Gilding for cheap work may be effected by using a copper anode in the place of a gold one, and re-supplying the gold solution as it becomes exhausted, by the addition from time to time of concen trated solution of cyanide of gold ; in this way, not only is the gilding of a very rich colour, but a larger surface may be coated at a small cost.
In gilding and silvering silk, cotton, and the like, one process consists in arranging the fabric in a tight position, and then immersing in a solution of acetate of silver, to which is added ammonia until the solution becomes fluid. After one or two hours' immersion the thread is to be dried and submitted to a current of pure hydrogen gas. The threads are then metallized, and will conduct a current of electricity ; they are then to be gilded by the methods usually employed. Another process is to dip a piece of white silk in an aqueous solution of chloride of gold, and expose it to the action of sulphurous acid gas, which may be done by burning a little sulphur, and confining the vapour in a box ; in a few seconds, the whole piece will be covered with a coat of reduced gold.
A very weak solution of sulphate of copper, applied with u camel-hair brush, and the spot touched with a steel or iron rod, will deposit a film of copper on pewter solder. This will be found a very simple and useful assistant in cases where it is troublesome to obtain a gold or silver deposit upon certain parts of work which had been repaired with soft solder. Lead edges of candlesticks, cruet-frames, and the like, may be slightly coppered in this way, by making up a bath of weak sulphate of copper solution, dipping the part to be coated therein, and touching the places to be coppered with a clean iron rod. With the exception of the extreme point, the iron rod may be coated with varnish, or with u solution of red sealing-wax, in spirit of wine, to prevent the metal from reducing the copper from its solution except where required to do so.
Good nickel plating may be effected by making up the bath with pure crystals of double-sul phate of nickel and ammonia, 1 lb. of the crystals being allowed to each gallon of water. The anodes required for, say a 50-gal. bath, should be 10 in number, each being at least 12 in. long by 6 in. wide. They are suspended on each side of the bath by copper hooks to the positive conducting pole, which may be of brass tubing with an iron core. The battery required for a bath the capacity we have indicated will be 4 Bunsen cells, about 2 gal., or a small dynamo-machine may be used instead. To prepare the double salt of nickel and ammonia, nitrate of nickel is dissolved
in its own weight of ammonia, the whole diluted with 20 to 30 times its volume of liquid bisulphate of soda, marking about 24° Blume. Nickel solutions like those of gold and silver do not readily dissolve the anodes, and consequently, unless these expose a surface considerably exceeding that of the articles to be plated, the deposit will got only be irregular but of an indifferent colour. Again, owing to the solutions of this metal being comparatively poor conductors of electricity, anodes must be placed opposite each side of the article to be plated, or surround it where its form is circular.
Tho cleansing baths required are a potash bath, a weak cyanide bath for brass or copper work, and a weak hydrochloric acid bath for steel or iron work. Tho surfaces of the metal to be depo sited are cleaned in the ordinary way, and placed in the hot potash bath for a short time, rinsed, then dipped in either the cyanide or hydrochloric acid bath, again well rinsed, and put in the nickel vat ; it is necessary that the articles should be struck, that is, receive an immediate coating, directly after immersion, after which deposition should be allowed to progress more slowly. The bath should be filled with work upon this system ; after a while the power may be gradually augmented until the required deposit is obtained. Although cast-iron work may be nickelled direct, it is an advantage to give the work a preliminary coating of copper ; the ordinary cyanide of copper solu tion may be used for the purpose, but for the cast iron it is necessary to have the solution rich in metal, and the temperature raised to 130° F. The coppering bath is advantageous, ae it enables one to discover the effects of cleaning and pickling before depositing the nickel, a matter of consi derable importance ; and it will also be found useful to use it before plating Britannia metal and tinned iron goods. When the double chlorides of nickel and ammonia are used in preference to the double sulphates of nickel and nickel and ammonia, the solution may be weaker, since the former solution is a better conductor than the latter, and is more readily affected by electrical action ; a mixture of the double sulphates and double chlorides has also been tried with tolerable success. If the deposits are of a dull yellow colour, or a pearl-grey, either the solution is faulty or the current of too low tension to yield the proper deposit, which should be nearly ae white as silver.