How porous the finished tile is determines where and how it can be used. Also the price, since porous tile is less expensive than vitreous, or non-porous, tile. Ceramic tile that is not porous at all is called "impervious" and is the most expensive. This situation leads to trade-offs in price versus use. Porous tile should not be used outdoors or in wet installations such as bathroom floors, shower floors or shower or bathtub walls.
Most ceramic tile is glazed. That is, a layer of glass-file material is added to the top of the tile to give it a shiny appearance. The glaze may be made up of one or more layers. Each tile a new layer is added the tile must be fired again. Art file with painted patterns actually baked into the glaze are fired several times. Each firing also increased the price. Like anything else, if you want more or better you have to be prepared to pay for it.
Glazes, especially the fancy art glazes, may render the tile unsuitable for certain applications. For instance, you wouldn't want to use tile with a delicate arty glaze on a floor, or even a countertop. However, they are just fine for walls or a backsplash. Glazed tile can be used in flooring if the glaze is tough enough. The only way to be sure the glaze will be strong enough is to actually buy a tile and subject it to the scuffs and stress of actual use. Bang on it with shoes, sneakers with cleats and anything else the floor is likely to come in contact with.
