The manufacture of mineral and lake pigments : $b Containing directions for the manufacture of all artificial artists' and painters' colours, enamel colours, soot and metallic pigmentsBersch, Josef
Science
The manufacture of mineral and lake pigments : $b Containing directions for the manufacture of all artificial artists' and painters' colours, enamel colours, soot and metallic pigments
Bersch, Josef
Dyes and dyeing; Pigments
If manjit were a common article in the German market, it would be used
in the preparation of fine pigments with as much advantage as madder
and the various madder preparations.
=Chica Red, Curucuru, Carajuru.=—The colouring matter known under
these names rarely comes into commerce; it forms brownish-red masses
which acquire a peculiar golden glitter on rubbing. It is obtained
from the leaves of _Bignonia chica_, a native of tropical America. The
leaves are superficially dried and then covered with water; in the
warm climate the macerated leaves soon ferment, and a deep red powder
separates at the bottom of the vessel: this is the colouring matter; it
is dried, made into small cakes and brought into the market.
Chica red is only partially soluble in strong alcohol, the residue
chiefly consists of plant cells. Alum and stannous chloride precipitate
beautiful red lakes from the solution, which are distinguished by great
permanence when exposed to light. On account of the present high price,
this colouring matter has not yet obtained admission into the colour
industries, though it would be a valuable recruit.
Chica red has been little studied; an investigation would certainly
considerably increase our knowledge of the organic colouring matters.
Towards reducing agents it behaves in a similar manner to indigo; in
contact with caustic soda, grape sugar and water in closed flasks, a
violet liquid is produced; when exposed in an open vessel the violet at
once changes to brown, but if the liquid is syphoned off into dilute
hydrochloric acid a pure red precipitate separates, which is to be
regarded as the pure colouring matter.
CHAPTER LVII.
LICHEN COLOURING MATTERS.
Many lichens contain compounds from which colouring matters can be
obtained by appropriate treatment; the colouring matters known as
cudbear, archil and litmus were formerly much more extensively used in
dyeing than at present: like so many natural colouring matters they
have been replaced by coal-tar dyes.
The lichens which produce colouring matters live upon trees and rocks,
chiefly on the sea-shore; the colouring matters are thus generally
manufactured in places near the coast. The species principally used for
this purpose are _Lecanora_, _Rocella_ and _Usnea_.
The lichens contain colourless compounds, which by treatment with acid
or alkalis produce orcinol. In contact with moist air and ammonia,
orcinol is decomposed into water and orcein, which is the colouring
matter. The lichens are treated so as to produce the largest quantity
of orcinol, which is then converted into orcein. There is not space
here to enumerate and describe the many compounds obtained from
lichens, only the most important can be mentioned; these are erythric,
lecanoric and usnic acids. Lecanoric acid produces, under certain
conditions, orsellic acid, which is again changed to orcinol.
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