Alum Crystals

Jasper wanted to learn more about crystals.  One of our library books told us how to grow alum crystals, and it was such an easy and fun experiment, I wanted to share it.  Alum is a class of chemical compounds that are used for lots of things, including giving baking powder its slight metallic taste and pickles an extra crispness.  And they love to form crystals!  The easiest place to find alum is in the spice section of a grocery store, but you will probably get twice as much for the same price by ordering a jar of it from a drug store.  (It's probably yucky anyway, but don't let your child actually eat it.)

First, your child can make small shapes out of wire for the crystals to grow on.  (One of our favorites was a spring shape made by twisting the wire around a pencil.) Then attach a short piece of fishing line to each wire shape and tie the other end of  the fishing line to a pencil or chopstick.  Place the pencil or chopstick above the opening of a jar.  You will want to suspend the wire shapes in the jar in the middle of the alum solution, so that the wires are not touching the bottom  of the jar.  

To make the crystals, take 11 Tablespoons of alum powder and dissolve it in 2 cups of water over heat.  My book said that it will dissolve at about 150F.  Then pour it into the jar.  When it cools to about 120F, it is important to slow down the cooling process.  I wrapped our jar in a towel and put it inside a cooler.  Keep checking it to see the crystals form.  Once the  wires have some lovely crystals growing all over them, you can take the wires out and hang them up to dry.  It took ours about 5 hours to form lots of nice crystals, and was really fun to watch.  But don't forget about them.   If you do, the crystals will grow large and heavy, and will fall off the wires.  

Be sure to have a magnifying lens on hand to examine the resulting crystals.  They are quite an interesting shape.  Your child can compare that shape to the shape of salt and sugar crystals.  Have fun!