How do you determine if a piece of heirloom jewelry has value? What do those barely discernible numbers inside a ring or on the back of a charm mean? The value of jewelry made from precious metals is determined by the purity of the gold, silver, or platinum it contains. The number found on jewelry is a karat hallmark and tells you how much of a metal is in that piece.
A hallmark is an indication of a piece of jewelry's precious metal content. The karat stamp has been used in European countries since the 14th century. The United States only adopted hallmarks in the early 1900s. European jewelry usually displays a three-number digit which marks the purity percentage of the metal, while U.S. jewelry opts for 18K, 14K, or 10K hallmarks. Today, very little jewelry is sold without a hallmark number on it.
Gold is measured against a 24-karat standard, with 24 karats being excellent. This means that something that is 24-karat gold is made up of 24 parts gold. All other gold marks are a percentage of 24 parts in this order: 22K (.917), 18K (.750), 14K (.585 or .583), and 10K (.417). Other gold purities and markings are used worldwide, but are not common in the United States.
The definitive marking for fine silver jewelry is "Sterling" which is .925 pure silver, mixed with minimal base metals. It is commonly marked "925". A "900" stamp on silver tells you that it is 9 parts pure silver and 1 part other metals.
Platinum is more rare and more expensive than gold. "Plat" or "950 Plat" is nearly pure platinum. "IridPlat" is 90 percent platinum mixed with 10 percent other metals.
If you want to know the purity of an unmarked piece of jewelry, a reputable jeweler can test it for a small fee. You can also purchase a precious metal testing kit; however, these are not always easy to use and understand unless you are adept at reading the results.
Even hallmarked jewelry can be faked. Unscrupulous dealers can simply purchase a stamp and mark inferior items with a realistic-looking hallmark. When in doubt, have the item tested.