[Illustration:  Fig. 224.—­Glass-blowers from Twelfth Dynasty tomb.]

[Illustration:  Fig. 225.—­Parti-coloured glass vase, inscribed Thothmes III.]

[Illustration:  Fig. 226.—­Parti-coloured glass vase.]

[Illustration:  Fig. 227.—­Parti-coloured glass vase.]

[Illustration:  Fig. 228.—­Parti-coloured glass goblets of Nesikhonsu.]

Glass was known to the Egyptians from the remotest period, and glass-blowing is represented in tombs which date from some thousands of years before our era (fig. 224).  The craftsman, seated before the furnace, takes up a small quantity of the fused substance upon the end of his cane and blows it circumspectly, taking care to keep it in contact with the flame, so that it may not harden during the operation.  Chemical analysis shows the constituent parts of Egyptian glass to have been nearly identical with our own; but it contains, besides silex, lime, alumina, and soda, a relatively large proportion of extraneous substances, as copper, oxide of iron, and oxide of manganese, which they apparently knew not how to eliminate.  Hence Egyptian glass is scarcely ever colourless, but inclines to an uncertain shade of yellow or green.  Some ill-made pieces are so utterly decomposed that they flake away, or fall to iridescent dust, at the lightest touch.  Others have suffered little from time or damp, but are streaky and full of bubbles.  A few are, however, perfectly homogenous and limpid.  Colourless glass was not esteemed by the Egyptians as it is by ourselves; whether opaque or transparent, they preferred it coloured.  The dyes were obtained by mixing metallic oxides with the ordinary ingredients; that is to say, copper and cobalt for the blues, copperas for the greens, manganese for the violets and browns, iron for the yellows, and lead or tin for the whites.  One variety of red contains 30 per cent of bronze, and becomes coated with verdegris if exposed to damp.  All this chemistry was empirical, and acquired by instinct.  Finding the necessary elements at hand, or being supplied with them from a distance, they made use of them at hazard, and without being too certain of obtaining the effects they sought.  Many of their most harmonious combinations were due to accident, and they could not reproduce them at will.  The masses which they obtained by these unscientific means were nevertheless of very considerable dimensions.  The classic authors tell of stelae, sarcophagi, and columns made in one piece.  Ordinarily, however, glass was used only for small objects, and, above all, for counterfeiting precious stones.  However cheaply they may have been sold in the Egyptian market, these small objects were not accessible to all the world.  The glass-workers imitated the emerald, jasper, lapis lazuli, and carnelian to such perfection that even now we are sometimes embarrassed to distinguish the real stones from the false.  The glass was pressed into moulds made of stone or