Place pieces of cardboard, charcoal briquettes and sponge in your plastic bowl. Make the pieces small, about an inch long. You can even cut cardboard into shapes like a flower or a tree to let your crystals grow like leaves or petals on the cardboard. These materials make up your substrate, or the material on which your crystals will grow.

Add drops of food coloring on your substrate. This step allows for colored crystals; any areas that don’t have food coloring will grow white crystals.

In a mixing bowl, mix the salt and water together with a spoon until the salt dissolves. Add the ammonia and bluing and mix until the ingredients are well blended.

Pour the mixture over the substrate. Some of the mixture will collect at the bottom of the bowl, but you will notice your substrate materials start to soak up the liquid.

Set your plastic bowl aside and allow it to sit undisturbed for 10 to 12 hours. When you return, you will see your crystal blooms have grown. The laundry bluing helps your mixture form these blooms rather than large crystal chunks, and the ammonia speeds up the evaporation process. The porous materials like cardboard and sponge pull the mixture from the bottom of the bowl to the top of the substrate pieces in a process called capillary action, much like a tree obtains water from the soil. As the water evaporates, the salt forms crystals.