copper, and the blue with iron. The latter dark azure iron-blue was,
probably, the produce of the Alexandrian furnaces, at a very early period
of Glass-making: it was obtained from iron by the late Mr. James Green,
who, so far, confirmed Klaproth's analysis. The specimen of the Egyptian
idol, and the
by Mr. Banks, at Thebes
in Plate 2, are of this variety. Cobalt was probably not used for Glass
coloration till a much later period: the Portland Vase and the Naples
Vase (Plate No. 1) have, no doubt, crude cobalt for their colouring
base (of the dark rich blue); whether they are late Egyptian or Grecian
manufacture, it is difficult to decide.
The foregoing and the following analysis
of coloured Glasses are extracted from a work by Minutoli, published at
Berlin, in 1836, entitled "Uber die Anfertigung und die Nutzanwendung
der Farbigen Gläçer bei den Alten:"
|Oxide of Lead
|Oxide of Iron
|Oxide of Copper
This difference is conjectured to be potash or alumine. Flint Glass
manufacturers produce a beautiful red from a mixture of copper and iron,
and sometimes accidentally: for instance when the ordinary metal mixed
specially for light green medical bottles, is nearly worked out, it will
assume the complementary colour—viz., a ruby red; so that the same
bottle will be parti-coloured red and green.