It probably was before we were wecraftcards.com....
Here is a general set of instructions, I just paint the solution onto the paper and let dry. It looks like the ice forming on a puddle. (different types of salt create different sized crystals and ratios can be made saltier for a different look too!)
Cut the construction paper so that it lays flat in the bottom of the pan. Mix 1 tablespoon of Epsom salt into 1/4 cup warm water and stir until dissolved. Pour the salt solution over the paper. Place the pan in bright sunlight and as the water evaporates short, spiky crystals will appear.