If you found an ad for this instructable in the back of a comic book, it would read something like:
"Amaze your friends by growing a crystal tree out of common table salt and a few other ingredients available from the grocery store"

Step 1: Gather Your Materials

Gathering the ingredients is probably the most difficult step. To grow your Magic Crystal Tree, you'll need:
- Mrs Stewart's Bluing
- Table salt
- Household Ammonia (the kind with no soap added)
- Cardboard (not corrugated)
- Bowl
- Water
- Measuring spoon
- Food Coloring (optional)

The bluing is the hardest item to find but can be found in the cleaning section of many grocery stores. You can find the ammonia close by.

The cardboard I used came as packing material from a new shirt, or the backing from a paper notepad. Cereal box cardboard might work, but it's thinner & has printing on one side...

Depending on the temperature & humidity of your location, the ammonia is optional, but speeds up the crystal growth -- the tree in this Instructable started "sprouting" in less than an hour. Without ammonia, it may take a couple of days to start.

Step 2: Cardboard Shapes for the Crystals to Grow On

For this Instructable, I made a tree formed out of two cardboard triangles, roughly 2" at the base and about 3.5" high. If you'd prefer some form of unspeakable tentacled beasty, send me a picture!

Cut a slot from the top to the middle in one piece, and from the bottom to the middle in the other. The slots allow the two pieces to be assembled into a 3D shape.

Make sure that whatever shape you create can stand up by itself.

Step 3: (Optional) Color the Tree

If you like, you can add a little color to your shape by putting drops of food coloring on the edges. The food coloring will soak into the cardboard.

Step 4: Adding the "Magic" Solution

The "Magic" Solution -- Mix together:
- 1 tablespoon water
- 1 tablespoon salt
- 1 tablespoon bluing
- 1/2 tablespoon household ammonia

I put everything into a small bottle that could be shaken to mix the ingredients.

Again, the ammonia is optional, but I'd recommend it.

Find a place where you can watch your magic tree grow undisturbed for a few days.

Put the tree into the bowl and add the solution

Step 5: Wait...

Wait...

Wait a little longer...

More waiting...

(First sign of growth showed up at around the one hour mark...)

Step 6: Time Passes

The tree after 12 hours.

You can keep your crystal shape growing indefinately, by adding more water/salt solution to the bowel.

Step 7: What's Going On?

The salt solution is wicked up into the cardboard tree via capillary action. Water evaporates from the surface of the tree, forcing the salt to crystallize out.

Mrs. Stewart's Bluing is a colloid -- tiny particles suspended in water (think of glitter in a snow globe, but much, much smaller). The tiny particles make it easier for the salt crystals to form.

The ammonia helps speed up the evaporation process, which makes the crystals grow faster.

There's a more detail explanation available from Mrs. Stewart's Bluing at http://www.mrsstewart.com/pages/explanation.htm

Step 8: Filming the Crystal Tree Growing

I set up a Canon PowerShot A40 with remote capture software to take one picture every minute.

The halogen desk lamp overhead is an attempt to provide a consistent light source, as well as warming things up a little (to speed up evaporation).