Oct. 21, 2011

Science Dad on Crystals, Part Two

by Vince Harriman

Click to enlarge images

After last week's project arranging blocks to understand crystal patterns, we decided to grow some crystals to see exactly what they look like. For today's project, we decide to grow salt crystals -- a fairly easy and rewarding project that can be tackled at a fairly young age with the proper supervision. I was particularly excited about this project because I did it when I was Beckett's age. To grow a crystal salt garden, you need the following supplies:

  • 3 tablespoons Bluing (available at most grocery stores and some drugstores or hardware stores)
  • 1 tablespoon Ammonia
  • 3 tablespoons Salt
  • Non-porous container
  • Charcoal briquettes, sponge, toilet paper roll, light wood (such as balsa or pine)
  • Safety glasses
  • Optional: gloves, apron and newspaper

Begin by preparing the area-if you are worried about spills or have light countertops you'll want to put down some newspaper. Carefully combine ingredients in a pyrex or suitable container and be sure to wear your safety goggles:


Beckett adding ingredients together

Beckett began by carefully adding bluing on top of the salt. We had Halite-rock salt crystals -- but any salt will do. We stirred this mixture then added the ammonia and stirred for about five minutes. We wanted to be sure that as much salt dissolved into the solution as possible. We could see the rock crystals getting smaller -- you will have undiluted salt, which is good. It means you have a super saturated solution.

Next we set up our growing area. The crystals will be super fragile so you'll want to find a place that they won't be disturbed. We set up ours in the basement. Beckett added the solution to the charcoal, carefully pouring the solution over all the charcoal and getting everything covered in the solution:

Pouring the solution

We didn't have to wait long to see crystals growing. Within just a couple of hours our charcoal was turning wispy white with salt crystals:

You can see the crystals just spring out of the charcoal and after about 24 hours we had a lot of crystal growth. What Beckett and I found interesting was that we had different types of crystals growing in different locations. We had a lot of pillowy white blooms that looked like cumulus clouds:

Cloud like crystals growing on edge

But right next to the pillowy white blooms we had yellow tree-like crystals:

Salt 'trees'

The crystals that grew on the small broken pieces of charcoal in the solution looked different from all the other crystals:

Crystals growing near the solution

I asked Beckett to come up with some theories to explain the diversity of crystal types. We had several ideas -- changes in the weather and specifically humidity; the proximity to the solution; whether or not it was new growth or growing where a crystal had already broken off.

We turned off the time-lapse video but let the crystals continue to grow and after another 24 and 48 hours, the charcoal tower was completely transformed with a variety of crystal types:

final crystals

And these types:

final results

These last two photos are great because you can see the different types of crystals growing side by side. Can you think of any reasons why salt would crystallize in different arrangements? As always, we love to hear from you-please leave theories (or answers, if you know) in the comments below. And if you have grown any crystals please let us know about that too.

About Vince Harriman

Science Dad, AKA Vince Harriman, is a freelance writer living in Annapolis. His two sons, Beckett-6 and Rowan-2 1/2 ask him 'why' approximately 6,542 times a day.

The views expressed are those of the author and are not necessarily those of Science Friday.

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