Making rock candy is a fun and easy experiment to do with your kids while teaching them a little bit about chemistry and a lot about patience. Plus, there’s a sweet reward at the end. Candy making usually involves thermometers and lots of corn syrup. Not so with rock candy! You just need sugar and water and although you could use a thermometer, you need not be so accurate.
There are many contraptions to this simple experiment. In general, it involves suspending a weighted string or wooden skewer in a glass with the sugar solution. I like to use a short cocktail glass and toothpicks stuck in a piece of wire mesh screen. It’s less time consuming to set up and you can make several small sticks of rock candy per glass. You can find the wire mesh screen in rolls at Home Depot for under $8. Besides serving as a toothpick holder here, these mesh screens have many other uses such as lining the bottoms of your plant pots, repairing window screens, and patching wall holes. In other words, they are handy to have around the house and well worth the $8.
To make the sugar solution, start with:
- 1 part water
- 2 parts sugar
by volume. I.e., one cup water to two cups sugar.
Sugar crystals after one week.
Directions:
- Heat the water in a saucepan until just boiling.
- Add the sugar and stir continuously until all the sugar is dissolved. Optionally dissolve extra sugar, a spoonful at a time. A well saturated sugar solution speeds up the crystal growth. If you add too much sugar and not all is dissolved, simple add a little bit of water at a time.
- Let cool a few minutes, occasionally stirring.
- Pour the mixture into clean, dry glass.
- Dip toothpicks in the sugar solution and roll them in sugar. Let dry. These tiny ‘seed’ crystals jump starts and accelerates the crystal growing process.
- Cover glass with prepared toothpick in mesh screen and wait.
- And wait and wait and wait. It will take at least a week for the crystals to grow to a good size.
- If you want to add food coloring or flavoring, add it after the first week when sizable crystals have formed. Otherwise, it will take much longer for the crystals to form. Let the crystals grow for at least another week.
At first, the kids were super excited and would check on the rock candy every day. By the second week after adding the color and flavor, they almost lost all interest after I told them they had to wait at least another week before they can eat it. But the longer they wait, the bigger the candy and well worth the wait!
Rock candy is just one of many experiments to show how crystals grow. Here are a few sites that explain the science behind it.
