Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/437

Rh a pint of vinegar. The design of this composition, usually employed in gilding looking-glass and picture frames, is to obviate the greasiness of the wood, and prepare it the better to receive the coats which are to be laid on, and to preserve it from the ravages of worms. When used it is mixed with a sufficient portion of good glue, boiling hot. In applying it to the gilding of plaster or marble, the salt must be left out of its composition, as, in damp situations, this would produce a white saline efflorescence on the surface of the gold.

Varnishes for Engravings, Paints, and Maps. A piece of plate glass is heated, and while yet warm a little wax rubbed over it, water is then poured over the plate, the moistened picture laid thereon and pressed closely down by means of a piece of filtering paper. When dry the picture is removed, and will be found to possess a surface of great brilliancy, which is not injured by the process of mounting. Boil Chio turpentine till brittle, then powder and dissolve in oil of turpentine. Canada balsam and clear white resin of each 6 ounces, oil of turpentine 1 quart, dissolve. Digest gum sandarach 20 parts, gum mastic 8 parts, camphor 1 part, with alcohol 48 parts. The map or engraving must previously receive one or two coats of gelatine.

Waterproof Glue. Dissolve $1/2$ ounce each of gum sandarach and mastic in 8 fluid ounces of strong alcohol, to which add ½ ounce of turpentine. Put the dissolved gums into a double glue-pot, add by degrees a hot thick solution of glue to which isinglass has been added, stir the whole over the fire until all the ingredients are thoroughly incorporated. Next strain through a cloth while hot, and it is ready for use. It may now be returned to the glue-pot, and $1/2$ ounce of very finely powdered glass added to it. It should be used quite hot. Take of shellac 3 parts, india-rubber 1 part by weight. Dissolve each separately in ether free from alcohol. It is best to do this in stoppered bottles and without heating, as the ether readily evaporates.