The popsci website explains. You'll need some glass microscope slides, some runny-style 'superglue,' access to a fridge/freezer and a decent pair of tweezers. You won't actually be saving the snowflake, but making a 'fossil' of it. You chill the slides and runny superglue, tweezer your snowflake onto them, cover it, pop it in the freezer for a couple of weeks. By then the thin and runny glue will have flowed all around the tiny arms and holes in the snowflake and hardened. At that point you can take the thing out of the freezer. The snowflake itself will melt, but you'll be left with its imprint in all its detail.