Abstract: A method of providing a safe, decorative coating for a porous decorative mass, such as a coral piece adapted to be used as an ornament in an aquarium. In the preferred embodiment, bleached coral, real or artificial, is coated with a solution prepared from acetone, toluene, polystyrene granules, and a non-water soluble dye. Besides coloring the coral, the coating seals the pores of the coral and prevents increases in the alkaline content of the aquarium water thereby rendering the water safe for tropical fish.