Crystal Grower

Crystal structures are found in various places in nature – snowflakes and minerals, or on the edge of hot springs.

The wonderful thing about crystals is that they form amazing geometric patterns, sometimes perfect in shape. Thanks to The Helix’s reader, Billy Quist, you can grow your own crystals at home.

Warning: This activity involves boiling water and the use of a sharp object to punch a hole in the lid of a jar. Please find an adult to help you.

What you need

To do this activity you will need the following items:

a large glass jar with a lid a thin piece of string Blu-Tack (or similar) a sugar crystal 1 – 2 kg of sugar food colouring (optional) a saucepan.

What to do

Diagram of the Crystal Grower experiment.

1. Drill or punch a small hole through the lid of the jar (you may need an adult to help you). Thread the string through the hole. Secure the strand with a small ball of Blu-tack, covering the top of the

hole or alternatively tie a knot above the hole. Tie a good-sized sugar crystal (seed crystal) to the other end of the string.

Place ¾ cup of water in the saucepan, bring it to the boil and then reduce to a simmer. Pour sugar into the hot water until no more sugar will dissolve. If you do not add enough sugar, the solution will not become ‘super-saturated’. Turn off the heat and allow the sugar solution to cool. Don’t touch or move the saucepan, as the sugar solution will be extremely hot. Once the solution is cold, pour it into the jar until it is approximately ¾ filled. Poor the remaining solution into a spare container for later. Secure the lid, ensuring that the strand and sugar crystal are in the solution. Place the jar in a cool location, such as a cupboard. Check the crystal each day. If the crystal hasn’t grown for a day or two, replace the solution with remaining sugar solution, or make some more in a saucepan. The crystal needs to sit in a super-saturated solution to continue growing. Time and patience are required because crystals are slow growing. The crystals in the photo at the top of this page were growing for about a month. You may want to leave yours to grow for more than a month. The crystals will eventually reach a point where they will stop growing.

Once your crystal has become large enough, you can remove it from the string.

For added flair, add food colouring to the water to create colourful crystals. (A small drop of the colouring is sufficient.)

What’s happening

A solution is a mixture of a solute and a solvent. In this example, the solute is sugar and the solvent is water. If you add a small amount of solute to the solvent, typically the solution is under-saturated. Adding more solute will cause the concentration of the solution to increase, until you cannot dissolve anymore solute. The solution is now called saturated.

By heating the solution it is possible to dissolve more solute, making the solution super-saturated. This is an unstable state for the solution and as soon as conditions change (for example the temperature lowers), some of the solute will reappear in solid form – precipitation.

To precipitate, the dissolved solute looks for a ‘seed’ to build upon. In the case of our experiment, it uses the sugar crystal. Over time, more of the solute precipitates on the outside of the seed, layer upon layer, forming a

larger crystal. Once the solution returns to a saturated state, the crystal stops growing.

Creating a seed crystal

If you need a seed crystal large enough to tie on the end of your string, here’s an idea. Half fill a jar with water from the tap and stir in a few tablespoonfuls of sugar until the solution is saturated. Tie a piece of string to a pencil and balance it over the top of an open glass jar with the string hanging in the sugar solution. Place the jar in a sunny position and within a few days you should have a number of good-sized seed crystals.