Why is white gold so often plated? White gold is an alloy, meaning gold mixed with other metals such as nickel or palladium, copper and zinc 1. White gold can look faintly yellow, so it is often plated with rhodium, which gives it a bright white colour 6. Rhodium itself is a hard, shiny, silvery metal that strongly resists corrosion (damage caused by chemical reactions) 4.
How is it done? Rhodium is applied by electroplating, a process that lays a very thin layer of metal onto the piece. One manufacturer’s rhodium solution, made for uses such as jewellery, gives a bright white finish at less than 0.5 micrometres (µm) thick 3.
Why does this matter once you own the ring? Rhodium plating wears away gradually, so white gold needs replating from time to time 1. Regular contact with water and the chemicals in some soaps and shampoos can dull the rhodium finish 6. As it wears, the white gold underneath shows through, and its colour may not match the rhodium well 2. If you are still choosing a metal, see White gold vs platinum.
Example: Imagine a white gold ring that looked bright white when it was new. After a while, parts of the band start to look slightly warmer in colour. That is the rhodium plating wearing thin and the white gold showing through. It is not a sign that the gold is fake, and a jeweller can replate the ring.