'Ceramic' comes from the Greek keramos, meaning pottery. Ceramics are made of clay. When fired in a kiln clay become extremely durable.Ceramics can be glazed with a glass which melts onto a clay. The chemical name for glass is Silicon dioxide - a primary constituent of sand. It is likely that process of glazing was discocvered when fires were made in the presence of clay and sand. A flux mixed with the glaze lowers its melting point. Lead oxide and Lead carbonate are common low temperature fluxes. The tile glaze can also be coloured, as was common practice in Ancient Mesopotamia. Ceramics are still hand painted but they can also be machine printed. The Arabs developed the art making coloured tiles and took it to Spain and Portugal. Glazed ceramics are cooler to touch than when unglazed, because the smooth surface conducts heat.