How does electroplating work?

First, you have to choose the right electrodes and electrolyte by figuring out the chemical reaction or reactions you want to happen when the electric current is switched on. The metal atoms that plate your object come from out of the electrolyte, so if you want to copper plate something you need an electrolyte made from a solution of a copper salt, while for gold plating you need a gold-based electrolyte—and so on.

Next, you have to ensure the electrode you want to plate is completely clean. Otherwise, when metal atoms from the electrolyte are deposited onto it, they won't form a good bond and they may simply rub off again. Generally, cleaning is done by dipping the electrode into a strong acid or alkaline solution or by (briefly) connecting the electroplating circuit in reverse. If the electrode is really clean, atoms from the plating metal bond to it effectively by joining very strongly onto the outside edges of its crystalline structure.

Now we're ready for the main part of electroplating. We need two electrodes made from different conducting materials, an electrolyte, and an electricity supply. Generally, one of the electrodes is made from the metal we're trying to plate and the electrolyte is a solution of a salt of the same metal. So, for example, if we're copper plating some brass, we need a copper electrode, a brass electrode, and a solution of a copper-based compound such as copper sulfate solution. Metals such as gold and silver don't easily dissolve so have to be made into solutions using strong and dangerously unpleasant cyanide-based chemicals. The electrode that will be plated is generally made from a cheaper metal or a nonmetal coated with a conducting material such as graphite. Either way, it has to conduct electricity or no electric current will flow and no plating will occur.