Geode crystals can be made over a course of a few days inside an empty egg shell.
- Boil a saucepan of water and add salt to that water
- When the salt has dissolved, add food colouring
- Put the empty egg shell into the solution and leave over a course of 3 days
- Crystals will start to form on the inside of the shell
- If the required amount of crystals is not yet formed, leave in for longer.