For centuries, the only precious white metal available was silver or base metal alloys (mixtures of metals) that were gray in hue.
Silver, an element in the periodic table known as Ag, has been utilized in jewelry through history from ancient times to today. It was favored for diamonds to accentuate their highlights and color.
Platinum (Pt) was known in the 1800's as an element but virtually never used in jewelry until around 1900. While some rare accounts of its use persist, examples are basically non-existent.
But in the early 1900s, a new metal alloy was developed. It was a mixture of yellow gold, with several possible other materials, and could include nickel, zinc, palladium, or silver.
In the US, white gold was patented by the Belais Brothers and introduced in 1917. That began a revolution in jewelry, and its use became widespread.
However, with all the formulas, the majority of the mixture is yellow gold. This results in a metal that has a subtle yellow cast or hue. To compensate, another precious metal, rhodium, is used to coat or plate the yellow gold.
Rhodium (Rh) is another metal element on the periodic table that is white, highly reflective, and bright. It can also be combined with platinum to make it harder.
If you see a piece of jewelry that is white gold, you can almost be sure it is covered or plated in rhodium. And yes, over time and with long use, it can wear away or fade. This is why some antique and vintage white gold jewelry appears dull or golden in cast. But this takes a long time.
White gold jewelry can be replated to bring back its sheen and presence. Most white gold comes in various standards from 10k, 14k, or 18k. Any of these hallmarks may be present on a piece of white gold jewelry. It is not uncommon to have no marks, however, and testing with acid or electronic devices determines the gold fineness or karat.