Growing salt crystals Points to check:

Growing individual crystals and crystal gardens has always been a favourite activity in science classes. It can be very rewarding if done properly or a disaster! Weeks of work can be lost with a temperature change or by adding water incorrectly.

Growing salt crystals
Growing your own salt crystals can be both fun and engaging. All you need is salt, water, a couple of jars, cotton thread and an icy pole stick.

The same procedure can be used to make sodium chloride or "alum" crystals. The best results come with experimentation.

1. Tie a reasonably large knot in the cotton thread about 1 cm from one end and suspend the thred from the stick in the jar so that it does not touch either the bottom or sides of the jar.
   
   If you already have a small salt crystal, you can tie the crystal onto the thread instead of forming a knot. Remove the thread from the jar and keep for Step 5.
   
   
   
2. Warm some water, to around 70 - 80°C. There is no need to boil it.
   
   
3. Add salt until no more will dissolve and stir to make sure the solution is saturated (that is, undissolved salt remains on the bottom of the jar).
   
   
   
   
   
4. Pour off the solution carefully into a clean jar, leaving the undissolved salt behind. This needs to be carried out quickly as crystals will start to form as the solution cools.
   
   
   
   
   
   
5. Carefully suspend the thread in the solution, keeping it away from the sides and bottom of the jar. Wetting the thread with solution may help. If the thread will not behave, try suspending the thread in a clean empty jar and pouring the solution into the jar.
   
   
   
   
   
   
6. This is the most important step! The best crystals are grown very slowly in a clean place, where you can keep the temperature constant. Window sills and dusty tables are out! Try the refrigerator. This is the first secret of growing big crystals. The second is to keep out dust with a lid or cover.
   
   
   
7. After a day or so, although the time can vary, small crystals should start appearing on the thread, usually around the knot. Pick the best looking crystal, square and big, and carefully clean off the smaller ones with the back of a knife, but don't cut the string. Replace the thread with your chosen crystal back in the solution. Keep cleaning the thread of unwanted crystals until you have the crystal you require.
   
   
   
8. As the crystal grows you may wish to knock off small side crystals growing on the main crystal. If you get them early they are relatively easy to scrape off.
   
   

Points to check:

• Do not allow the crystal to come into contact with the side or bottom of the container as it may combine with other crystals and be lost.
  
• Do not allow the temperature to vary. If the solution and crystal is allowed to warm up the crystal may redissolve in the solution. This is why window sills are generally not good places to grow crystals.
  
• Keep dust out, as crystals will form around the dust to the loss of your own crystal.
  
• Do not add water to top up the solution, as this will dissolve your crystal.
  
• If you are running out of solution and wish to grow an even bigger crystal, remove the crystal and add some warm water to your jar. Add only enough water, while stirring, to just dissolve any crystals on the sides and bottom. Allow the solution to cool before replacing your crystal in the solution. Keep checking your crystal to see it is not dissolving. If it is, remove it and remake a saturated solution before replacing your crystal in the jar.

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