Crystal Growing

Crystals are all around us. We looked at some different crystals that you might find at home.

salt crystals
sugar crystals
sand crystals

Alum crystals

Alum (potassium aluminium sulfate) grows crystals really quite quickly - over just a few hours - and has the advantage of being pretty non-toxic. It is used in pickling vegetables and as an ingredient in some toothpastes.

alum crystals

To grow nice alum crystals, we made a saturated solution of alum by stirring powdered alum into very hot water until no more would dissolve.

We poured the solution into a plastic dish (shallow saucers or large plastic lids also work well). Then we let it cool down slowly away from draughts and dust.

The crystals we grew looked hexagonal, like these on the left. (They are not regular hexagons because all the sides aren't the same length.)

Borax crystal ornaments

Borax Ornament
These are even prettier in real life!

Borax is a chemical used in detergents, amongst other things. Its full name is sodium tetraborate decahydrate. Lots of American children make borax crystals as it is sold in most US supermarkets as a household cleaner/laundry booster. It is harder to get hold of in UK shops, but you can buy it online (try ebay!)

It comes as a white powder like washing powder. Just like washing powder, you do NOT want to eat it.

Borax is very soluble in hot water - so lots and lots of powder will dissolve. It is not very soluble in cold water. So as the solution cools down, the borax wants to come out of solution.

Crystals start growing by a process called "nucleation". Nucleation can either start with a few borax molecules 'sticking together' themselves, or with the help of something solid already in the solution.

If you make a shape out of a pipe cleaner and hang it in the crystal solution, the borax molecules will tend to 'stick' to the pipe cleaner. Crystals are likely to start to grow on the pipe cleaner shape (scientists say that the pipe cleaner acts as a nucleation site).

The borax should start to form tiny crystals on the pipe cleaner after just a few hours. Over time these crystals grow larger and larger.

We all made different shapes out of pipe cleaners and left them in borax solution overnight. Crystals grew all over the pipe cleaners - by the morning the crystals were about 2mm-8mm across. The crystals are translucent (this means they let light through) so that you can see the colours of the pipe cleaners through the crystals.


Making Borax Ornaments

What you'll need:

  • An adult to make up the borax solution!
  • Pipe cleaners
  • Cotton thread or thin string
  • Lollipop stick or pencil
  • Borax
  • Boiling water
  • Clean glass jar(s) or plastic container(s) large enough to submerge ornament

What to do:

  1. Make a shape for your ornament out of pipe cleaners - you can make spirals, hearts, circles, diamonds, letters... just use your imagination.
  2. Tie one end of your string to the top of your ornament and the other end to your lollipop stick.
                Please get an adult to do the remaining steps:
  3. Mix up the crystal solution at a ratio of 3 tablespoons of Borax to one cup of boiling water. Stir until the Borax dissolves. Don't expect all of the powder to dissolve, some may settle on the bottom.
  4. Pour the crystal solution into a wide mouth glass jar or plastic beaker. Wear rubber gloves to be on the safe side!
    You will need enough of this solution to submerge your pipe cleaner ornament. Use several jars if you want to make more than one ornament.
  5. Submerge your ornament in the borax solution with the lollipop stick resting on the lip of the jar so that the ornament is completely covered and hangs freely.
    You do not want the ornament to touch the bottom of the jar.
  6. Allow the jar to sit in an undisturbed location overnight.

  7. These are our crystals starting to grow

  8. Take your finished ornament out and dry it on some paper towel. Dispose of the crystal solution carefully.


Some pictures of our crystals

borax crystals

We hung our crystals up in front of the window at school, they are beautiful and sparkly.

More science to try at home

If you have tolerant parents and enough patience to wait a few days, try making rock candy (crystallised sugar on a stick). It is a great experiment as you can eat the results!! Please note that the crystals do take a while to grow.

There are some good instructions for making rock candy here:

How to make your own rock candy