Many tiles, such as ceramic and some porcelain tiles, have a glazed surface. The glaze is a layer of glass that protects the tile base or “biscuit” and can make it more or less slip resistant depending on the finish of the tile. Bathroom tiles for instance are not recommended outside because they usually are a lot smoother and therefore don’t have great anti-slip properties. At the same time, an anti-slip exterior tile laid on a bathroom floor will make cleaning harder because of the coarse anti-slip finish. The glaze is added to the tile biscuit by firing in a kiln at temperatures greater than 1000 degrees Celsius. Glaze is available in glossy, matt, and textured finishes.