Glazed ceramic tiles are usually little less robust in terms of density and thickness than unglazed tiles. Glazed ceramic tiles are more resistant to staining due to the protective non-porous layer of liquid glass. Some varieties of glazed ceramic tile are fired at higher temperatures than others, and therefore are harder as well. This can often be determined by how light or dark the glaze is, the lighter glazes for ceramic tile generally being harder than the darker glazes. Mat and satin finishes are generally harder than shiny glazes, but more prone to staining.