Figure 1--> shows a typical plating tank containing copper sulfate (CuSO₄) solution. A dynamo supplies electric current, which is controlled by a rheostat. When the switch is closed, the cathode bar, which holds the work to be plated, is charged negatively. Some of the electrons from the cathode bar transfer to the positively charged copper ions (Cu²⁺), setting them free as atoms of copper metal. These copper atoms take their place on the cathode surface, copperplating it. Concurrently, as shown in the drawing, the same number of sulfate ions (SO₄^2-) are discharged on the copper anodes, thereby completing the electrical circuit. In so doing, they form a new quantity of copper sulfate that dissolves in the solution and restores it to its original composition. This procedure is typical of nearly all ordinary electroplating processes; the current deposits a given amount of metal on the cathode and the anode dissolves to the same extent, maintaining the solution more or less uniformly. If this balance is perfect and there are no side reactions or losses, a 100 percent cathode efficiency and 100 percent anode efficiency could possibly be realized.

Electroplating has become a large and growing industry with sophisticated engineering and equipment requirements. The metals that can be readily plated from aqueous solutions at high-current efficiencies near 100 percent can best be surveyed from Figure 2-->. It shows these metals in a single rectangle in their proper relationship to each other. The only metal shown outside the rectangle that is in common use is chromium, which is usually plated at low-current efficiencies of about 10–20 percent. Iron, cobalt, nickel, copper, zinc, ruthenium, rhodium, palladium, silver, cadmium, tin, iridium, platinum, gold, and lead are more or less commonly used for plating. The others can be deposited easily but have not found much use in this way either owing to cost or availability or lack of useful properties.