Weekend Project: Make Your Own Salt Crystal Tree

The main scientific principle that is at work here is capillarity or capillary action. This is the same process (involving microscopic tubes) that allows plants and trees to draw water and nutrients up from the soil, through their stems, branches, and trunks and into their leaves, flowers, and fruit.

*Thin cardboard (like the back of a notepad)

*Pen or pencil

*Scissors

*Ammonia

*Table salt (plain or iodized – either works)

*Mrs. Stewart’s Liquid Bluing (available in the laundry aisle at your local grocery store or online on amazon.com)

*Food coloring

*Measuring spoon (1 tablespoon)

*Small dish or bowl)

*Water

Use a pen or a pencil to draw two tree shapes on the cardboard. Each shape should be about 4 inches tall and 2 inches wide. Also, be sure to draw a notch half way down from the top on one shape and half way up on the other (as shown).

Since cardboard contains cellulose from trees (like all paper products), it draws up the growing solution in very much the same way. The tree sucks up the solution until it is completely soaked!

Use scissors to cut out both tree shapes, carefully cutting out each notch.

Slide notches together and position tree shapes so they are perpendicular to one another.

Put a drop of food coloring on each of the tree's branches and at the very top.

As the solution reaches the tips of the branches, some of the color from the food coloring also is dissolved into the solution.

Prepare the growing solution in a small bowl. Mix together 2 tablespoons each of water, table salt, liquid bluing, and ammonia. Stir thoroughly, until most of the salt has dissolved. You want to saturate the growing solution.

One the solution is prepared, put your tree in the bowl and watch as the growing solution begins to move up into the cardboard. Place your tree where it wonít be disturbed while it grows. Salt crystals are very fragile.

After the solution has been drawn up into the cardboard tree, it begins to evaporate. This process is sped up by the presence of the ammonia (which evaporates more quickly than water). When the water and ammonia evaporate, they turn from a liquid into a gas and the they leave behind the salt as small, white crystals (some of which are dyed by the food coloring).

You'll start to see crystal growth in about 6 to 8 hours with your tree looking like this after about a full day of growth. Notice how the crystals have picked up the color from the food coloring.

TIP: Don't worry if the growing solution turns a brownish, orange color from its original dark blue. This is a natural oxidation of the iron in the liquid bluing (like rust) and your salt crystals will still grow.

The tree after two days of growth.

These crystals form quickly and easily around the very, very small particles of blue powder (ferric hexacyanoferrate or Prussian Blue) that are suspended in the liquid bluing. (NOTE: in liquid bluing, the blue powder isn't actually dissolved it is suspended or floating in water.)

The tree after four days of growth. (I moved it to my windowsill to avoid it being disturbed on the counter!) Notice how the solution is almost all gone and the crystals have grown all over the tree and even on the edges of the bowl!

To keep your tree growing, make more of the solution from step/slide #6 and carefully pour it into the bowl.

A close-up of the fabulous salt crystals! It looks like coral!

In this fun experiment, no chemical reactions actually take place. All of the changes are simply physical, as dissolving and crystallization take place around the bluing particles over the course of time.

Jim Noonan is a former crafter for The Martha Stewart Show where he worked for four years both on-air and behind-the-scenes developing and producing numerous original craft projects.

He is also the founder of Professor Figgy's Fabulous Science Kits which creates unique and educational science kits for kids and families that combine the wonders of science with the fun of crafting. Jim is originally from Westerly, Rhode Island, and currently lives in Brooklyn.