Rhodium is a very hard, chemically resistant, brilliant white precious metal which is often used as a plating on white gold, and other white metals, to give a tough, brilliant white, protective finish.
In practice the rhodium is electrochemically plated as a very thin layer. While it is not particularly difficult to plate a thin layer of rhodium onto a piece of jewellery using a quick dip and dunk this will not be enough to ensure that the metal is deposited firmly as a hard bright brilliant white coating.