Chemistry

How to Grow Crystals at Home



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Alum is a spice used for pickling, but has very little use as anything else.  But here’s one use you and your kids will love: growing crystals at home.  Ready?  Here’s what you’ll need.

Alum.  Water.  A bowl.  A piece of cloth to cover the bowl and a rubber band.  That’s all.  You probably have all of that at home.  Except for the alum, of course.  Very few people keep alum around.  But thankfully, alum is available in small, two ounce containers in the spice aisle of your local grocery store.

Now, heat four cups of water until the water starts to bubble.  Slowly stir in four ounces of alum.  Once that alum is completely dissolved, slowly continue to pour in alum and stir, until the alum no longer dissolves into the water.  It can take eight to ten ounces.  This will create a solution where the water is saturated with alum.  Pour the solution into a small bowl, like an empty and clean plastic butter container. 

Take the cloth and cover the bowl with it.  Use the rubber band to hold the cloth in place around the opening, so no part of it dips into the water.  Crystals will start to form in the first hour.  Keep the bowl covered in a warm, dry room.  Let sit for a day or two, until the water has dissolved leaving behind only the alum.  The alum will have formed irregular shaped crystals that may be as large across as a nickel.  They will range from a milky appearance to almost “crystal” clear.

For variety, try adding a few drops of food coloring to the water/alum mixture just before covering the bowl.  The alum will absorb the color and you can create red, green, yellow, or other colored crystals this way.

If you want to make larger crystals, take one or two of the crystals you have just formed, and repeat the steps above.  Once you have poured the water/alum mixture into the bowl, place the crystals previously formed into the solution, then cover with the cloth like before.  The new crystals that form will adhere to the crystals previously made, and create larger and larger crystals!  Crystals made this way will last for years and your children will love to show their treasures off to their friends.

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