We started with white pipe cleaners (I think any color would work, but you would see the color through the crystals). The girls made them into all sorts of random shapes. Then we tied yarn to them in order to suspend them in our Borax solution
The solution we used was boiling water to fill a pint sized mason jar and 1/3 C of Borax (per jar). The solution is really cloudy at first, but it clears up as the crystals form. We used a dowel rod to suspend the snowflakes in the solution over night. A couple of our snowflakes didn't seem to crystallize at the top, so I thought I would add more water. Not the best idea since it dissolved the crystals that were already there. So we left those over night again before pulling them out. You end up with crystals in the bottom of the jar too, and luckily they come out with hot water and a little downward pressure (I just used a butter knife to break them up).
After they were dry we hung them up on our light for wintery fun. For more complete instructions check out this site: http://deliacreates.blogspot.com/2011/01/snow-and-ice-activities-for-kids-part_11.html