Many people think that a stamp reading “925” on gold jewelry means that the piece contains 925/1000 gold, or in other words, it has 92.5% gold content.
However, 92.5% is not a standard gold purity value, and it does not correspond to any commonly used karat number. The closest level of purity to 92.5% is 22 karats, which translates to 91.7% purity.
If you see the number 925 stamped on gold jewelry, chances are that the mark does not refer to the gold content of the piece. 925 is a standard sign used to mark sterling silver, and the meaning of the stamp is that the silver content is 92.5% (i.e., the remaining 7.5% is comprised of other elements).
Why Stamp Gold Jewelry with a Silver Mark?
It seems puzzling why a gold piece would be marked with a stamp commonly used for silver. This is not so surprising, however, and most likely means that the jewelry is not made of solid gold but is actually a silver piece that has been gold plated. In this case, the 925 number makes sense, as it denotes the purity of the underlying silver core, not that of the gold plating.
So, if your gold piece is marked with a “925” stamp, what you have is likely gold vermeil (pronounced ver-may). This is the name used to denote silver jewelry covered with a thin layer of gold.
For a piece of jewelry to be sold as gold vermeil in the U.S., its gold plating needs to be at least 10 karats, or contain about 42% gold, and its thickness should be at least 2.5 microns.
How to Tell If Your Jewelry Is Really Gold Plated
If you want to make sure that the “925” mark on your jewelry means that it is gold plated instead of solid gold, the first thing to do is check for other stamps. Signs commonly stamped on gold-plated jewelry are GP, GEP, RGP, HGE, and HGP.
If there are no stamps indicating that the jewelry might be plated, then you can have the piece tested. Jewelers do such tests by applying acid to a very small piece of material taken from the jewelry. Acid tests are usually meant to establish the karat of a gold alloy, but they can also help find out if a piece is gold plated.
Determining the Purity of Gold Plating
Acid testing can reveal the gold content of the plating. Very often, gold-plated pieces are covered with 22-karat or 24-karat gold, which is rarely used to make solid-gold jewelry, as high-purity gold is too soft.
If there are any karat markings on the piece, they can also indicate the karat of the plating. For example, a mark that reads “22K” likely means that the top layer of the jewelry is 22-karat gold.
Gold karats are often expressed as parts per thousand in the form of three-digit numbers stamped on the jewelry.
Here are the most common karat markings (on the left) and their equivalents in parts per thousand (on the right):
24K – 999
22K – 917
20K – 833
18K – 750
14K – 583
10K – 417
(To convert purity numbers from parts per thousand to a percentage, simply divide by 10.)