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





Furnishes The Blue Are Added To Brown Or Yellow Frit To Obtain A General Effect Of A Picture Fourthly There Is The Contrast Of Colour facebooktwittergoogle_plusredditpinterestlinkedinmail

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