The tanks or vats employed to hold the plating solutions are generally made of heavy wood, such as oak lined with either lead, asphalt, guttapercha, or Portland cement ; the lining is necessary, since it has been observed that the wood unprotected absorbs considerable quantities of the solution ; guttapercha lined vats will do very well for sulphate of copper solutions, but this lining will not do for cyanides, as these attack the percha vigorously. Tanks of iron or slate, enamelled, are coming into very general use, especially for gilding solutions, when of course they are of comparatively small size ; the iron tanks are particularly useful for gilding, since they admit of heat being applied from below, which is absolutely necessary to the operation. The pickling and dipping liquids are often kept in vats of similar construction, but enamelled stone ware pans, well made, serve every purpose, and indeed may be used for the solutions themselves with advantage.
After dipping and rinsing, the various pieces are fixed to a brass wire, or hooked upon brass or copper hooks. Small articles of jewellery are suspended to a stout copper wire. These hooks are better if made of pure copper than of brass, and it is still better to use glass hooks, which are cheap and are not corroded by the acids. Such hooks or supports can be made by bending glass rods by the heat of a charcoal fire, or of a gas burner, to the desired shape. Those objects which cannot be suspended or attached to hooks, are put into perforated ladles of porcelain or stoneware. It is less economical, but sometimes absolutely necessary, to use baskets of brass or copper wire cloth. Those who frequently have to cleanse very small articles will find it advantageous to employ a basket of platinum wire cloth, which, although expensive in the first cost, will be found cheaper in the end, as it is almost indestructible.
When it is desired to prevent deposition upon certain parts of goods to be plated, these parts must be "stopped off" by being coated with any ordinary varnish ; if for a hot solution, copal is the best for the purpose.
Quicking or coating with a film of mercury is often necessary to secure an adherent deposit ; for surfaces of copper and its alloys solutions of nitrate or cyanide of mercury are applied ; and for general use almost any mercurial salt dissolved in cyanide of potassium will be found effectual.
The substances used for taking moulds from objects to he copied by electrotype are beeswax, stearine, plaster of Paris, fusible metal, and guttapercha; indeed, any substance that will receive and retain an impression, and is not liable to be affected by the solution from which the metal is to be deposited, will serve the purpose. The articles to be copied are generally composed either of
plaster of Paris or metal. Suppose, in the first place, the article to be copied is of metal, and a mould is to be taken from it in wax or stearine. The latter is not found to answer well alone ; when used it should be mixed with wax, about half and half, Whether the beeswax have stearine in it or not, it is better to prepare it in the following manner :—Put common virgin wax into an earthenware pot over a slow fire ; and when melted, stir in a little whitening ; this mixture tends to prevent the mould from cracking in the cooling, and from floating in the solution ; the mixture should be remelted two or three times before using it for the first time.
The article to be copied should be brushed over with a little sweet oil ; after which the super fluous oil should be wiped off with a piece of cotton. If the article has a bright polished surface, very little oil is required ; but if the surface be matted or dead, it requires more care with the oil. A slip of cardboard or tin is now bound round the edge, and should rise about one-fourth of an inch higher than the highest part on the face ; this &lie, hold the article with its rim a little sloping, then pour the wax in the lowest portion, and gently bring it level, so that the melted wax may gradually flow over ; this will prevent the formation of air bubbles. Care must be taken not to pour the wax on too hot, as that is one great cause of failure in getting good moulds ; it should be poured on just as it is beginning to set in the dish. As soon as the composition poured on the metal is set, undo the rim ; for if it was allowed to remain on till the wax became perfectly cool, the wax would adhere to it, and being thus prevented from shrinking, which it always does a little, would be liable to crack; remove to a cool place, and in about an hour the two will separate easily. When they adhere, the cause is either that too little oil has been used, or that the wax was poured on too hot.
Rosin has been recommended as a mixture with Wax, mixtures of which, in various proportions, have been used with success; but when often used, decomposition or some change takes place, which makes the mixture granular and flexible, rendering it less useful for taking moulds.