_Materials._--The prehistoric pottery of the earlier period is all of a soft body, faced with red haematite. As the pots were usually baked mouth downward, the brim was covered with the ashes; and these not being burnt through, reduced the red peroxide of iron to the black magnetic sesqui-oxide, such as is familiar to us in the black scale on sheet steel. The interior of the pots is likewise black, owing to the reducing gases from the ashes below; rarely the heat after the combustion has lasted long enough for the oxygen to pass through the pottery, and so redden the inside. Open dishes were also haematite-faced inside, and the iron is reduced to a brilliant mirror-like coat of black all over. The reason of the polish being smoother on the black than on the red parts is that carbonyl gas--which is the result of imperfect combustion--is a solvent of magnetic oxide of iron, and so dissolves and re-composes the surface facing. On once understanding the chemistry of this, it is needless to discuss the old idea that smoke blackened this pottery. Smoke--or fine carbon dust--could not possibly penetrate through close-grained pottery, and the black extends all through the mass, naturally owing to the action of reducing gases to which the pottery is quite pervious. There may perhaps be some other kinds of black pottery influenced by smoke; but it is far more probable that all black pottery is due to black oxide of iron produced by imperfect combustion, which is accompanied by smoke. In the later prehistoric age the pottery has a hard reddish buff body with white specks. In the pyramid period a smooth soft brown body is usual. Hard drab pottery also appears in the Vth and VIth dynasties. In the XIIth dynasty the common soft brown body is general, and extends to the XVIIIth. By the middle of the XVIIIth dynasty a hard drab ware with white specks and faced with a drab polish is very characteristic, and continues into the XIXth. Thence onward the brown body reasserts itself, with some inferior greenish drab ware about the XXIInd dynasty. Greek clays appear during the XXVIth, but probably all imported from Greece. Soft red pottery belongs to the Ptolemaic age. But the old soft brown rules in the Roman time, being at its worst in the early Coptic. The thin hard ware of the Constantine age is apparently not native, and may be due either to Nubian or Roman influence.