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Zinc-cobalt Blue








Cobalt, as furnishing a blue colour, is usually associated with alumina,
silica, or tin; and, as furnishing a green colour, with zinc. But there
is obtainable a compound of zinc and cobalt which gives a blue not only
free from green, but inclining rather to red. It is made by adding to a
solution of ordinary phosphate of soda in excess a solution first of
sulphate of zinc and then of sulphate of cobalt, and washing and
igniting the precipitate. The result is a vitreous blue with a purple
cast, of little body, and exceedingly difficult to grind. Altogether, it
is not unlike smalt, over which it has no advantages as an artistic
pigment either in colour or permanence. For tinting porcelain, however,
it is admirably adapted, imparting thereto a very pure dark blue of
extraordinary beauty. This blue is distinguished from smalt by
dissolving in acetic acid.

* * * * *

Compared with the wide range of yellows, or even with reds, the artist
finds the number of his blues limited. The perfect native and excellent
artificial ultramarines, the good blues of cobalt, the fair Prussian
blue, and the doubtful indigo, are the four varieties he has for years
been in the habit of using, and is still mainly dependent on. Our
division, therefore, into permanent, semi-stable, and fugitive, is
easily effected.

In the front rank, pre-eminent among blues as among pigments generally,
stands genuine ultramarine. Behind it, are the artificial ultramarines;
and behind them again, cobalt and cerulian blue. To a greater or less
extent, all these are durable.

Among the semi-stable, must be classed cyanine or Leitch's blue, smalt,
and Prussian blue.

To the fugitive, belong indigo and the somewhat more permanent intense
blue, Antwerp blue, and the copper blues.

In this list of blues, which grace or disgrace the palette of the
present day, there is one colour which, although not permanent, is
almost indispensable. As yet, the chemist cannot in all cases lay down
the law as to what pigments may or may not be employed. The painter who
unnecessarily uses fugitive colours must have little love for his
craft, and a poor opinion of the value of his work; but, even with the
best intentions and the utmost self-esteem, the artist cannot always
confine himself to strictly stable pigments. He has no right to use
orpiment instead of cadmium yellow, or red lead instead of vermilion, or
copper blue instead of cobalt: he has no business to employ indigo when
Prussian blue saddened by black will answer his purpose; but--what
pigment can he substitute for Prussian blue itself? None. In its
wondrous depth, richness, and transparency, it stands alone: there is no
yellow to compare with it, no red to equal it, no blue to rival it. In
force and power it is a colour among colours, and transparent beyond
them all. The great importance of transparent pigments is to unite with
solid or opaque colours of their own hues, giving tone and atmosphere
generally, together with beauty and life; to convert primary into
secondary, and secondary into tertiary colours, with brilliancy; to
deepen and enrich dark colours and shadows, and to impart force and tone
to black itself. For such effects, no pigment can vie with Prussian
blue. What purples it produces, what greens it gives, what a matchless
range of grays; what velvety glow it confers, how it softens the
harshness of colours, and how it subdues their glare. No; until the
advent of a perfect palette, the artist can scarcely part with his
Prussian blue; nor can the chemist, who has nothing better to offer,
hold him to blame. It is for Art to copy Nature with the best materials
she possesses: it is for Science to learn the secrets of Nature, and
turn them to the benefit of Art.






TTITLE SECONDARY ORANGE


Orange is the first of the secondary colours in relation to light, being





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