There are a great many formulæ for the nickel as well as for the other baths, but the generally accepted one is composed of double nickel ammonium-sulphate, three parts; ammonium carbonate, three parts; and water, one hundred parts. Another good one is composed of nickel sulphate, nitrate, or chloride, one part; sodium bisulphate, one part; and water, twenty parts.
Nickel anodes are used in bath to maintain the strength, and great care must be taken to have the bath perfectly balanced—that is, not too acid nor too alkaline.
To test this, have some blue-and-red litmus paper. If the blue paper is dipped in an acid solution, it will turn red; and back to blue again if placed in an alkaline solution. If the nickel solution is too strong with alkali, a trifle more of the nickel salts must be added, so that both the red-and-blue litmus paper, when dipped in the liquid, will not change color. If the bath is too alkaline, it will give a disagreeable yellowish color to the deposit of metal on the kathode; and if too acid, the metal will not adhere properly to the kathode, and will strip, peel, or blister off.
Finishing
When the articles have been plated they will have a somewhat different appearance to what may have been expected. For instance, copper-plated articles will have a bright fleshy-pink hue; silver, an opaque creamy-white; gold, a dead lemon-yellow color, and nickel much the appearance of the silver, but slightly bluer in its tone. Articles removed from the bath should be shaken over the bath so as to remove the solution; then they should be immediately plunged into hot water, rinsed thoroughly, and allowed to dry slowly.
When a silvered or gilded object is perfectly dry it should be rubbed rapidly with a brush and some fine silver-polishing powder until the opaque white or yellow gives place to a silver or gold lustre. It will then be ready for burnishing with a steel burnisher, or the article may be left with a frosted silver or gold surface. Steel burnishers can be had at any tool-supply house, and when used they should be frequently dipped in castile soapy water to lubricate them. They will then glide smoothly over the surface of the deposited metal, driving the grain down and making it bright at the same time. If the soapy water were not used the action of the hard burnisher over the plate would have a tendency to tear away the film of deposited metal. The burnisher must always be clean and bright, otherwise it would scratch the plated articles; and, when not in use, keep the bright polishing surfaces wrapped in a piece of oiled flannel.
Small articles, such as sleeve-buttons, rings, studs, and other things not larger than a twenty-five-cent piece, may be polished by being tumbled in a sawdust bag. A cotton bag is made, three feet long and six inches in diameter, closed at one end and half-filled with fine sawdust. The articles are then put in the bag and the end closed. Grasp the ends of the bag with both hands, as if to jump rope with it; then swing it to and fro, until the articles have had a good tumbling. Look at them to see if they are bright enough; if not, keep up the tumbling.
When old work is to be re-plated, or gone over, it will be necessary to remove all of the old plate before a really good job can be done. In some cases it may be removed with a scratch-brush or pumice-stone; but, as a rule, it can be removed much quicker and more satisfactorily with acids.
Silver may be removed from copper, brass, or German-silver with a solution of sulphuric acid, with one ounce of nitrate of potash to each two quarts of acid. Stir the potash into the acid, then immerse the article. If the action becomes weak before the silver is all off, then heat the solution and add more of the potash (saltpetre). Gold may be removed from silver by heating the article to a cherry-red, and dropping it into diluted sulphuric acid—one part acid to two parts water. This will cause the gold to peel and fall off easily.