I keep seeing rings for sale on Etsy and Ebay that are advertised as "18k White Gold Plated Sterling Silver".
Does this really exist?
The short answer is NO.
Sterling Silver, a precious metal, is a white metal but it tarnishes fairly easily. The jewelry industry is always searching for better alloys to mix with fine silver to create a more tarnish-resistant metal. Regular fine silver is far less prone to tarnishing, but it's really too soft to safely hold a gemstone, so it's alloyed (mixed) with other metals. Copper is usually used in the ratio of 92.5% fine silver to 7.5% copper. That's why Sterling Silver is always marked ".925" to indicate the 92.5% pure fine silver (an industry standard). Some new alloys such as Argentium Sterling Silver are on the market and are very tarnish resistant (the alloy is Germanium, which is not reactive).
Often, sterling silver rings and other jewelry is plated with Rhodium. Rhodium is a very hard, bright white metal, a member of the Platinum family of metals. It is very corrosion resistant, and provides a shiny and bright finish to Sterling Silver, plus keeps the silver from scratching. And wherever silver is scratched, it is more apt to tarnish there.
Black Rhodium plated Sterling Silver is also very popular.
Sterling Silver jewelry is a great alternative to White Gold as far as appearance.
What about Sterling Silver plated with Yellow or Rose Gold?
Sterling silver jewelry is also sometimes plated with Yellow Gold and Rose Gold in various karats---14k, 18k and even 24k pure yellow gold. (And sometimes even "Green Gold".) When there is a heavy enough plating of yellow or rose gold, it is called "Vermeil". Only sterling silver that is plated with at least 2.5 microns of 14k gold (or higher) can be called, by law, Vermeil. Even Fine Silver (97% silver or more) is plated with gold to give it that solid gold look. It CANNOT---by law---be called "Vermeil" if it doesn't reach this standard of gold thickness over sterling or fine silver. There is ONLY Rose Gold Vermeil and Yellow Gold Vermeil (no "white gold").
But is Sterling or Fine Silver EVER plated with white gold?
Like Sterling Silver, even White Gold jewelry (especially rings) is almost always plated with Rhodium. That's because "white gold" is actually yellow gold that is alloyed with white metals to give it a whiter look. However, the resulting white gold still has a yellowish cast. A lot of people love the "pop" that Rhodium gives the white gold, and makes diamonds appear whiter. Even yellow gold jewelry is sometimes plated with Rhodium to give it a whole new look. Rhodium plated white gold also helps the gold resist scratching. Even Platinum jewelry is plated with Rhodium.
So why are sellers claiming their sterling silver is plated with 18k White Gold?
Well, it's just what I call "creative marketing". Others may call it "misinformation" which means "fraud". They think that consumers feel that "white gold" over Sterling Silver is more high-end sounding, I guess. Actually, Rhodium (like Platinum) is one of the most expensive metals.
So if you see a ring that is stamped "925" then it is Sterling Silver, and is likely plated with Rhodium. It is NOT plated with white gold. EVER.
Is there such a thing as White Gold Plated jewelry?
Yes. Inexpensive brass jewelry (which is not a precious metal) is given a "flash" plating with white gold. A lot of very inexpensive plated brass charms and chains and other jewelry items can be found all over Etsy and Ebay. These are often made in Korea and China.
And while we're on the subject of "plated"....
There is NO SUCH THING as "Sterling Silver Plated" jewelry!! For example, you might see something advertised as "Sterling Silver Plated Chain..." Sterling Silver is a term used ONLY for solid sterling silver items, and would be marked with "925". Jewelry, like chains and so forth, can be "silver plated" which is actually plated with a very small amount of fine silver---not "sterling". Sellers use that term so you THINK you're getting Sterling Silver, when you are not. Or perhaps they're trying to say their item is plated with ACTUAL silver, rather than a silver-colored metal or even paint. They would be far better off (and more honest) to call it "fine silver plated".