Ask an Expert: Growing Crystals

[nickielinton]

I am doing an experiment for a Science Lab class in college. It is a simple experiment of which material will sugar crystals grow the best on, cotton, wood, plastic, or metal. My question is... what causes the sugar crystals to form on an object? I understand, and can find plenty of research/answers on "how" they form, and "why" they form, just not why they form on a certain object. I guess what I'm asking is what makes them attracted to the material in the first place to start growing there? Why cotton string? Why a wooden stick? Why doesn't it choose the side of the glass jar? Why can the material not be touching the bottom of the jar during the experiment? I can't find answers to any of these questions. Can you help me out? Do you have the answers? Can you give me links to articles that explain these things? Any help would be greatly appreciated!

[charlesg]

Hi nickielinton,

To start growing, crystal growth usually requires a "crystal seed": a sucrose clump, small particulates, or air. The string likely introduces small air bubbles or dust that can serve as crystal seeds.

Other ScienceBuddies users have actually had issues growing rock candy and ended up with sugar crystals on the sides of their jar. This could have to do with a slightly dirty jar or disturbing their supersaturated solution too early.

For more information, ACS has an article on different sugar candies: https://www.acs.org/content/acs/en/educ ... aking.html

Best,
Charles

[nickielinton]

Thank you!