Colophony is the non-volatile portion of the oleo-resinous exudation of various species of pine trees, which are to be found in enormous quantities in the producing regions. This oleoresinous exudation is known as crude turpentine, which, on steam distillation yields the oil of turpentine of commerce, leaving the rosin behind. Common resin, or colophony, is used for numerous purposes in the arts, including the manufacture of very low grade varnishes, cheap household soaps, for the distillation of rosin spirit and rosin oil, and for the manufacture of metallic resonates, which are added to varnishes to assist rapid drying. Varnish made from colophony is of very low grade and weathers very badly: indeed, powdered rosin can usually be scratched with the finger from the varnished article. A small, but very important technical use for colophony has quite recently arisen in the manufacture of ester gums, as they are called. The colophony, being almost entirely of an acid nature, combines with the alcohol glycerine, and with certain other bodies containing hydroxyl groups, forming a stable ester, or salt of the acid body present. These “ester gums” have been found to be far more useful than ordinary colophony for varnish manufacture, as the dried varnish weathers well, and cannot be scratched or removed with anything like the ease that colophony varnish can.