Rock candy or sugar crystals are especially good to grow because you can eat the finished crystals! The basic recipe for these crystals is:

• 3 cups sugar
• 1 cup boiling water

You can add food coloring or flavoring to the liquid, if you want. It's easiest to grow these crystals on a thick string hanging from a pencil or knife into the solution. For best results, remove any crystals that aren't growing on your string.

These crystals resemble diamonds, except they are much larger than any diamond crystals you're likely to see! Alum is a cooking spice, so these crystals are non-toxic, although they don't taste good, so you won't want to eat them. To make alum crystals, simply mix:

• 2-1/2 tablespoons alum
• 1/2 cup very hot tap water

Crystals should start forming in your container within a few hours. You can also grow these crystals on rocks or other surfaces for a more natural look. Individual crystals may be scraped off of the container with a fingernail and allowed to dry on a paper towel.

These naturally clear crystals are easy to grow onto pipecleaner shapes. Choose a colored pipecleaner or add food coloring to get colored crystals. All you need to do to prepare the solution is pour boiling water into your container and stir in borax until no more will dissolve. An approximate recipe is:

• 3 tablespoons borax
• 1 cup boiling water

These delicate crystal spikes grow in a cup in your refrigerator within a couple of hours, or sometimes more quickly. Simply mix together:

• 1/2 cup Epsom salt
• 1/2 cup very hot tap water
• food coloring (optional)

Place the cup in the refrigerator. Use care when scooping out the crystals to examine them, as they will be fragile.

Copper sulfate crystals naturally form blue diamonds. These crystals are extremely easy to grow. Simply dissolve copper sulfate into a cup of boiling water until no more will dissolve. Allow the container to rest undisturbed overnight. It's best to collect the crystals with a spoon or toothpick, since touching the solution will turn your skin blue and may cause irritation.

This project works with any type of table salt, including iodized salt, rock salt and sea salt. Simply stir salt into boiling water until no more will dissolve. The solubility of salt is highly dependent on temperature, so hot tap water is not hot enough for this project. It's fine to boil the water on the stove while stirring in the salt. Allow the crystals to sit undisturbed. Depending on the concentration of your solution, the temperature and your humidity you can get crystals overnight or it may take a few days for them to form.

Chrome alum crystals are deep purple in color. Simply prepare the crystal growing solution and allow the crystals to form.

• 300 grams potassium chromium sulfate (chrome alum)
• 500 ml boiling water

The solution will be too dark to observe crystal growth. You can check for growth by shining a bright flashlight into the solution or by carefully tipping the solution to the side. Don't spill! Disturbing the solution may slow your results, so don't check more often than necessary.

Copper acetate monohydrate produces blue-green monoclinic crystals.

• 20 g copper acetate monohydrate
• 200 ml hot distilled water

You can add food coloring to clear crystals solutions to turn them orange, but these potassium dichromate crystals come by their bright orange color naturally. Prepare the crystal growing solution by dissolving as much potassium dichromate as you can in hot water. Take care to avoid contact with the solution, as the compound contains toxic hexavalent chromium. Do not handle the crystals with your bare hands.