The Great Rock Candy Experiment of '08

Last week we watched a new show on PBS called Nova Science Now. Simon watched the show pretty attentively and afterwards he asked if we could do science experiments here at home. We've had a few kids science experiment books sitting on the shelves at home waiting for the kids to express an interest, so we said "of course!"

A few weeks ago Simon was watching Zula Patrol (my favorite kid's show, along with Cyberchase) and they had a segment on "solutions" vs. "mixtures" so he told us he wanted to do an experiment that involved a "solution". So, we decided to make rock candy. I quickly found a recipe online and we got started last week.

We decided to make four of them in different colors so we boiled up some water and added more than 5 full pounds of sugar, carefully watching the sugar dissolve 1 cup at a time. We then separated it into glasses where we added colors. Then we used clothes pins to hang wooden skewers in the sugar/water solution. Then we set them aside to wait the alloted 7 days for the sugar crystals to form. Here's what it looked like the next day:

It's hard to tell from the picture, but it seemed that nothing was happening. So, we re-read the recipe and figured that we had "cured" the wooden sticks improperly. So, we removed the sticks, rolled them in sugar and let them dry overnight. The next day we re-boiled each glass and added 1 more cup of sugar before putting the sticks back in and putting them back on a shelf. This time we had dramatic results. The following day it looked like this:

And, the day after that it looked like this:

And then finally:

And this was only after three days. I think that adding that last extra cup of sugar drastically increased the growth of the crystals. In fact, one of the candies grew so big that it stuck to the side of the glass. When I tried to remove it I broke both the candy and the glass. Here's what they all looked like after removing them from their solutions and letting them dry:
And, finally, here are some shots of happy kids & parents eating their first science experiment:


In preparation for future rock candy experiments I cured a couple of dozen sticks and have put them in a ziplock bag in the freezer. This way we'll be all set to do it again many times over the next year or so.

So, our first experiment was not only a resounding success, but was very tasty too!

Here are the most important things we learned if you want to make rock candy:

1. Cure the sticks ahead of time. Let them soak in a hyper-saturated sugar-water solution for at least a few hours. Then take them out, roll them in sugar and let them dry for a day or so. This gives the sugar crystals a preliminary surface to attach to once the sticks are placed back in the final solution.

2. You need less water than you think you do. If, like us, you're using glasses that hold 1.5 cups of water each, you do not need to boil 1.5 cups of water per glass, but instead only 1 cup of water per glass. The volume of the water will increase considerably since you're adding 2 cups of sugar per cup of water. Next time we do this we'll follow the recipe more closely and only use 4 cups of water and 8 cups of sugar.

3. Getting a deep color takes a lot of food coloring. We used 5 drops of food coloring per glass and the solution turned a deep color, but the final product was more pastel and light colored. I'm not sure what the right amount is.

4. Next time we'll experiment with adding flavors. Ours turned out great, but they were really just sticks of sugar. Adding something fruity might be nice.

Oh, and regarding solutions and mixtures, Simon said something really funny the other day. He said: "A solution is when something dissolves in a liquid. If you put monkeys in water it is just a mixture because you can filter out the monkeys with a net."

Truer words were never spoken.