enamel

During glazing, transparent or coloured glass dust or glass powder is melted onto the surface of another material. This method is usually used for objects made of clay or loam, typically stoneware, porcelain, mosaic or bricks. This process seals the surface of such objects, making them impermeable to water and thus more durable. Glazes, however, also have an aesthetic effect: they make the otherwise dull objects lustrous.