How to Make Rock Candy

How to Make Rock Candy

It's very easy to make rock candy, and it's a great science lesson in making crystals!

Rock Candy is essentially crystalized sugar. You create a saturated solution of sugar in water, and then insert a string with 'seed crystals' on it, and as the solution cools, the crystals form on the string.

The Recipe:

Supplies/Ingredients -  Glass or Jar, cotton string, paper clip, pencil, water, sugar.  Food coloring is optional.

Clean the glass or jar well.  Cut a length of cotton string (or several lengths) about the same length as the glass or jar is tall.  Tie one end to a paper clip.  Tie the other end to the middle of a pencil.  The pencil must be long enough to straddle the opening of the glass or jar.

Wet the string with water, and roll it in dry sugar crystals.  Set on a paper towel to dry while preparing the sugar solution.

Bring a pot of water to a boil.  Stir in sugar crystals, watching them dissolve.  Keep adding and stirring until the crystals no longer dissolve.

Once the water will no longer absorb any more sugar, you can add food coloring or other extract flavoring if you like.  Do not add very much flavoring, as some extracts will affect the crystalization process.

Let the solution cool for about 10 minutes.  Then pour it into the jar.  Lower the string (with the seed cystals on it) into the jar, paper clip first.  (The paper clip is to weigh the end of the string down.)  Suspend the string by hanging it from the pencil...twist the pencil to wrap the string until the paper clip is just off the bottom of the jar.

Place the contraption in a cool place where it will not be moved or shaken.  Crystals may appear as early as 2-4 hours.  If nothing happens in 24 hours, you probably didn't dissolve enough sugar in the water.

Remove the strings when the crystal formations are big enough to your liking.

Enjoy!

The Science:

Hot water is able to absorb more crystals than cold water.  When water is hot, the molecules bump into each other more frequently, causing them to 'spread out', creating more room between them for the sugar crystals.  When the solution cools, the water molecules move closer together, squeezing the sugar crystals back out.

The molecular structure of sugar causes it to bond to each other in a very symmetrical pattern.  Since there are some 'seed crystals' already present in the solution (on the string), when the solution cools and the sugar molecules come back out of solution, they naturally adhere to the existing structure.

I hope you enjoy learning how to make rock candy, and a little of the science behind it!