Rhodium is a precious metal, a member of the platinum family. Rhodium electroplating is used on jewelry to provide a surface that will resist scratches and tarnish, and give a white, reflective appearance.
Rhodium plating is typically used on white gold. The term white gold is something of a misnomer. Gold is actually yellow, what jewelers call white gold today is an alloy (mixture) of gold and a white metal – usually nickel, silver, or palladium (another member of the platinum family). Metals known as white are actually more of a gray color, so white gold has a yellowish cast. The higher the karat weight, the more gold there is in the alloy, the more yellow the cast appears. Since the wearer of white gold is looking for a bright white look, a very thin layer of rhodium electroplating is used to make that jewelry shine.
It is important to know that rhodium plating does not last forever. The plating on something that takes a lot of wear, like a wedding ring, can wear away in as little as two years, while a necklace or pin that is worn less frequently or comes in less contact with your skin or the elements can keep its plating for many years. Often it is only when the rhodium plating starts to wear (the jewelry will have a yellowish cast) will you realize that the ring had been plated.
Though quality and durability are certainly a concern, the most troubling issue with the practice of rhodium plating is that it is incredibly toxic. When Rhodium solution wears out (and gets weak) it usually poured down the drain. The solution, containing sulfuric acid, is then flushed into the water system. Sulfuric acid is a known cancer causing agent.
It is also unsafe for workers to rhodium plate jewelry. The fumes of working with the chemical are toxic and usually used in an environment with poor ventiliation where workers are not properly outfitted with safety gear.
When purchasing white gold jewelry, be sure to ask if it has been rhodium plated.