Add one tsp of bicarbonate of soda to 100ml of PVA glue, stir until fully mixed. Add your food colouring to the mixture and stir well, it can be whatever colour you like! Stir in small amounts of ...

The insoluble reactant chosen depends upon the particular salt required. For example, copper does not react with dilute acids, so this metal cannot be used. On the other hand, sodium is too reactive ...