Growing Alum Crystals

Growing crystals is a simple, rewarding pursuit! You have to feed growing pets, and water growing plants, but growing rocks is a hands-off activity. You can spend afternoons growing different kinds of crystals, and if you have a spare bookcase shelf or corner table, you can arrange the dishes and rocks to form a beautiful, eye-catching conversation piece.

Time required: A few days to a week.

School links: Chemistry.

What you’ll need:
-2 ounces of alum (you can find it in the spice section of supermarkets);
-One or two clear glass jars to grow your alum crystal in, and you might want a fancier glass bowl or dish for when it’s big enough;
-Nylon string
-A pencil
-A clean spoon;
-(optional) Food coloring;
-(optional, makes it easier) A clean pebble.

1. If you have a clean pebble, skip to step 8. This means you won’t have to grow a seed crystal first (which is missing part of the work, but also part of the fun of growing a whole crystal!).
2. Boil enough water to fill the container in a saucepan.
3. If you have food coloring, add a drop or two to your alum, and stir it well, so that all the little crystals are colored the shade you want (it may vary when the alum crystal begins growing, though).
4. Pour the hot water into the container, and stir in the alum, a bit at a time. If you get to the point where alum is sitting on the bottom of the jar, undissolved, stop adding more.
5. Cover the jar with a cloth and allow to sit undisturbed for a day. You can watch the crystals form, but don’t touch!
6. After a day or so, when the water has cooled completely, you should begin to see sizable crystals. Choose the biggest or best-shaped crystal (this will be your seed crystal) and remove it from the jar with a spoon. Be careful not to shatter it.
7. Place the seed crystal on a paper towel to dry out for a day.
8. Tie the nylon string around the pencil, and the other end to the seed crystal (or pebble).
9. Pour the alum solution into a clean jar and balance the pencil on top of it.
10. Cover the jar with a cloth to prevent dust.
11. Wait as long as you like while the seed crystal grows bigger and bigger. If crystals begin to form on the side of the jar, transfer the crystal on its string and pencil to a clean jar and pour the solution into it. If the color is fading, add a few more drops of food coloring to the water.
12. Once the crystal is big enough, you can either let it dry out and display it, or keep it in a dish or bowl of alum solution so it will keep growing.

Try experimenting with different colors in your alum. If you’re really bold, try using more than one color. You could see if transferring the seed crystal back and forth between the two colors to form a layered crystal works, or try some ideas of your own.