Magic Crystal Tree Experiment

The magic crystal tree is a crystal-growing project where crystals “magically” growing on a bare tree shape. It’s similar to the classic charcoal crystal garden project. The crystals are naturally white, but you can dye the liquid or the tree with food coloring to change the crystal color. So, you can grow white crystals on a green tree to resemble snow, turn a brown cardboard tree into a green or flowering tree, or add colored ornaments to a Christmas tree. It’s up to you! Here are simple instructions to grow a magic crystal tree, an explanation of how it works, and ideas to turn the project into a science experiment.

Magic Crystal Tree Materials

• 6 tablespoons or 90 ml water
• 6 tablespoons or 90 ml table salt (preferably uniodized)
• 6 tablespoons or 90 ml Mrs. Stewart’s liquid laundry bluing
• 1 tablespoon or 15 ml household ammonia
• Food coloring (optional)

The magic crystal tree requires basic household chemicals, plus laundry bluing. You may be able to find this ingredient at a store with laundry supplies or at a craft store. Otherwise, it’s readily available online. Laundry bluing is a mixture of the blue pigment “Prussian blue” and water. If you can’t find Mrs. Stewart’s laundry bluing, stir Prussian blue pigment into water or dilute Prussian blue acrylic or watercolor paint.

Prepare the crystal-growing liquid by mixing together all the ingredients. The crystals are naturally white. If you add food coloring to the liquid, all the “leaves” on the tree will be that color. If you want “snow” with “ornaments”, don’t add any food coloring to the liquid, but dot the tree shape with coloring.

Grow a Magic Crystal Tree

Sponge Crystal Tree

1. Cut a sponge into a tree shape.
2. Dampen the sponge and squeeze out the excess water.
3. Set the sponge tree in a shallow dish and pour the crystal-growing liquid over it.
4. Place the tree someplace it won’t be disturbed. Depending on temperature and humidity, you may see crystal growth within an hour and a complete crystal tree overnight.

Cardboard Crystal Tree

1. Cut two identical trees out of cardboard, card stock, or construction paper. Really, any paper works except waxed or other shiny, treated paper. To make the tree stand up on its own, make a cut halfway down the middle of one tree from top to bottom and halfway up the middle of the other tree from the bottom to the top. Match up the cuts to insert the bottom-cut tree into the top-cut tree. If you want Christmas tree ornaments or colored flowers, dot food coloring onto the tree.
2. Set the tree in a shallow dish and pour the crystal-growing liquid into the base of the dish. The amount of liquid in the base will decrease as it flows up into the tree, so if you have leftover liquid, you can save it to add when there is more space.

Make It an Experiment

Following instructions to grow a tree is enough to interest young explorers in science. But, it’s easy to turn the project into a real science experiment. To make the crystal tree an experiment, you need to control one variable (the independent variable) to see its effect on another variable (the dependent variable) and make a prediction about what you expect to happen (the hypothesis). Here are ideas of experiments to try:

• Change the amount of one of the chemicals and measure how it affects crystal growth. For example, you could see whether or not laundry bluing is really required to grow crystals. Another example is seeing whether changing the amount of ammonia affects crystal growth.
• See whether changing the size or height of the tree affects crystal growth. Remember to make a prediction about what you think will happen and record either how quickly crystals grow or how big they get.
• See whether adding more salt changes the size of the crystals.
• Test whether other common salts work in place of table salt. Examples of salts to try include Epsom salt, calcium chloride, or borax.

How the Magic Crystal Tree Works

The magic crystal tree demonstrates several science concepts, including evaporation, capillary action, saturation, and crystallization.

Pores in a sponge or gaps between fibers in paper allow liquid to flow via capillary action. The same process helps plants get water and nutrients from the soil up stems and trunks and into leaves. As liquid works its way to the surface, it evaporates. Ammonia speeds evaporation and helps the tree pull up liquid more quickly from the container. The crystals form from the salt and laundry bluing. Laundry bluing is a colloidal suspension of Prussian blue in water. More and more Prussian blue particles get deposited onto the surface of the sponge or paper and act as a nucleation site for salt ions to collect and crystallize. The salt starts crystallizing when enough water evaporates to form a saturated solution.

Safety

It’s safe to rinse crystal-growing liquid down the drain. Although the chemical name of laundry bluing or Prussian blue is ferrous ferrocyanide, the “cyanide” in the chemical name does not pose a health risk because it is tightly bound to iron. Similarly, this reduces potential toxicity from the iron in the compound. Still, avoid drinking the crystal-growing liquid or eating the crystals. Household ammonia is toxic, so it’s best to have adults mix and pour the crystal solution.

References

• Bakken, G.M. (2016). The World of the American West: A Daily Life Encyclopedia. Daily Life Encyclopedias. ABC-CLIO. p. 282. ISBN 978-1-4408-2860-7.
• Dunbar, K. R.; Heintz, R. A. (1997). Chemistry of Transition Metal Cyanide Compounds: Modern Perspectives. Progress in Inorganic Chemistry. 45. pp. 283–391. doi:10.1002/9780470166468.ch4
• Völz, Hans G.; et al. (2006) “Pigments, Inorganic” in Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH. Weinheim. doi:10.1002/14356007.a20_243.pub2