How Do Sugar Crystals Form on the String?

Making sugar crystals is a sweet way to learn science at home.

Making sugar crystals or rock candy is a tried and true, hands-on experiment to teach children about solutions and the processes of evaporation and wicking.

How Crystals Form

According to the Ask A Scientist web site, crystals form as a solid substance comes out of the solution. A solution is one substance dissolved in another. You can make a simple sugar solution by putting 2 cups of sugar into 1 cup of boiling water. Stir until the sugar is completely dissolved.

Evaporation Aids Crystallization

Crystals will form given enough time as the water evaporates, leaving behind whatever solid has been dissolved in the solution. In the case of the sugar solution, if you were to pour it into a shallow pan the sugar would form piles of crystals on the surface and sides of the pan.

Wicking Forms The Crystals on the String

Wicking is the process of drawing a liquid into an absorbent material. To form crystals on a sting, tie a clean small washer to the bottom of a piece of string. Then tie the string to a pencil. Place the pencil over a wide-mouth jar so the string is hanging down inside the jar. Carefully pour the boiling sugar solution into the jar and position the pencil over the center of the jar's mouth.

Sugar Crystals Take Time

Allow the jar to sit undisturbed for at for 14 to 21 days. The solution will be drawn (wicked) into the string. As the water evaporates, sugar will be left in and on the string. Due to the way the sugar crystals re-formed while in the boiling solution, the crystals that grow on the string will be larger than the sugar crystals used to make the solution.

References

• MiMi: Wicking
• Ask A Scientist: Growing Sugar Crystals
• Science Buddies: When Science is Sweet: Growing Rock Candy Crystals
• Crystal Growing: Recipes for Growing Sugar Crystals