A fine colourless varnish may be obtained, by dissolving eight ounces of gum-sandarach and two ounces of Venice turpentine in thirty-two ounces of alcohol by a gentle heat. Five ounces of shell-lac and one of turpentine, dis solved in thirty-two ounces of alcohol by a very gentle heat, give a harder varnish, but of a reddish oast. To these the solution of copal is undoubtedly able in many respects. This is effeeted by triturating an ounce of powder ofgurn which has been well dried by a gentle heat, with a drachm of camphor, and, while these are mixing together, adding by degrees.four ounces of the strongest al cohol, without any digestion. Between this and the gold varnish there is only this difference, that some substances that communicate a yellow tinge ate to be added to the latter.
Ofl-varnishes are commonly mixed Immediately with the eolours, but lac or lacquer-varnishes are laid on by themselves upon a burnished coloured ground when they are intended to be laid upon naked wood, a ground should be first given them of strong size, either alone, or with some earthy colour mixed up with it by levigation. The gold lacquer is simply rubbed over brass, tin, or
silver, to give them a gold colour. (See LACQUER.) The coloured resins or gums, such se, dragon's-blood, &c., are used to colour varnishes.
The consist in a solution of resin in oil of turpentine. The varnish being applied, the essential oil flies oig and leaves the resin. This is used only for paintings.
Before a resin is dissolved in a fixed oil, it is necessary to render the oil drying. For this purpose the oil Is boiled with metallic oxides, in which operation the mucilage of the oil combines with the metal, while the oil itself 'unites with the oxygen of the oxide. To accelerate the drying of this varnish, it is neeessary to add oil of turpentine. When resins are dissolved in alcohol, the varnish dries very speedily, and is subject to track ; but this fault is corrected by adding a email- qnantity of turpentine to the mixture, which renders it brighter, and less brittle when dry.