White gold products are routinely electroplated with a very expensive metal called rhodium. Rhodium is a platinum group metal that is intrinsically white and lustrous. Gold alloys are not pure white because they contain a high percentage of yellow gold. Rhodium is what gives white gold it's bright white look.
Because plating deposits a very thin layer of metal over the alloy, it is possible for it to wear off and reveal areas of the yellowish metal beneath. How often a piece of jewelry will need to be replated to retain its bright white appearance is affected by several factors: Lifestyle, body chemistry, and exposure to certain chemicals in the environment.
Re-plating is not difficult or terribly expensive. It is a routine final step in servicing such as sizing, prong repair, or repolishing. Typically customers do not have a need for frequent replating.
One of the advantages of platinum is that it is intrinsically white and does not require plating. However, white gold alloys are harder than platinum and resist scratching and deformation better.
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