[W. Canning & Co.
Fig. 36.—General Arrangement of an Electroplating Shop.
When thoroughly cleaned the articles are ready to be placed in the plating vats. These vats are usually made of wood lined with chemically pure lead, or of iron lined with enamel or cement. Anode and cathode rods made of brass are placed across the vats, and from these the anodes of the various metals and the articles to be plated are hung by hooks of nickel or brass. Any number of rods may be used, according to the size of the vat, so long as the articles have an anode on each side. If three rods are used the articles are hung from the centre one, and the anodes from the outside ones. If a number of small articles are to be plated together they are often suspended in perforated metal trays. Small articles are also plated by placing them in a perforated barrel of wood, or wood and celluloid, which revolves in the solution. While the articles are being plated the revolving of the barrel makes them rub one against the other, so that they are brightly burnished. Dog chains, cycle chain links, button-hooks, and harness fittings are amongst the articles plated by means of the revolving barrel.
The strength of current required for different kinds of plating varies considerably, and if the work is to be of the best quality it is very important that the current should be exactly right for the particular process in hand. In order to adjust it accurately variable resistances of German silver wire are provided for each vat, the current having to pass through the resistance before reaching the solution. The volume and the pressure of the current are measured by amperemeters and voltmeters attached to the resistance boards. If the intensity of the current is too great the articles are liable to be “burnt,” when the deposit is dark coloured and often useless.
When exceptionally irregular surfaces have to be plated it is sometimes necessary to employ an anode of special shape, in order to keep as uniform a distance as possible between the electrodes. If this is not done, those parts of the surface nearest the anode get more than their share of the current, and so they receive a thicker deposit than the parts farther away.
An interesting process is that known as “parcel-plating,” by which decorative coatings of different coloured metals can be deposited on one article. For instance, if it is desired to have gold flowers on a silver brooch, the parts which are not to be gilded are painted over with a non-conducting varnish. When this varnish is quite dry the brooch is placed in the gilding vat and the current sent through in the usual way. The gold is then deposited only on the parts unprotected by varnish, and after the gilding the varnish is easily removed by softening it in turpentine and brushing with a bristle brush. More elaborate combinations of different coloured metals can be made in the same way.
Sugar basins, cream jugs, ornamental bowls, cigarette cases, and other articles are often gilded only on the inside. The article is filled with gold solution and connected to the cathode rod. A piece of gold wrapped in calico is attached to the anode rod, suspended in the solution inside the article, and moved about quickly until the deposit is of the required thickness.
The time occupied in plating is greatly shortened by stirring or agitating the solutions. This sets up a good circulation of the liquid, and a continual supply of fresh solution is brought to the cathode. At the same time the resistance to the current is decreased, and more current may be used without fear of burning. [Fig. 37] shows an arrangement for this purpose. The solution is agitated by compressed air, and at the same time the cathode rods are moved backwards and forwards. Plating solutions are also frequently heated in order to hasten the rate of deposition.
When the plating process is complete, the articles are removed from the vat, thoroughly swilled in water, and dried. They are then ready for finishing by polishing and burnishing, or they may be given a sort of frosted surface. During the finishing processes the appearance of the articles changes considerably, the rather dead-looking surface produced by the plating giving place to the bright lustre of the particular metal.
