Coeruleum Of Pliny Were A Blue Copper Earth However That May Be In
:
ON THE PRIMARY, BLUE.
these days both names signify cobalt compounds, coeruleum being a
stannate of cobalt, and cyanine a mixture of cobalt and Prussian blue.
Unlike the former, cyanine, being composed of two old colours, can lay
no claim to originality. In the fourth chapter it was observed, "it is
quite possible for the artist to multiply his pigments unnecessarily.
Colours are sometimes brought out under new names which have no claim to
e regarded as new colours, being, indeed, mere mixtures. Compound
pigments like these may most frequently be dispensed with, in favour of
hues and tints composed extemporaneously of original colours upon the
palette." Whether these remarks are applicable to cyanine or not is a
question for artists to decide: in our opinion, with so many semi-stable
original pigments, the introduction of semi-stable compounds is to be
deprecated. Cyanine is a rich, deep, transparent blue, but its richness
and depth, as well as to a great extent its transparency, depend upon
Prussian blue, which is not strictly stable. Hence the peculiar
properties of cyanine remain unchanged only so long as the Prussian blue
itself, the pigment losing its colour by degrees on exposure to air and
light, and gradually assuming the tint of the paler but more permanent
cobalt. A mixture, be it remembered, necessarily partakes of the
qualities of its constituents, and if one of these be fugitive, the
compound cannot preserve its original hue.
Within the last few years, a compound similar to cyanine has appeared,