Salt Crystal Garden

    Kids, in a glass or plastic bowl put 1-3 small pieces of porous materials such as coal, charcoal, brick, tile, cement and/or sponge. On day 1, pour two tablespoons each of water, table salt, and Mrs. Stewart's Bluing (MSB) solution (more on this later) directly over the porous materials. On day 2, sprinkle two more tablespoons of salt over them. On day 3, pour into the bottom of the bowl (not directly on the porous pieces) two tablespoons each of salt, water, and Mrs. Stewart's Bluing, and then add a few drops of food coloring or ink to each piece. By this time a beautiful flower-like growth should have appeared. It may be necessary to add two tablespoons of household ammonia to aid the growth. A free circulation of air is necessary, and these formations will develop better where the air is dry. To keep it growing add more MSB, salt, and water from time to time. It will "bloom" indefinitely into beautiful rosebuds of crystal. Take care to keep the majority of the porous pieces above the liquid level.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    How Does It Grow? Table salt (NaCl) can be dissolved in water. As salty water evaporates, some of the salt cannot be retained and crystals of salt form along the edges of a container (precipitation). This recipe calls for large amounts of salt with little liquid so that crystallization takes place quickly. MSB is a colloidal suspension of extremely small particles of blue iron powder (ferric hexacyanoferrate) in water. As the water evaporates, two things happen. The blue particles can no longer be supported and the excess salt cannot stay in solution. The salt crystallization process takes place around the blue particles (which act as "nuclei" or "seeds"). Small amounts of ammonia are added to speed up evaporation.

    The purpose of the porous material is to provide a means for capillary action to carry the liquid containing bluing and salt up from the main source of liquid. This further speeds up evaporation and causes the crystals to form over a larger area than just the rim of the bowl. Additions of bluing and salt on later days should be made by slipping the new liquid in below the rest of the growth. No chemical reaction takes place in this process, just dissolving and recrystallization. But it is fun and pretty, and involves common household chemicals. MSB is nontoxic, biodegradable, non-hazardous, and environmentally friendly.

    Color experts tell us that the brightest of whites has a slight blue hue. Simple bleaching is not enough to make new white clothes acceptable to customers, so manufacturers of sheets, towels, shirts, etc., "blue" them too. After fabric is used, the effects of the bleaches wear off and clothes begin to "yellow" after repeated washings. The fabric is clean but it is not "snow-white". To counteract the yellow, blue must be added. A little dilute MSB in the washing process adds the necessary tint; it does not remove stains or clean, but it optically whitens white fabric. 


    Kathleen Carrado Gregar, PhD, Argonne National Labs
    November 2002


    References: for more information and to order a Salt Crystal Garden Kit.