Zinc-cobalt Blue

: ON THE SECONDARY, ORANGE.

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