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.
Amber Varnish has been more reputed in painting than it merits. The process by which it is prepared is the same as that of copal; but amber is more difficult of solution, is of a deeper colour than copal, and, owing to the succinic acid it contains, dries very slowly in solution. Amber of the palest colour is most easily dissolved, and at the same time affords the best varnish; but, at present, it is rarely employed in painting.