The definition of porcelain tile is simply that it has less than .5 percent absorption. That makes these tiles very strong and dense. Because they are so dense they can be left unglazed and used on the floor. As they have no glaze to wear out they will stay the same color and appear the same for generations to come. One of the misconceptions that persists is the durability of glazed porcelain. When a porcelain tile is glazed it is the glazed surface that takes the wear, not the body. There are glazed porcelains (porcelain tiles) on the market that are only suitable for light duty or residential. Granted, this is not the norm, but they certainly are not unusual to find. On the other side of the spectrum we see double-charged porcelain tile where the effects we typically have only seen in glaze tile are being created by the addition of pigments to the second layer and then fused into rather than on the body; double charging is more for the infusion of stain resistance than it is to infuse a different color.