The principal colors of gold for grinding are red, green, yellow. These should be kept in different amalgams. The part which is to remain of the first color is to be stopped off with a composition of chalk and glue; the variety required is produced by gilding the unstopped parts with the proper amalgam, according to the usual mode of gilding. Sometimes the amalgam is applied to the surface to be gilt, without any quicking, by spreading it with aquafortis; but this depends on the same principle as a previous quicking.
Writing on Metals.
To write on metals, take half a pound of nitric acid and one ounce muriatic acid. Mix and shake well together, and then it is ready for use. Cover the plate you wish to mark with melted beeswax; when cold, write your inscription plainly in the wax clear to the metal with a sharp instrument. Then apply the mixed acids with a feather, carefully filling each letter. Let it remain from one to ten hours, according to the appearance desired, throw on water, which stops the process, and remove the wax.
How to Transfer a Photographic Print to Glass.
To transfer a photographic print to glass for painting or for other purposes, separate the paper print from the background by steaming it; dry thoroughly, and having given the warmed glass an even coating of clean balsam or negative varnish, place the face of the print on the surface thus prepared, smooth it out and let it stand in a cool place until the varnish has hardened. Then apply water, and with a soft piece of gum-rubber rub off the paper so as to leave the photographic image on the varnished glass.
Stereotyping Woodcuts.
In stereotyping woodcuts, care should be taken that they are thoroughly dry before being sent to the foundry, as the intense heat to which they are subjected frequently causes them to warp and split, especially if pierced.
To Gild with Gold Leaf.
Bookbinders use gold leaf in two ways—to gild on the edge, and to place gold letters on the binding. To gild on the edge, the edge is smoothly cut, put in a strong press, scraped so as to make it solid, and the well-beaten white of an egg, or albumen, put on thinly; the gold leaf is then put on before the albumen is dry; it is pressed down with cotton, and when dry polished with an agate polisher. To put on the lettering, the place where the letters are to appear is coated with albumen, and after it is dry, the type to be used is heated to about the boiling point of water, the gold leaf is put on, either on the book or on the type, and then placed on the spot where the lettering is desired, when the gold leaf will adhere by the heat of the type, while the excess of gold leaf loosely around is rubbed off with a tuft of cotton.