This is a great activity to introduce school age child to chemistry. As an added bonus they can then explore the results in a fun way in the bath.
Time: 15 minutes, plus at least 2 hours drying time.
Age: 5-10's, Over 10's
2 teaspoons sodium bicarbonate
1 teaspoon cornstarch
1 teaspoon citric acid
20 drops of glycerine
3 or 4 drops of vanilla fragrance
3 or 4 drops of colouring
1 mixing beaker
1 round mould (you can buy plastic moulds in craft shops)
1 mixing stick
1 packing stick
Find a clear workspace near a sink, and cover the area with newspaper or plastic.
Check your beaker is dry - this is a very important step.
Add the sodium bicarbonate, cornstarch, and citric acid to the beaker. Use a separate spoon for the citric acid.
Add 3 or 4 drops of fragrance.
Add 3 or 4 drops of colour.
Add 20 drops of glycerine.
Mix everything together evenly with your stirring stick. At this stage the mixture might fizz a bit. That's perfectly okay.
Once mixed, check the consistency. It should stay together in a clump when you pinch some together between your fingers, or you can scoop a little on a spoon. If it's not sticking, then add a little bit more starch and glycerine, then mix again.
IMPORTANT: Make sure your mould is dry. Pack the mixture into the mould using the bicarbonate spoon a little at a time. Between spoonfuls, pack firmly with the mixing stick.
Leave to dry overnight, and then gently ease apart.