When a sufficiently heavy coating of the copper has been applied, remove the object and wash thoroughly in running or warm water to free it from any remaining copper fluid. If this is not done the surface, in drying, will turn a dull brown, and will have to be bitten off with the acid solution for cleansing copper.
The finer the copper deposit the better and smoother it will be; the grain will be smaller, and it will not present a rough surface, which is always difficult to plate over with silver or gold, unless a frosted effect is desired. Non-conducting objects are usually plated with copper first, and then replated with the metal desired for the final finish.
To make the surface conductive, finely powdered black-lead, or plumbago of the best kind, or finely pulverized gas-carbon is brushed over the surface. This must be thoroughly done; and if the deposit is slow about appearing at any spot it may be hastened by touching it with the end of an insulated wire attached to the main conductor. This, of course, will only answer for objects strong enough to stand the brushing treatment; it will not do for flowers, insects, and other delicate things, that are to be silver or gold plated. These should be given a film of silver by soaking in a solution of alcohol and nitrate of silver, made by shaking two parts of the chemical into one hundred parts of grain-alcohol, with the aid of heat and in a well-corked bottle. When dry, the object should be subjected to a bath of sulphuretted hydrogen gas under a hood. The sulphuretted hydrogen is made by bringing a bar of wrought-iron to a white-heat in the kitchen range or furnace fire, and touching it with a stick of sulphur. The iron will melt and drop like wax. These drops should be collected in a bottle. Now pour over them diluted sulphuric acid, one part acid to three parts water, and the gas will at once rise. It will be quickly recognized by its odor, which is similar to that of over-ripe eggs. It can be led off through a tube to the place where you wish to use it, and when through, the operation of gas-generation may be stopped by pouring off the liquid.
All objects prepared in this way should be given a preliminary coating of thin copper before they are plated with any other metal.
Silver-plating
Plating in silver is done in practically the same way as described for the coppering process. Thin strips or sheets of pure silver are used for the anodes, and the electrolyte is composed of nitrate of silver, cyanide of potassium, and water.
Dissolve three and one-half ounces of nitrate of silver in one gallon of water; or if more water is needed to fill the tank, add it in the proportion of three and one-half ounces of the nitrate to each gallon of water. Dissolve two ounces of cyanide of potassium in a quart of water, and slowly add this to the nitrate solution. A precipitate of cyanide of silver will be formed. Keep adding and stirring until no more precipitate is formed, but be careful not to get an excess of the cyanide in the solution.
Gather this precipitate, and wash it on filtering-paper by pouring water over it. The filter-paper should be rolled in a funnel shape thus permitting the water to run away and leaving the precipitate in the paper. This precipitate is to be dissolved in more cyanide solution, and added to the quantity in the tank. There should be about two ounces of the potassium cyanide per gallon over and above what was originally put in.
The silver anodes show the condition of the fluid. If the solution is in good order they will have a clear, creamy appearance, but will tarnish or turn pink if there is not sufficient free cyanide in the solution.
The proper strength of current is indicated by the appearance of the plated objects. A clear white surface shows that everything is all right, the solution in proper working order, and the proper current to do the work. Too much current will make the color of the kathodes yellow or gray, while too little current will act slowly and require a long time to deposit the silver.