The construction of a ceramic tile is quite simple. The bisque is the body of the tile, made of clay. The glaze is colored glass, which provides the design and surface finish of the tile. These two components become permanently fused together in the firing process. Looking at the back of a tile, you’ll see that some tiles have darker bisque than others. These are “red body” tiles as opposed to those with a “white body.” They are simply different kinds of clay chosen to produce a certain visual effect; there is no difference in performance.