Field's Chromatography: or Treatise on Colours and Pigments as Used by ArtistsField, George
Science
Field's Chromatography: or Treatise on Colours and Pigments as Used by Artists
Field, George
Color; Colors; Painting -- Technique
is a brilliant bluish purple of much richness, employed in draperies and
the like. It is prepared by precipitating an alcoholic extract of the
root of the _Anchusa tinctoria_, commonly known as alkanet, a plant
growing in the Levant, and some other warm countries. It was used by the
ancients as a dye, or as a groundwork to those stuffs which were to be
dyed purplish-red: the ladies in ancient times also employed it as a
paint. Its colouring matter or _anchusin_ has the character of a resin,
and is dark-red, softened by heat, insoluble in water, soluble in
alcohol and alkalis, and freely so in ether, fats, and volatile oils, to
all of which it imparts a brilliant red hue. To obtain anchusin, all the
soluble matters are first abstracted from the bruised root by water: it
is then digested in a solution of carbonate of potash, from which it may
be readily precipitated by an acid. Its alcoholic solution yields with
different reagents crimson, flesh-coloured, blue, and violet
precipitates, none of which, however, can be classed as durable. The
variety under notice, violet carmine, resembles the other colours
afforded by alkanet in not being able to withstand the action of light.
On continued exposure, it loses its beauty and brightness, together with
much of its colour, and, like Indian purple, assumes an inky blackness.
Hence it is unsuited to permanently pure effects, and should only be
used in body.
* * * * *
215. _Archil Purple._
Archil may be regarded as the English, cudbear as the Scotch, and litmus
as the Dutch name for one and the same substance, extracted from
several species of lichens by various processes. These lichens, which
are principally collected on rocks adjacent to the sea, are cleaned and
ground into a pulp with water, treated from time to time with ammoniacal
liquor, and exposed with frequent agitation to the action of the
atmosphere. Peculiar principles existing in the lichens are, by the
joint instrumentality of the air, water, and ammonia, so changed as to
generate colouring matter, which, when perfect, is expressed. Soluble in
water and alcohol, this colouring principle yields by precipitation with
chloride of calcium a compound known as 'Solid French Purple', a pigment
more stable than the archil colours generally, but all too fugitive for
the palette.
216. _Bismuth Purple._
A purple powder is capable of being produced from bismuth by passing
chlorine gas through the hydrated oxide suspended in a saturated
solution of potash. As soon as the oxide becomes brown-red, the mixture
is boiled and the liquid decanted off at once, the residue being
immediately washed first with alcohol and then with water. On the whole,
the result is not, for an artistic pigment, worth the trouble involved
in the preparation.
217. _Burnt Madder_
Public-domain text, read in full here on John Shaqi.
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