A descaling agent or chemical descaler is a liquid chemical substance used to remove limescale from metal surfaces in contact with hot water, such as in  boilers, water heaters, and  kettles. Limescale is either white or brown in colour due to the presence of iron compounds. Glass surfaces may also exhibit scaling stains, as can many ceramic surfaces present in bathrooms and kitchen, and descaling agents can be used safely to remove those stains without affecting the substrate since both ceramics and glass are unreactive to most acids.