Fields Chromatography | Page 8

such subordination that neither of them
predominates to the eye, constitute the negative or neutral colours, of
which black and white have been stated to be the opposed extremes,
and greys their intermediates. Thus black and white are constituted of,
and comprise latently, the principles of all colours, and accompany
them in their depth and brilliancy as shade and light.
Semi-neutral Colours belong to a class of which brown, marrone, and
gray may be considered types. They are so called, because they
comprehend all the combinations of the primary, secondary, and
tertiary colours, with the neutral black. Of the various combinations of
black, those in which yellow, orange, or citrine predominates, have
obtained the name of brown, &c. A second class in which the

compounds of black are of a predominant red, purple, or russet hue,
comprises marrone, chocolate, &c. And a third class, in which the
combinations of black have a predominating hue of blue, green, or
olive, includes gray, slate, &c.
While treating of the classes of colours, it may not be out of place to
note here the difference between gray as spelt with an a, and grey as
spelt with an e, the two names being occasionally confounded. Gray is
semi-neutral, and denotes a class of cool cinereous colours, faint of hue;
whence we have blue grays, olive grays, green grays, purple grays, and
grays of all hues in which blue predominates; but no yellow or red
grays, the predominance of such hues carrying the compounds into the
classes of brown and marrone, of which gray is the natural opposite.
Grey is neutral, and is composed of or can be resolved into black and
white alone, from a mixture of which two colours it springs in an
infinite series.
It must be observed that each colour may comprehend an indefinite
series of shades between the extremes of light and dark, as each
compound colour also may comprise a similar series of hues between
the extremes of the colours composing it. And as the relations of
colours have been deduced regularly, from white or light to black or
shade; so the same may be done, inversely, from black to white. On this
plan the tertiaries, olive, russet, and citrine, take the place of the
primaries, blue, red, and yellow; while the secondaries still retain their
intermediate station and relation to both.
Thus, russet and olive compose or unite in dark purple; citrine and
olive in dark green; russet and citrine in dark orange. The tertiaries
have, therefore, the same order of relation to black that the primaries
have to white; and we have black primaries, secondaries, and tertiaries,
inversely, as we have white primaries, secondaries, and tertiaries,
directly. In other words, we have light and dark colours in all classes.
CHAPTER IV.
ON THE DURABILITY AND EVANESCENCE OF PIGMENTS.

Pigments may be defined as colours in a solid or insoluble state,
prepared for the artists' use. Hitherto, we have treated of colours in the
abstract sense, as appealing to the eye only: we have now to consider
them as material bodies.
As colour itself is relative, so is durability of colour relative. For the
reason that all material substances are changeable and in perpetual
action and reaction, no pigment is so permanent as that nothing will
alter its colour. On the other hand, none is so fugitive as not to last
under some favouring circumstances. Time, of long or short
continuance, has often the effect of fire, more or less intense. Indeed, it
is some sort of criterion of the stability and changes of colour in
pigments, that time and fire are apt to produce similar effects thereon.
Thus, if fire deepen, or cool, or warm a colour, so may time; if it vary
its hues, so may time; if it destroy a colour altogether, so may time
ultimately. The power of time, however, varies extremely with regard
to the period in which it produces those effects, that are instantly
accomplished by fire.
That there is no absolute but only relative durability of colour may be
proved from the most celebrated pigments. For instance, the colour of
native ultramarine, which will endure a hundred centuries under
ordinary circumstances, may be at once destroyed by a drop of lemon
juice; and the generally fugitive and changeable carmine of cochineal
will, when secluded from light and air, continue fifty years or more;
while fire or time, which merely deepen the former colour, will
completely dissipate the latter. Again, there have been works of art in
which the white of lead has retained its freshness for ages in a pure
atmosphere, but has been changed to blackness after a few days' or
even hours' exposure to foul air. These and other peculiarities of
colours will be noticed, when we come to speak