The size used for filling the pores of plaster, wood, cloth, paper, etc., for the purpose of preparing it to receive paint or varnish, is usually made from glue. Where large quantities are used the size is obtained in barrels from the glue factory, and as the trouble and expense of concentrating it into cakes is thus avoided, it may be obtained at a very cheap rate. Size may be made by any one from clippings of skins, tendons, etc., boiled down to jelly and carefully freed from fat. Very fine size is prepared from parchment clippings. Where size is made from glue the following directions will prove useful:
Stretch the muslin well upon the frame. Soak over night one-half pound of the best white glue in 4 gallons water; in the morning turn it off and boil the glue. It must be very thin. Add a small piece of castile soap scraped fine. To have it more transparent add 2 oz. powdered alum. It must be put on quick, while warm. Gamboge for painting shades must be dissolved in alcohol; carmine in spirits of hartshorn.
Take 1 oz. of white glue, 1 oz. of white soap, and 1/2 oz. of alum. Soak the glue and the soap in water until they appear like jelly; then simmer in 1 quart of water until the whole is melted. Add the alum, simmer again and filter. To be applied hot.
This is an entirely different article, and is in reality a very strong drying oil colored to resemble gold, and used for cementing gold leaf to arcicles that are to be gilt.
To prepare it, drying or boiled oil is thickened with yellow ochre or calcined red ochre, and carefully reduced to the utmost smoothness by grinding. It is thinned with oil of turpentine. It improves by age.