How to Grow Crystals

A crystal is a substance that has a highly ordered internal structure. Crystals can be composed of atoms, molecules, or ions.

Examples of common crystals include sugar and salt. Most gemstones are crystals, such as diamonds, emeralds, and rubies. Some materials that are called 'crystal' but really aren't include all types of glass and faceted plastic. Crystals can be shaped or cut, but their internal repeating structure often gives them a characteristic shape without any treatment.

[Photo: Quartz crystals (William Roesly, www.morguefile.com)]

Crystals that you can grow at home are grown from solutions in water. To grow a crystal, you dissolve a chemical in water, then either evaporate the water or cool the solution so that the substance starts to crystallize. Usually you hang a string or a seed crystal in the growing solution to provide a surface for the crystals to form. You want water to be able to evaporate from the solution, so you can't seal the container. However, you can place a coffee filter or paper towel over your solution to keep it clean. Crystals grow best if they are undisturbed. You can watch them grow, but don't pick up the container or shake it.

There are many types of crystals that you can grow, including some that come from foods. Even young children can grow these crystals. The crystal solutions start out very hot, however, so adult supervision is important.

Alum Crystals

1. Pour 1/2 cup of hot tap water into a clean jar. Boiling water is even better, but you don't absolutely need it, so if you're doing this project with younger investigators, feel free to use tap water.
   
2. Stir in alum (located on the spice aisle of the grocery store as a pickling ingredient) until no more will dissolve ( this can be up to 2-1/2 T).
   
3. Let the jar rest undisturbed overnight or for several hours.
   
4. Pour the liquid from this jar into a clean jar. Try not to get any undissolved solid material in the new jar.
   
5. There will be crystals on the bottom of the original jar. Select the best of these and tie a nylon fishing line around it.
   
6. Hang the crystal in the second jar so that it is covered by the liquid, but not touching the bottom or sides of the container.
   
7. Allow the crystal to grow until it stops growing or until you are pleased with it.
   
8. Remove the finished crystal and allow it to dry.
   

Salt Crystals

1. Add salt to boiling hot water until no more will dissolve. The temperature is important, since much more salt will dissolve with even a couple degrees hotter water.
   
2. For fast crystal, soak a piece of cloth or cardboard in the salt solution, then set it in a sunny, dry spot to dry. Numerous tiny salt crystals will form on the surface of the cardboard.
   
3. For larger crystals, you need a seed crystal. Get a seed crystal by pouring a small amount of this solution onto a saucer. Let the liquid evaporate. Carefully scrape the best crystal from the saucer and attach it to a nylon line.
   
4. Tie the other end of the line to a pencil or butter knife and hang the crystal in the growing solution.
   
5. The best salt crystals take several days to weeks to grow. Allow the solution to sit undisturbed in a cool, dry location. Remove the crystal when you are pleased with it or when it stops growing.
   

Sugar Crystals or Rock Candy

1. Stir 3 cups of sugar into 1 cup of boiling water. Keep stirring until as much sugar has dissolved as possible. You can add food coloring to the solution if you like.
   
2. Pour the solution into the container you have selected for growing the crystal. Avoid getting any undissolved sugar in this container, since the sugar will provide a growing surface for the crystals, causing them to grow on your container.
   
3. Suspend a wooden skewer or rough string into the solution.
   
4. Allow the solution to sit undisturbed.
   

[Photo: Sugar crystals or rock candy can be colored with food coloring and can be eaten. (Douglas Whitaker, wikipedia.org)]

There are three main problems you may encounter with your crystals.

Impurities

If you have an impurity (e.g., dishes weren't quite clean, chemicals weren't pure, or possibly you made a mistake with a chemical), your crystals may not grow or else they might not look like you had expected. There isn't much you can do to fix this problem except to start over, but before you do, eliminate the other main causes of problems.

Solution Not Saturated

Usually crystals don't grow because there wasn't enough crystal material dissolved in the water. You can concentrate an existing solution by increasing the rate of evaporation of the solution. The best way to achieve this is by improving the air circulation around the crystal solution. Placing the solution near a fan would work, for example. Lowering the temperature of the solution may help, too. This doesn't speed evaporation, but sometimes crystals will fall out of solution as it becomes cooler. Try refrigerating your crystals.

Undissolved Material

Another common problem you may encounter is crystals growing on the bottom of the container and not on your string. This occurs when the solution contained undissolved material. One way to lessen the chance of this happening is to filter your solution through a coffee filter or paper towel.