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Gamboge

Synonyms: Gamboge, Gomme-Gutte, Gummigutt

This gum-resin is produced by several species of Garcinia. Siam gamboge comes from G. Hanburyi (Hook, f.); Ceylon gamboge from G. Morella (Desv.). There are other species from which the same product is obtained in various parts of India, as G. Cambogia (Desrouss.) and G. elliptica. The fine, deep-coloured gamboge, produced by the Burmese G. heterandra (Wall.), may prove to be superior to Siam gamboge, but it has not yet become an article of European trade. Gamboge is a mixture of a gum soluble in water, and a resin which is soluble in alcohol, chloroform, ether, etc. The pipe-gamboge of Siam, which is as pure as any variety met with in commerce, contains about 78 percent of resin and 18 of gum. The resin, which is the true colouring-matter, may be easily obtained pure by crushing pipe-gamboge into fine powder, mixing it with a little water, and then shaking up the mixture with ether; the ether dissolves the resin alone. From the ethereal solution the colouring-resin is recoverable by evaporation; but it is better to add a little drying-oil and some copal-varnish before driving off the ether by means of a very gentle heat.

The coloured, semi-fluid mass which then remains may be preserved in bottles or tubes for use as an oil-paint. The resin of gamboge has the properties of an acid, and forms yellow, orange, or brown compounds, with soda, lime, baryta, and other bases. Some of these compounds might prove useful as paints.

Gamboge was used by the early Flemish oil-painters. In the seventeenth century it was largely employed to give a golden hue to the embossed leathers for which Amsterdam was famous.

In water-colour painting gamboge is not trustworthy. It is unaffected by sulphur compounds, but is darkened by ammoniacal fumes, and slowly bleached by strong light. Some samples prove, however, far less fugitive than others. In two years' exposure to sunlight, one sample of cake-gamboge lost more than half its original intensity; while a sample of moist gamboge, bought at the same time from the same maker, retained nine-tenths.

The same sample of moist gamboge, after seven years, still showed seven degrees out of the original ten of intensity.

As an oil-colour, gamboge affords a rich, transparent, golden or amber hue; it has some claims to the consideration of artists. To secure its permanence, admixture with oil alone does not, however, suffice; a resin such as copal, or Strasburg turpentine, or wax, or paraffin, must be used also. Some of Sir Joshua Reynolds' trials of gamboge prove this, those with oil alone being a name only now; while those with resin, or wax, retain their original hue very fairly, though they were spread upon the canvas in 1772. It must, therefore, be remembered that reliance cannot be placed upon the permanence of the ordinary gamboge oil-paint as met with in commerce.

Gamboge, from its resinous nature, shows, when laid on thickly as a water-colour, a rather shining surface. It appears to have little or no chemical action on other pigments (with the exception, perhaps, of white lead), although, if it be mixed with anything which contains lime, or other alkaline compounds, it becomes brownish, and darkens. Gamboge forms beautifully clear and rich greens with Prussian blue or indigo, but its place in water-colour painting may be advantageously taken by aureolin, and even by Indian yellow. When mixed with baryta yellow or cadmium yellow, the permanency of gamboge is enhanced.


Last Update: 2011-01-23