It's easy to grow rock candy or sugar crystals. You can use any type of sugar. I used ordinary granulated table sugar (sucrose), but you could use brown sugar or some other type, if you prefer.
Bring 3 cups of sugar with 1 cup of water to a boil. This dissolves the sugar so you can grow big rock candy crystals. Once the mixture comes to a boil, remove it from heat. You can add a few drops of food coloring and 1/2 teaspoon of flavoring, if desired. Common flavors include cherry, lemon, mint or cinnamon.
Pour the sugar solution into a glass or jar. Hang a string or stick in the container so that it does not touch the sides or bottom of the container. Cover the container with a paper towel or coffee filter so the solution can evaporate, but won't get dirty. Allow the crystals to grow.
To get good crystals, you need to remove competing crystals that try to grow on the top, sides and bottom of the container. It's easy to break off the top crystals. You can eat them or throw them away. You need to transfer the string or stick to a new container if you see crystals growing on the sides or bottom. Just pour the solution into a new container and continue growing the rock candy.
When you are satisfied with the crystals, eat the rock candy or you can allow it to dry and save it for later. It doesn't go bad, but needs to be kept away from moisture or else it will get sticky.
Feel free to ask me any questions you may have. You can find more of my crystal projects at chemistry.about.com and my music over at Amazon as Azareal.