Crystal garden grown using water glass
Image credit: S. Horbury.
Water glass is an aqueous solution of sodium silicate (Na2SiO3) – a concentrated, syrupy alkaline – made by fusing sodium carbonate with silica. It is used to preserve eggs, as a cement, in ore flotation, and for water- and fire-proofing.
Water glass can also be used to grow "crystal gardens." Crystals of various colored metal salts, such as copper sulfate, iron sulfate, and iron chloride are added to a jar containing a 50% solution of water glass. The corresponding metal silicates are formed as structures that resemble alien plants.