Start a pan of boiling water on the stove.
Twist a piece of cotton string (or a pipe cleaner) around the middle of the stick. The cotton string should be long enough so when the stick is placed over the glass, the string will hang just short of the bottom. Wet the string with a little bit of water and roll it in sugar.
Lay the stick over the top of the jar so that the string hangs down inside the jar, but does not touch the bottom of the jar. When the water has started boiling, remove it from the heat and let the water settle.
If you want to add color or flavoring, do so now. Mix in the sugar one half cup at a time. Continue adding the sugar until it starts collecting at the bottom of the pot and does not dissolve even when being stirred. Pour the sugary syrup into the glass until it is about one inch from the top.
Place the glass somewhere it can sit for awhile undisturbed. (Do NOT refrigerate) After a day or so you should start to see crystal growth forming on the string. Leave the string in the solution until the crystals are big enough for your liking or they have completely stopped growing. Place the pencil over the jar and allow the string to dangle into the solution. Do not let the string settle or touch the sides of the glass jar.
Remove the string from the glass and let sit to to dry out.
After letting dry, wait till the crystal is formed and ready. You have a choice now to eat the rock candy or you can keep it.