Friday, December 9, 2011

Grow a Crystal Snowflake

Grow your own crystal snowflake ornament overnight!  This activity is fast and simple and a great example of crystal growth and shape.  From our rock collection activity last week, the girls are fascinated by crystals.  (Crystals are sparkly and they are girls - what else can I say?)  Because rocks are combinations of multiple minerals, the crystals are not able to grow in their true form as they would given optimal conditions.  We can create those conditions by creating a solution of borax in water and providing a surface (pipe cleaner) on which the crystals can grow overnight.  This activity results in a crystal snowflake that can be hung in windows or as an ornament.  Please be warned that the resulting crystals do look like rock candy but they SHOULD NOT be tasted! 

Materials Needed (for one snowflake):
  • recycled glass jar - pasta jar works well; the larger the jar the bigger the snowflake
  • boiling water
  • food coloring (optional)
  • stirrer - wooden spoon, etc.
  • pipe cleaner
  • 12" piece of nylon fishing line
  • pencil
  • borax - powdered cleaning agent, found with the laundry detergent at the grocery store

Process and Pics:
Cut pipe cleaner into smaller pieces that will fit inside the mouth of your glass jar.  In nature, snowflakes are always six-sided crystals so you will need three pieces for each snowflake.

Twist the pipe cleaners together at the middle so that you have a six-sided snowflake shape. (Note: you could definitely do this with other shapes - I imagine red hearts would be really cute around Valentine's Day!)
Attach the fishing line to the top of one of the snowflake spokes.  Tie it at the middle in a double knot and then tie another knot at the top.  The resulting loop of fishing line will later serve as the hanger for the snowflake and crystals should not form on the nylon line.  The picture below shows the knots made with green yarn - note this is for visual purposes only - if this one were hung into the solution then crystals would form on the yarn as well as the pipe cleaner.

Boil enough water so that the glass jar is filled to within about an inch from the top.  Take note of how many cups of water this is because the amount of borax added will depend on the quantity of water.  Carefully pour the boiling water into the glass jar - this is an adult job!

If desired, add food coloring to the water in the jar.  We added about 4 drops for Maya's snowflake but the resulting crystals were not that colorful - more of the resulting blue color was from the underlying color of the pipe cleaner so you may need to add more.

Add borax to boiling water one tablespoon at a time, stirring to dissolve after each addition.  Because borax is slightly caustic, it is best if the adult measures out and adds the borax although you can let your child stir if you like.  You will need 3 tablespoons of borax for every cup of water.  After the last tablespoon is added, not all will dissolve - that is okay!

Use the loop to hang the snowflake from a pencil and lay the pencil over the top of the jar, inserting the snowflake into the solution.  It should hang in the middle of the jar.  If it is touching the bottom, you can carefully pull it up and either retie the top knot in the fishing line or use a clothespin to hold it at the correct level.  If it is too high, you can make an S-shape with another pipe cleaner and hang that over the pencil, attaching the snowflake shape to the S-shape to lower it.

Give your child time to draw the set-up in their science journal.  Sydney used my sample snowflake with the green yarn around it to trace around, which was a great idea!

Allow to sit for at least 8 hours or overnight for the crystals to develop. 

Remove the snowflake from the solution.  Rinse very quickly in cold water and place on a folded over paper towel to dry.  Hang and admire your snowflake!

What's Happening?
The borax (sodium borate) that is sold in grocery stores is in a powdered form but actually has a crystalline nature similar to salt and sugar.  Most crystals can be classified as one of seven shapes (or systems).  Given the right conditions, crystals will grow in the form of their distinctive shape.  Below is a picture of the seven basic shapes that crystals will grow into.  A few common examples: borax is monoclinic; sugar is hexaganol and salt (NaCl) is cubic.

In this activity, we we able to make those conditions happen by adding the borax to boiling water.  The hotter the temperature of the water, the greater the amount of borax that is able to be dissolved. The solution becomes "saturated" when it can't dissolve any more of the borax (solute) that you are adding.  For best results, we tried to make a "super saturated" solution - one that contains more of the solute that could be dissolved under the conditions.  (Remember that not all the Borax dissolved after that last tablespoon was added?)  As the solution cools, the water can hold less and less of the borax and the excess borax starts to crystallize out of the solution onto the pipe cleaner. 

Experiment with other types of crystals.  Both table salt and sugar will work, but they do take longer to grow (maybe a week).  Again, create a super saturated solution by adding your mineral to boiling water to the point where no more will dissolve in the water.  Alum, found in the baking good sections of the grocery story (its used in pickling), will also grow good crystals.  Here is a great list compiled by of other crystal growing experiments.  If you do grow more crystals then provide your child with a magnifying glass and a strong light and see if they can identify which of the 7 shapes they represent.

You can also build some models of the seven common crystal shapes.  I developed a crystal structure activity using gumdrops and toothpicks.  This would definitely work better with older kids, but Sydney and Maya both enjoyed building them with some help.  They are learning some of the geometry words, like "square", "cube", and "rhombus" at school, so if nothing else this was a great way to reinforce their understanding of those shapes.  If you want to build the shapes out of paper, Math Forum has a crystal activity where you print the shapes, cut them out, and attach them together with glue.  (And, I couldn't resist adding this: here's a recipe for homemade gumdrops, if you are so inclined!)

Need a Snow Day?And, of course, there a zillion things you can do for further exploration and fun with snowflakes.  I found a couple of really fun ones to share.  This tutorial from Instructables (one of my favorite sites ever) is great for cutting 6-pointed snowflakes out of paper.  Also, Snowdays from Popular Front is a fun virtual snow flake lab where you can design and "cut" your own snowflake, add a message to it, send it through email and share it with the pool of other snowflake designers.

Have fun with the science of crystals and snowflakes!


  1. Great minds and all that--I just made some crystal-covered Christmas ornaments with pipe cleaners in a sugar solution. When I made it according to the recipe, with 4 cups sugar to 2 cups water, the ornaments started growing crystals within a few days, and I took them out. I reused the solution and added more ornaments, and those took about a week before I pulled them out, but those crystals were bigger, and they were beautiful.

    Did you find that your crystals got gooped up at all by solution dripping down as they dried out? I gave my second batch a quick rinse by dipping them in water, and those crystals looked great.

  2. We need to try sugar crystals sometime soon! It sounds like your second batch was able to grow for a longer period of time, which may be why you got the bigger crystals. Do you think if you reduced the ratio of sugar to water you could get the bigger crystals without taking out the first batch? And, I did rinse our crystals, too, and it did seem to make them clearer.