The term ceramics is derived from the Greek keramos – ‘ potter ’ s clay ’ . Gradually, this term has been extended to include all products made from ﬁ red clay, such as bricks, tiles, ﬁ reclay refractories, wash-hand basins and other sanitary ware, electrical porcelains and ornaments, as well as pottery tableware. Many substances now classed as ceramics in fact contain no clay though most are relatively, hard, brittle materials of mineral origin with high fusion temperatures. Thus, hydraulic cement is usually classed as a ceramic material, whilst a number of metallic oxides such as alumina, magnesia, zirconia and beryllia form the basis of high-temperature ceramic refractories. Some of the latter, in particular alumina and zirconia, along with recently developed materials like silicon nitride and the ‘ sialons ’ , boron nitride and boron carbide, have more sophisticated uses.