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Citrine Brown








From boiling, hot, or cold solutions of bichromate of potash and
hyposulphite of soda in excess, we have obtained an agreeable
citrine-brown colour, varying in hue and tint according to the mode of
preparation and proportions of materials employed. It is a hydrated
oxide of chromium which, when washed and carefully dried, yields a soft
floury powder. Transparent, and affording clear, delicate pale washes,
the oxide has not been introduced as a pigment; partly owing to certain
physical objections, and partly to a tendency to greenness. This
tendency is peculiar to all the brown chrome oxides of whatever hue,
whether hydrated or anhydrous; and indeed distinguishes more or less
nearly all the compounds of chromium. Green, in fact, is the natural
colour of such compounds, the colour which they are constantly
struggling to attain; and hence it is that the green oxides of chromium,
being clothed in their native hue, are of such strict stability. The
inclination to green which the citrine under notice possesses, may be
seen by washing the precipitate with boiling water. It has been
supposed that hydrated brown oxide of chromium is not a distinct
compound of chromium and oxygen, but a feeble union of the green oxide
with chromic acid. If this be the case, the citrine cast of the brown
oxide is easily explained, as well as the gradual addition to its green
by the deoxidation of the chromic acid.

In mixed tints for autumn foliage and the like, the tendency to green of
this citrine brown would be comparatively unimportant; but whether the
oxide be adapted to the palette or not, we believe the colour might be
utilized. In dyeing, for instance, the solutions of bichromate of potash
and hyposulphite of soda would be worth a trial, the liquids of course
being kept separate, and the brown washed with cold water. Various
patterns could be printed with the bichromate on a ground previously
treated with hyposulphite.

* * * * *

Several other browns, and ochrous earths, partake of a citrine hue, such
as Cassel Earth, Bistre, &c. But in the confusion of names, infinity of
tones and tints, and variations of individual pigments, it is impossible
to arrive at an unexceptionable or universally satisfactory arrangement.
We have therefore followed a middle and general course in distributing
pigments under their proper heads.

Of the three citrines in common use, Mars brown and raw umber are
strictly stable; while brown pink, the purest original citrine the
palette possesses, is either semi-stable or fugitive, according to the
colouring substance used in its preparation.





TTITLE TERTIARY RUSSET


Russet, the second or middle tertiary colour, is, like citrine,
constituted ultimately of the three primaries, red, yellow, and blue;
but with this difference--instead of yellow as in citrine, the archeus
or predominating colour in russet is red, to which yellow and blue are




Next: Subordinates For Orange And Purple Being The Immediate Constituents

Previous: Cassia Fistula



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