Experiment 3: Magic Salt Crystal Garden

What you need.

  • A tray or shallow bowl.
  • Vaseline.
  • Charcoal briquettes or porous brick or sponge.
  • 90ml table salt.
  • 90ml Mrs. Stewart's Liquid Bluing (sometimes found in soap section of the grocery store).
  • 15ml household ammonia.
  • Food coloring.

What to do.

Grease the edges of the pan with Vaseline to prevent crystal growth over the edge. Place a few pieces of charcoal briquettes or other base material in the pan. Mix the salt, liquid bluing, and ammonia together. Pour the salt mixture over the charcoal. Dab drops of food coloring on top of the charcoal.

A beautiful flower-like growth should should appear after a day or two. A free circulation of air is necessary, and formations will develop best where the air is dry.

To keep it growing, add more bluing/salt/ammonia from time to time. Be careful not to damage the delicate growing crystals when adding more salt mixture. It will "bloom" indefinitely into beautiful rosebuds, coral and crystals.

What can be learned.

The crystals are formed by salt molecules joining together as the liquid evaporates into the air. The ammonia helps to speed the rate of evaporation. Liquid bluing is a colloidal suspension of extremely minute particles of blue powder (Ferric Hexacyanoferrate). This is not a solution in the true chemical sense of that word. Ferric Hexacyanoferrate is an inorganic polymer of complex ions which gives bluing its blue color. The ammonia in the recipe breaks this complex allowing iron salts to be incorporated into the salt crystals growing in the crystal garden. Notice that when the ferric hexacyanoferrate complex is broken, the blue color is lost and the garden exhibits the reds and yellows typical of the original iron compounds that made up the bluing.

The purpose of the porous material (charcoal or sponge pieces) is to provide a means for capillary action to carry the liquid containing bluing and salt up from the main source of liquid. It also speeds evaporation and allows crystals to form across the entire garden.

Additions of bluing and salt on later days should be made by slipping the new liquid in below the rest of the growth. Capillary action will bring this new material up where the evaporation can cause additional formations of crystals.