small weights for testing gold
and silver coins of later caliphs from A.D. 952 to 1171. The system was
not, however, Arab, as there are a few Roman vase-stamps and weights. Of
other medieval glass may be noted the splendid glass vases for lamps,
with Arab inscriptions fused in colours on the outsides. No enamelling
was ever done by Egyptians, and the few rare examples are all of Roman
age due to foreign work.

The manufacture of glass is shown by examples in the XVIIIth Dynasty.
The blue or green colour was made by fritting together silica, lime,
alkaline carbonate and copper carbonate; the latter varied from 3% in
delicate blues to 20% in deep purple blues. The silica was needed quite
pure from iron, in order to get the rich blues, and was obtained from
calcined quartz pebbles; ordinary sand will only make a green frit.
These materials were heated in pans in the furnace so as to combine in a
pasty, half-fused condition. The coloured frit thus formed was used as
paint in a wet state, and also used to dissolve in glass or to fuse over
a surface in glazing. The brown tints often seen in glazed objects are
almost always the result of the decomposition of green glazes containing
iron. The blue glazes, on the other hand, fade into white. The essential
colouring materials are, for blue, copper; green, copper and iron;
purple, cobalt; red, haematite; white, tin. An entirely clear colourless
glass was made in the XVIIIth Dynasty, but coloured glass was mainly
used. After fusing a panful of coloured glass, it was sampled by taking
pinches out with tongs; when perfectly combined it was left to cool in
the pan, as with modern optical glass. When cold the pan was chipped
away, and the cake of glass broken up into convenient pieces, free of
sediment and of scum. A broken lump would then be heated to softness in
the furnace; rolled out under a bar of metal, held diagonally across the
roll; and when reduced to a rod of a quarter of an inch thick, it was
heated and pulled out into even rods about an eighth of an inch thick.
These were used to wind round glass vases, to form lips, handles, &c.;
and to twist together for spiral patterns. Glass tube was similarly
drawn out. Beads were made by winding thin threads of glass on copper
wires, and the greater contraction of the copper freed the bead when
cold. The coiling of beads can always be detected by (1) the little
tails left at the ends, (2) the streaks, (3) the bubbles, seen with a
ma