Prepare your tray or shallow bowl by greasing the edges with Vaseline. This step prevents crystals from growing over the edge. Place a few small pieces of charcoal briquette or a porous brick on the tray or in the bowl.
Measure the salt into a mixing bowl before adding the water. Stir to dissolve the salt completely before adding the liquid bluing and ammonia.
Arrange the charcoal briquettes evenly on the bottom of the tray for best results. Pour the salt mixture over the charcoal, being careful to saturate each one. Discard any lumps of salt that did not dissolve. Dab a few drops of food coloring directly onto the charcoal or omit the food coloring if you want natural color crystals.
Place the tray in a cool, ventilated area. Crystals need free circulation of air to form. Formations develop better when the air is cool and dry.
Add more salt, bluing and ammonia mixture after the initial crystals form to keep it "growing."
Be careful not to damage the delicate crystals when adding the mixture. It will bloom indefinitely with care and attention.