Christmas Crystals

This project was actually a week in the making. You see, I was teaching kids about crystals. They take a while to grow, so we’ve been watching this experiment all week long and talking about our observations. But the result – beautiful Christmassy rock candy – is worth waiting for.

To begin, I asked Jay to build a cube out of his snap-together blocks. He quickly obliged.

“Today we’re going to pretend that these blocks are a crystal. A crystal is a bunch of atoms or molecules joined together to make a solid cube. It looks like these blocks,” I told the kids.

I put a few sugar crystals in my hand and showed the kids. “Can you look very closely at these tiny crystals? They’re shiny and hard and kinda square or rectangular.” The kids examined and touched the sugar crystals for a while.

Next, we put 1 cup of water into a pot and put it on a hot stove. We added a cup of sugar to the water. The kids watched as the sugar crystals dissolved into the water. “When we put the sugar into the water, the crystals break up,” I told the kids. We broke apart Jay’s blocks that had made a cube.

Then I asked Jay to rebuild his block cube. He took a block in one hand and started to connect it to another block. “Stop!” I said. “See that single block you’re holding in your hand? That’s what you need to start building your crystal, right? The same thing will happen with the sugar. Now that we’ve broken apart the crystals, they need something to help put them back together. They need what’s called a “seed” that they can grow from.”

We took a short dowel, dipped it into the sugar water and then rolled it in more granulated sugar. Those crystals will be the seeds from which the rock candy crystals will grow. We set that aside to dry.

Next, we added two more cups of sugar to our sugar mixture – three cups total to one cup of water. We stirred after each cup was added until the solution became clear again. Heating the solution gently helps the sugar crystals break apart and go into solution. But don’t boil the solution for more than a minute if necessary – it will start to turn into hard candy.

Finally, we had a saturated solution. That means we’d dissolved as much sugar as the water could hold and it was starting to re-crystallize. We turned off the heat and set the sugar solution aside to cool for about 20 minutes. I added a few drops of food coloring and some essential oil flavorings. We made a batch of red cinnamon candy for my spicy Allie and a batch of green wintergreen candy for my smooth Jay and a batch of yellow lemon candy for Emmie.

Once the solution was cool and crystals were beginning to form on the surface, I poured the solution into clean pint-sized glass jars. We took our dowels that had been rolled in sugar and placed a clothespin horizontally across the stick about ¼ of the way up. The clothespin will rest on the lip of the jar and hold the stick upright in the sugar solution without letting it touch the sides or bottom of the jar.

The dowels went into the jar and we began our vigil. Slowly, over the course of a week, we watched the sugar crystals begin to form on our dowels. Every day or two, I’d pull the stick out and break up the crystals that had formed on the surface of the solution. Those crystals would sometimes stick to the dowel and make beautiful jagged peaks.

Finally, when the crystals have reached the desired size, we removed the dowel. I let it drip into the jar for a minute or two, then laid it on a paper towel to dry.

Voila! Beautiful Christmas rock candy and a fun science project all about crystals. The kids were fascinated to see these intricate, shiny stones appearing out of nowhere from a liquid solution!