Youngs Demonstrative Translation of Scientific Secrets | Page 4

weight either of copal or amber, and add as much oil of turpentine as will enable you to apply the compound or size thus formed as thin as possible to the parts of the glass intended to be gilt; the glass is to be placed in a stove till it is so warm as almost to burn the fingers when handled. At this temperature the size becomes adhesive, and a piece of leaf gold applied in the usual way will immediately stick. Sweep off the superfluous portions of the leaf, and when quite cold it may be burnished, taking care to interpose a piece of india paper between the gold and the burnisher. It sometimes happens when the varnish is not very good that by repeated washing the gold wears off; on this account the practice of burning it in is sometimes had recourse to; for this purpose some gold powder is ground with borax, and in this state applied to the clean surface of the glass by a camel hair pencil; when quite dry the glass is put into a stove, heated to about the temperature of an annealing oven, the gum burns off; and the borax, by vitrifying, cements the gold with great firmness to the glass, after which it may be burnished.
The gilding upon porcelain is in like manner fixed by heat and the use of borax, and this kind of ware, being neither transparent nor liable to soften, and thus to be injured in its form in a low red heat, is free from the risk and injury which the finer and more fusible kinds of glass are apt to sustain from such treatment. Porcelain and other wares may be platinized, silvered, tinned, or bronzed, in a similar manner.
16. GILDING THE EDGES OF PAPER
The edges of the leaves of books and letter paper are gilded whilst in a horizontal position in the bookbinder's press or some arrangement of the same nature, by first applying a composition formed of four parts of Armenian-bole and one of candied sugar, ground together with water to a proper consistence, and laid on by a brush with the white of an egg. This coating, when nearly dry is smoothed by the burnisher, it is then slightly moistened by a sponge dipped in clean water and squeezed in the hand; the gold leaf is now taken up on a piece of cotton from the leathern cushion and applied on the moistened surface; when dry it is to be burnished by rubbing the burnisher over it repeatedly from end to end, taking care not to wound the surface by the point.
17. PROFESSOR WORTS' AMALGAM FOR SILVERING
This is the only means yet discovered for silvering iron directly, yet it is not so lasting as some of the other processes. Take quicksilver and the metal potassium, equal parts by volume, put them together in a tumbler, and if both metals be good there will be a brisk ebullition, which continues until an amalgam of the two is formed, then add as much quicksilver as there is of the amalgam; let it work till thoroughly mixed, and it is ready for use. This amalgam you may apply with a cloth to any metal, even iron, though it be a rusty bar, and you have it neatly silvered over.
18. FOR COPPERING IRON
This is the latest method, and that now in use. To a solution of sulphate of copper, add a solution of ferrocyanide of pottasium, so long as a precipitate continues to be formed. This is allowed to settle, and the clear liquor being decanted the vessel is filled with water, and when the precipitate settles the liquor is again decanted, and continue to repeat these washings until the sulphate of potash is washed quite out; this is known by adding a little chloride of barium to a small quantity of the washings, and when there is no white precipitate formed by the test, the precipitate is sufficiently washed. A solution of cyanide of potassium is now added to this precipitate until it is dissolved, during which process the solution becomes warm by the chemical re-action which takes place. The solution is filtered, and allowed to repose all night. If the solution of cyanide of potassium that is used is strong, the greater portion of the ferrocyanide of potassium crystalises in the solution, and may be collected and preserved for use again. If the solution of cyanide of potassium used to dissolve the precipitate is dilute, it will be necessary to condense the liquor by evaporation to obtain the yellow prussiate in crystals. The remaining solution is the coppering solution; should it not be convenient to separate the yellow prussiate by crystallization, the presence of that salt in the solution does not deteriorate it nor interfere with