If, as I have said, there is little evidence for the existence of glass in Egypt before the Eighteenth Dynasty, it is quite otherwise with regard to a very similar substance, identical almost in chemical composition—one whose history can be traced much further back. On beads of clear rock crystal, dating from the First Dynasty, and it would seem from an even earlier period in some cases, we find a coating of turquoise blue transparent glaze[8]—the very glaze, in fact, that has given a prevailing tint to the vast series of smaller objects of Egyptian art that we see in the cases of our museums. A similar colour, I may observe, continued in favour in Mohammedan times, and indeed gives a dominant note to Oriental art in contrast to the ochry tints of yellow, red, and brown prevalent in the West. The Egyptians soon learned to apply this blue glaze—essentially a silicate of soda and copper—to the surface of other natural stones, and above all to a fritty porous earthenware, the so-called Egyptian porcelain. Such an alkaline glaze, indeed, will only adhere to a porous base of this kind, with which it becomes united on firing, by a chemical reaction, or at least by the solution in it of some of the silicates of alumina and lime in the clay. This glaze differs essentially from those used on true porcelain—these last are almost of the same composition as the ground they cover—but, as in the case of the glazes on porcelain, so the materials of the Egyptian glazes were probably first incorporated together in a partially fused frit which was then ground and mixed with water to form a soup-like ‘slip,’ into which the object to be glazed was dipped. There have been brought from Egypt a few rare objects carved out of a blue frit (probably similar to that used in the preparation of glazes), for which a very early date has been claimed. But such a frit is no true glass.