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Gambodium Gambogium &c Is The Produce Of Several Kinds Of Trees








The natives of the coast of Coromandel call the tree from which it is
principally obtained Gokathu, which grows also in Ceylon and Siam. From
the wounded leaves and young shoots the gamboge is collected in a liquid
state and dried. Our indigenous herb Celandine yields abundantly, in the
same manner, a beautiful yellow juice of the same properties as gamboge.
Gamboge is of a gum-resinous nature and clear yellow colour. It is
bright and transparent, but not of great depth, and in its deepest
touches shines too much and verges upon brown. When properly used, it is
more durable than generally reputed, both in water and oil; and
conduces, when mixed with other colours, to their stability and keeping
their place, on account of its gum and resin. It is deepened in some
degree by ammoniacal and impure air, and somewhat weakened, but not
easily discoloured, by the action of light. Time effects less change on
this colour than on other bright vegetal yellows; but white lead and
other metalline pigments injure, while terrene and alkaline substances
redden it. In water it works remarkably well, and forms an opaque
emulsion without grinding or preparation, by means of its natural gum;
but is with difficulty employed in oil, &c., in a dry condition. It
dries well, however, in its natural state, and lasts in glazing when
deprived of its gum. With regard to other colours it is perfectly
innocent, and though a strong medicine, is not dangerous or deleterious
in use. Gamboge has been employed as a yellow lake, precipitated upon an
aluminous base; but a better way of preparing it is to form a paste of
the colour in water, and mix it with lemon yellow, with which pigment
being diffused it goes readily into oil or varnish. Glazed over other
colours in water, its resin acts as a varnish which protects them; and
under other colours its gum acts as a preparation which admits
varnishing. It is injured by a less degree of heat than most pigments.

In landscape, gamboge affords with indigo or Antwerp blue clear bright
greens, and with sepia a very useful sober tint. For sunrise and sunset
clouds, a mixture of gamboge and cadmium yellow will be found useful.

TTITLE EXTRACT OF GAMBOGE

Is the colouring matter separated from its greenish gum and impurities
by solution in alcohol, filtration and precipitation, by which it
acquires a powdery texture, rendering it miscible in oil, &c., and
capable of being employed in glazing. At the same time it is improved in
colour, and retains its original property of working well in water with
gum. Gamboge is likewise soluble in caustic potash, forming a red
liquid, from which it is thrown down by acids.

TTITLE INDIAN YELLOW





Next: Is A Pigment Long Employed In India Under The Name Purree But Has Not

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