It only takes a spark to start a fire, and it only takes one atom to act as a seed for crystal formation. Under the right conditions, the atoms in alum will join together like puzzle pieces to form large crystals. I posted a few years ago about how to grow a large alum crystal, but this experiment is even more fun. It’s also easier for young kids, since it takes less small-motor coordination.
Alum is also called potassium aluminum sulfate. It’s used in pickling and in found in baking powder. You can grow beautiful alum crystals at home with a few jars of alum, water and any object you don’t mind covering with glue. We made fake geodes by breaking eggs in half and washing them out, but we also encrusted a grape stem and a plastic shark.
To do this experiment, you’ll need glue, 3/4 cup alum from the spice section of the grocery store (4 or 5 small jars should do it,) water and whatever you want to coat with crystals. It takes three days to complete.
On day one, paint glue on the objects you want to grow crystals on. If you’re making “geodes”, apply a thin layer of glue to the inside of an eggshell that’s been cut in half, washed out and dried. Then, sprinkle a little alum powder on the glue and let it dry overnight. We heavily coated our object with alum, but might have grown larger crystals if we’d used less. Each alum particle acts as a seed for crystal growth. The closer together they are, the less room your crystals will have to grow.
On day two, dissolve 3/4 cup alum in 2 cups of water by boiling. This step requires adult supervision. Make sure all the alum dissolves (it may still look a little cloudy) and let the solution cool. This is your supersaturated alum solution.
After about 30 minutes, when the solution is cool enough to be safely handled, gently immerse your object in the alum solution. For color, you can add a large squirt of food coloring. Let your project sit overnight to grow crystals.
On day three, gently remove your object from the alum solution and let it dry. How does it look? Draw it or take a picture to put in your science notebook!
Crystals are geometric networks of atoms. Imagine a three dimensional chain-link fence, and you’ll get the picture. Certain crystals will only grow in certain shapes. For example, diamonds are always cube-shaped when they form. Whether the atoms have joined to form a small diamond, or a large one, it will always be in the shape of a cube!
Some crystals, like alum, will form from supersaturated solutions, like the one you used in this experiment. A supersaturated solution is one that is forced to hold more atoms in water (or another solute) than it normally would. You can make these solutions using heat or pressure. Crystals can form when a supersaturated solutions encounters a “seed” atom or molecule, causing the other atoms to come out of the solution and attach to the seed.
What else could you try? Could you do the same experiment with salt, or sugar crystals? How do you think the color gets incorporated into the crystal? Do you think the food coloring disrupts the shape? Will larger crystals grow if you let your object sit in the solution longer?
You can read more about crystals and gems here.
Imagine pieces of matter (too small to see) called atoms that will only fit together in a certain way, like a puzzle. These atoms can attach to each other to form small three-dimensional shapes, or larger ones, but the shape will always be the same, depending on what kind of atoms make up the “puzzle pieces.”
This is what happens when crystals are formed. Diamonds and salt, for example, are crystals shaped like cubes, while quartz crystals are formed in trigonal shapes, sort of like three-dimensional kites. You can have very small diamonds, or huge ones, like the Hope Diamond, which is as big as a silver dollar and blue from impurities in the stone, but they will all have the same basic shape.
We grew alum crystals in a jar last week and I am amazed at how beautiful they are. I couldn’t get a very good picture, but they look like a string of real gems and were simple to grow.
To grow these spectacular crystals, you will need a small jar of alum, which can be found with the spices at the grocery store, water, a glass, a jar, a stick and some thread.
Fill the glass with about 3/4 cup of water and add a few teaspoons of alum powder. Stir until the powder dissolves and repeat until no more alum will dissolve and you can still see some floating around in the glass. Then, let the glass sit overnight or until some small alum crystals form in the bottom or on the sides of the cup. It took two days for us to get some decent crystals, but we got several small ones that were fun to look at!
Fish a large crystal out of the glass with a spoon and tie a thread around it. Tie the other end of the thread around the stick (we used a BBQ skewer) and wind it up so that you can rest the stick over the mouth of the jar and the crystal will hang down about half way. Then, pour the remaining liquid from the cup into the jar. There is still alum in the water, which will add more “puzzle pieces” to the crystal and make it grow bigger.
Now you can watch your crystal grow. What shape is it? Look at your crystals under a magnifying glass. Take a picture of them, or draw them your science notebook! Here is a link to a great Smithsonian website where you can learn more about gems and crystals.
We were up at the lake last week when the ice went out. It was amazing. We arrived at noon to a lake whose surface was half covered with ice and woke the next morning to clear water. The wind was blowing the ice into shore and it broke into millions of crystals that sounded like a field of windchimes. The crystals were so sharp that our dog cut his foot.
If you’re interested, you can watch the very wobbly, but cool video I took of the ice blowing around. You can see the ice crystals being pushed up and out of the water into piles. Listen, and you’ll hear the ice crystals clinking together!
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This week, the kids and I are going to grow alum and sugar crystals, so be sure to check for the upcoming post!