Sponsored by Auburn University Montgomery and the Air Force Association


Students Instructions for Growing Alum Crystals

Crystals must be submitted by April 23, 2007


Step 1.
Record the date that the experiment begins. Place 1 heaped teaspoon of alum in a glass about ¾ full of very hot water from a tap. Stir the mixture until all the solid has dissolved. Add another teaspoon of alum and stir until it all dissolves. Continue adding small amounts of alum and stirring until no more dissolves and a little solid alum remains undissolved on the bottom of the glass.

Step 2.
Filter the warm solution into another glass. Cover the glass with a piece of cardboard or paper to keep out dust and set aside to cool overnight in a sheltered place.

Step 3.
Next day, the bottom of the glass should be covered with a layer of small crystals which formed as the solution cooled. Carefully pour off the clear solution into another glass, leaving behind the crystals. If no crystals have formed, let stand another day or so until crystals appear.

Step 4.
Select a single nicely shaped crystal at least 1/8 inch long and remove it with tweezers or a plastic spoon. This is called the seed crystal. If many crystals form together as a clump, a seed crystal can be carefully broken off. Save several large crystals in case they are needed later. Use a slip knot to tie a piece of thin thread tightly around the crystal. Tie the other end of the thread to a popsicle stick (or pencil) and suspend the crystal in the alum solution so that the crystal hangs about 1-2 inches from the bottom. Cover the glass with a piece of cardboard and place the glass in a draft-free area where it will not be disturbed (eg in a cupboard). Make sure your name is on the cup.

Step 5.
Over the next 2-3 days the crystal should more than double in size and take on the 8-sided shape of a typical alum crystal. Some crystals actually look like tiny diamonds! Remove the crystal, dry it with a tissue and measure its length (millimeters is a good scale to use). Record the date as well. Additional smaller crystals will probably have appeared on the bottom of the glass. At this point the alum solution should be warmed to about 50-60 BC to dissolve the crystals on the bottom. (Your teacher will instruct you about the method for warming the solution). Stir the warm solution with a plastic spoon to dissolve the small crystals on the bottom. This will probably take several minutes. When the crystals have all dissolved, let the solution cool back to room temperature (about one hour). Then suspend your crystal back in the solution and place it in a draft-free area as before.

NOTE: If the crystal is put back into the solution before it has cooled, the crystal may dissolve!

Step 6.
Repeat step 5 every 2-3 days to dissolve any crystals that may form on the bottom of the glass. Be sure to record the date and length of the crystal every few days. When only a few small crystals deposit on the bottom of the glass, the crystal's growth will begin to slow down. At this point, remove the growing crystal, warm the solution and add about a level teaspoon of alum. Stir to dissolve, filter and cool the solution. Return the crystal to the solution and continue to grow it. Repeat steps 5 and 6 until you are ready to stop the crystal growth.

Step 7.
When you have finished growing the crystal, remove it from the solution and dry it with a tissue. To help preserve the crystal, coat it with clear fingernail polish. It can then be handled occasionally with dry fingers. When dry, store the crystal in a zip-lock plastic bag.

Enjoy crystal growing!

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