix well with a spoon.

In the jar combine a cup of water with a tablespoon of sodium tetraborate powder or crystals. Screw the lid on tight and shake well. If all the sodium tetraborate dissolves add a bit more. You want a saturated solution. Keep adding a little more sodium tetraborate and shaking until no more will dissolve. Now your solution is saturated.

Add a small quantity of the sodium tetraborate solution to the glue and water mixture, and stir rapidly. The trick here is to add just the right amount of sodium tetraborate solution. Too little and there will be too much glue so the mixture will be sticky. Too much and it will be too liquidy. Add a small amount at a time and keep touching the mixture with your hand when it doesn’t look like liquid anymore. If it feels sticky, add a little more solution. If it feels too wet but not runny remove it from the bowl and knead it a little in your hands. It should gradually become more slimy as the excess sodium tetraborate evaporates. If it’s runny then you’ve probably ruined it! Try adding more glue but you may have to start again. I suggest you make a small amount to begin with to get a feel for proportions and texture.

When you’re happy with your slime you can colour it with food colouring and even add glitter, tiny plastic insects or tiny googly eyes. Slime keeps for a long time in sealable plastic bags. You can add a little more water if it starts to dry out.

The science bit!
The white glue and water mixture is a polymer. Polymers are used in all kinds of plastics and some cloth fibres like nylon. Sodium tetraborate is a cross-linking substance which binds the polymer chains together. This makes the glue solution thicker. If the polymer chains get too bound together it becomes more difficult for them to move around and the mixture becomes more like putty.

 By Louise Addison