Crystal Growth

by Jeremy Moody


A crystal is a solid with an orderly, repeating arrangement of atoms [1].

I found a book [2] with instructions for growing alum crystals. It said I was supposed to dissolve 3 tablespoons of alum in one cup of water, and cover the jar with plastic, and set it in a place where it would be undisturbed. I did this, and I waited for about 10 days, but no crystals grew.

Then I found some information [3] that said I wasn't putting enough alum in. It said to add 2 tablespoons of alum in 2 ounces of water. I changed this to 8 tablespoons of alum in 8 ounces (1 cup) of water. This was more than twice as much alum. When I tried this, it worked in only one day.

Once I was able to grow alum crystals by following the instructions, I was ready to start my experiment.


I did this experiment because I wanted to figure out what would happen if I disturb my jars while crystals are forming.


I think that the jar I shake will have crystals, but just not as many, or have the crystals scattered. The one turned I think will be just like the control. The stirred one will have grooves in it that go around in a circle. I also think it will have a little ditch in the middle of the grooves.


Alum (aluminum ammonium sulfate; you can get this in a drugstore)


4 empty mayonnaise jars


microwave (not a stove)

measuring spoons and cup

2 Lego motors, gears, axles, bricks, train track, baseplate

bin to hold everything in

foam rubber to keep the control and the shaken jar from vibrating

paper towels


I built a wall for one of the jars to go in, then I took the train track and put it on top with a motor. I also built a turntable out of Legos. I used lots of gears to make the turntable spin slower.

I had four jars for my experiment. For each jar I used 1/2 cup (8 tablespoons) of alum and 1 cup of water. I boiled the water and stirred in the alum until it dissolved. Then I put the four jars in the bin.

One of the jars I didn't disturb, which is the control. Another one I shook two times a day. The next one I turned with a motor on a turntable. The last one I spun a gear around with a motor.

Since I couldn't cover the stirred jar, I left all four jars uncovered during the experiment.

I covered the shaken jar only when I shook it.


One day after I started the experiment, there were crystals in at least three of the jars. I couldn't tell if the stirred jar had any crystals because the solution was cloudy. The one that got shaken looked exactly the same as the control before I shook it. There were crystals all over the bottom of both of them. The turntable one had crystals growing just around the outside of the jar and a few dusty lines going into the middle. I shook the jar that was supposed to be shaken really hard, and that made it look cloudy.

The next day I noticed that the crystals in the control jar were the clearest and the biggest. The crystals in the jar that was being turned looked a lot like the crystals in the control jar. The crystals in the shake jar were very tiny and not very clear. There were a few big ones that were clear, but most of them were tiny and not clear.

After one more day, I noticed that the jar that the motor was stirring was still moving but the gear was now above the crystal fluid. So I stopped the experiment.

Inside the stir jar there are crystals in a ring above the surface of the fluid, and some at the bottom with a swirly shape that looks like a lower case e.


I think that the crystals in the Stir jar weren't in a spiral shape with lines because the water was getting stirred around and it was making the crystals harder to grow.

My experiment shows that if you want to grow big, clear crystals, you shouldn't disturb the solution.


1. Holden, Alan, and Morrison, Phylis. Crystals and Crystal Growing. Cambridge, MA: MIT Press, 1982.

2. Kenda, Margaret, and Williams, Phyllis S. Science Wizardry for Kids, p. 48. New York: Barrons, 1992.

3. Hoyt, Kay. Iowa 4-9 Science Project.

February 26, 1998

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