How to Make a Salt Crystal GardenThis really easy. Mix equal parts table salt, household ammonia and iron(III) ferrocyanide solution. The iron(III) ferrocyanide is found as Mrs. Stewart's Laundry Bluing or as a common artist pigment, Prussian Blue. If you use the dry pigment, dilute it with water to make a deeply-colored blue solution. The exact measurements are not critical.
Pour the mixture into the bottom of a shallow dish. Set a cardboard tube (~4" tall) into the solution. The crystals are naturally white, but if you want some color you can dot the cardboard tube with food coloring or water soluble marker ink. The solution will creep up the tube. You'll start to see crystals forming within a few hours. Continue growing crystals as long as you like. I'd allow a couple of days for observations. These crystals are very fragile, so place the dish somewhere where it won't get bumped.
Salt Crystal Garden | Charcoal Crystal Garden