Transcript: Grow your own crystals

Most of the Earth’s crystals may have formed by geological forces millions of years ago, but I’ve found a way of making crystals like this at home, in just a few days.

You will need the following ingredients: half a cup of hot tap water, two clean jars, kitchen paper, a nylon fishing line, an ice cream stick and three tablespoons of alum. Alum, or aluminium potassium sulphate, is used in pickling, but if your local supermarket doesn’t have it, a chemist should be able to order it in for you.

Pour the hot water into the [first] jar and add the alum a little at a time, stirring as you go. The idea here is for the alum to dissolve, so stop adding once the grains stop dissolving.

Now cover the jar with a sheet of kitchen paper, and leave it overnight to do its thing. (Here’s one I prepared yesterday, and if you look closely you will see the beginnings of the crystals.)

Pour the solution from the first jar into a clean jar. The ‘seed’ crystals will be left behind. Grab the biggest and best-formed – I think this one will do – and tie one end of the fishing line around it. Now tie the other end of the fishing line to your ice cream stick.

Hang the seed crystal into the jar, adjusting the line length so that the crystal is covered by the liquid but not touching the sides or the bottom of the jar. And then leave it for several days and watch it grow.

As the water evaporates, there is less room for alum to be dissolved. This causes it to crystallise out, and the favourite spot for this to happen is on the outside of your ever-growing alum crystal.

And, as time goes by, your crystals will grow and grow – maybe even into something really impressive!