There is no better way to engage young children in science that to offer to let them do ‘an experiment’. The golden rule before you begin anything vaguely scientific with a small child is to establish the very first law of laboratory safety. Don’t put anything in your mouth! Or, in any other orifice for that matter. So, not only must you not eat anything, you must not suck pens, or fingers, or hair, or anything else creative – and as soon as you have finished, you must wash your hands. With the boring bit – and the most important bit – dealt with, it’s time to get on.
You can buy crystal growing kits for an inflated price, (always a good birthday present for a boy or girl in case you are ever stuck for ideas) but you can equally knock something up from your kitchen cupboards.
You will need a plastic dish to grow the crystals in, a colourless pot from a ready meal or plastic beaker is good. The easiest source of crystals is good old sodium chloride – table salt, but there are others that are prettier. Try ammonium phosphate or ammonium nitrate (plant fertiliser) or buy a commercial salt from Amazon. I’ve got copper sulfate, which cost me a couple of pounds for a good size bag, although do check the safety data as some solutions can burn or stain. You then need hot water, not too much, about 50ml. You have to dissolve your salt in the water, and keep adding the salt until you have quite a concentrated solution, there should be a few seed crystals remaining. This is known as a saturated solution. You can add a few drops of food colouring, your crystals aren’t going to be pure and authentic, but they will look much prettier. Then put your dish in a warm place and wait. This takes a little patience but the water will evaporate and a beautiful crystal will be left behind.
Interestingly, crystals like to escape from their container and will exhibit a phenomenon called ‘crystal creep’ as they climb the sides of the dish. You can either make a cardboard ring to cover the edges of the dish so that the crystals fall back in as they crawl out, or just stand the dish in a saucer to limit the scope of the escapees.