This section is from the book "Chromatography; Or, A Treatise On Colours And Pigments, And Of Their Powers In Painting", by George Field. Also available from Amazon: Chromatography, or A Treatise on Colours and Pigments, and of Their Powers in Painting.
XV. Ft. Gamboge; or, as it is variously written, Gumboge, Camboge, Gambouge, Cambo-gia, Cambadium, Cambogium, Gambadium, Gam-bogium, etc. is brought principally, it is said, from Cambaja in India, and is, we are told, 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: indeed our indigenous herb celandine yields abundantly, in the same manner, a beautiful yellow juice of the same properties as gamboge. Gamboge is a concrete vegetal substance, of a gum-resinous nature, and beautiful yellow colour, bright and transparent, but not of great depth. 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 durability, by means 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, and terrene and alkaline substances redden it. It works remarkably well in water, with which it forms an opaque solution, without grinding or preparation, by means of its natural gum; but is with difficulty used in oil, etc. in a dry state. In its natural state it however dries well, and lasts in glazing when deprived of its gum. It is perfectly innocent with regard to other colours, and, though it is a strong medicine, is not dangerous or deleterious in use. Sir Joshua Reynolds and Wilson are said to have employed it, and so also we know did the amiable President West: the first of these used it softened into a paste with water, and the latter in a dry state precipitated upon whitening. It has also been employed as a yellow lake prepared upon an aluminous base; but a much better way than either is to dissolve it into a paste 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 other pigments.
Extract Of Gamboge is the colouring matter of gamboge separated from its greenish gum and impurities by solution in alcohol and precipitation, by which means it acquires a powdery texture, rendering it miscible in oil, etc. and capable of use in glazing. It is at the same time improved in colour, and retains its original property of working well in water with gum.