How can electricity add a thin metal coating to another object?

A metal coating can be built from dissolved metal ions. In copper electroplating, an object is connected to the negative side of a suitable power supply while it contacts a solution containing copper ions.

At the object’s surface, copper ions gain electrons supplied through the electrical connection. They become neutral copper atoms that join a growing solid deposit. The coating is therefore newly formed metal rather than copper-colored liquid that has dried.

At the other electrode, a complementary reaction releases electrons into the circuit. With a copper source electrode, copper atoms can enter the solution as ions. Ionic motion through the liquid and electron transfer through the wires complete different parts of the process.

The deposited layer can change appearance or surface properties without replacing the whole object. Its quality depends on the original surface and controlled conditions. A coating that is uneven or poorly attached will behave differently from a carefully prepared continuous layer.