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Substrate City: What Household Objects Form the Best Crystals?

based on 86 ratings
Author: Michelle Formoso

Crystals like to form on a substrate, or base surface of some kind; the texture, composition, and surface area of the substrate influences the formation of the crystals. Use four different household objects to see which ones form the most or best crystals

Problem:

Do crystals form more easily on some surfaces than on others?

Materials:

  • One bottle of alum (aluminum potassium sulfate, a pickling spice)
  • Disposable gloves
  • Very warm or hot water 500-mL beaker or glass measuring cup
  • Four large glasses or jars (that can hold at least 12 ounces)
  • Five coffee stirrers or craft sticks
  • Pipe cleaner
  • Rubber grommet or wide rubber band
  • Metal washer
  • Shiny push pin
  • Four eight-inch pieces of nylon monofilament thread or thin fishing line

Procedure:

  1. Put on your disposable gloves and fill the beaker or measuring cup with 400 mL of hot water.
  2. Sprinkle a little alum in the water and stir it with one of the stirrers until it dissolves completely. (Safety note: alum is a skin and eye irritant; always use gloves when you handle it, and don’t let it get in your eyes!)
  3. If all of the alum dissolves, add a little more and stir again. Keep doing this until it won’t dissolve any more. Now you have a saturated solution.
  4. Make a circle out of the pipe cleaner, small enough to fit into one of the glasses without touching the sides, and tie it to a fresh stirrer with one of the pieces of thread. Set the stirrer across the top of the glass so the pipe cleaner dangles inside.
  5. Carefully pour the alum solution over the pipe cleaner and set the glass where nobody will disturb it and it won’t get too warm (you don’t want the water to evaporate too fast and uncover the pipe cleaner too soon).
  6. Repeat steps 1-4 with the other objects.
  7. Optional: pick another small object to try in a fifth glass. Make it something that’s not too precious and that doesn’t either float or dissolve in water.
  8. Over the next several days, keep checking your solutions. Notice whether they form crystals at all or not, and if so, if they do it at different rates or about the same rate. Also, look closely at the shapes of the crystals. Do they look the same or different in each solution?
  9. After the crystals stop growing, you can take them out of their solutions to dry and display them!
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