The MOS treatment in this commercial product description was discovered in Bordeaux, France and first used on a building in 1949. It is designed for use on calcareous material (limestone or sandstone), and consists of an aqueous solution of associated stable metallic salts, with varying formulations. Besides arresting growth of fungi, algae and lichens, the solutions are claimed to have bactericidal and anticryptogamic properties and block the action of frost to cause cracks (and protect from freezing to -20 to -22°C). They apparently do not harden the stone or change its structure or appearance (except to whiten with some products), are inexpensive and easy to apply by spray or brush, and safe to handle. For example, MOS-Calcaire-Monument converts bicarbonates back to insoluble carbonates in limestones. A complementary product, L.110, a solution saturated with lime, deposits calcite microcrystals on the surface. For sandstones, other combined salts are incorporated in the series of liquids. Products are available to remove growths such as mosses and lichen prior to impregnation of the stone.