Page 493 - Oriental Series Japan and China, Brinkly

MANUFACTURING PROCESSES

with a vitreous flux, the composition of which varies
with the nature of the colour it is desired to obtain.

That which is most generally employed is known as

fondant aux gris. It is used for greys, blacks, reds,
blues, and yellows, and its ingredients are six parts of
red lead, two of silicious sand, and of liquid borax.

The colours are obtained ordinarily by mixing three

parts of the flux, by weight, with one part of metallic

oxide, so that the composition may be generally

expressed as follows :

Silica 16.7
50.0
Oxides of lead
Borax 8.3
Colouring oxides
25.0

100.0

Sometimes the mixture of oxide and flux is melted

or ground before using ; sometimes, on the contrary,

the oxides are simply mixed with the flux. The

colour obtained is immediately employed without
any prefatory fusion or calcination. If the colour is
to be produced by a combination of the oxide with

the flux, as is the case when oxide of cobalt is em-

ployed, it is necessary to melt the oxide previously

with the flux, in order that the colours may have the

required tone. But if the colouring matter belongs
to the oxide itself, and if the latter has only to be
disseminated and not brought into a state of combi-
nation with the flux, it must not be melted before use.

The various colours produced by peroxide of iron
belong to this category. Were the peroxide of iron

melted with the flux, the colour would be perceptibly
altered, and the second fusion undergone during the

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