Silver
Most silver sold for jewelry and utensils today comes in sterling form. Since pure silver is too soft for everyday use, 7.5% copper content is added for strength, leaving 92.5% silver. The sterling alloy was once the standard of Great Britain, meaning that 1 Pound "Sterling" had the exact value of 1 troy pound, or 12 troy ounces. Pure silver is currently close to 20 British Pounds per troy ounce, so you do the math! Common sterling hallmarks are "925", "STERLING", "STER", "STSI", and "STRLNG". They may be accompanied by a company's logo and/or country. Other alloys are used, mainly for coins and bullion. Common markings for these are 999 (pure silver), 900, 850, 800, 720, and 500 - though others exist. These are all based on parts per 1000. Perfect 1000 is not economically or scientifically feasible, so silver will generally not pass 999/1000. Most everything without these markings will be a material called nickel-silver, which contains no silver at all. Other names include "Brazil Silver", "German Silver", "Mexican Silver", or "alpacca".
© TIFFANY & CO. 925
Gold
Gold has two common hallmark systems. The karat system rates gold in parts per 24, where 14k is 14/24 purity. The other hallmark system is the same as silver with parts per 1000. Common karat to numeric values are 375/9kt, 585/14kt, 740/18kt, 916/22kt, and 999/24kt. Anything below 375/9kt is considered "junk gold" and holds little jewelry value. "GOLD", "AU", or equivalent names (i.e. "ORO" ) may accompany the hallmark, along with the company's logo. Depending on the color of gold, it will be allowed differently:
* Green Gold: silver
* Grey Gold: silver, manganese, copper
* Rose Gold: copper, silver
* White Gold: nickel, manganese, palladium
* Yellow Gold: brass
Other gold colors exist, but they are generally too brittle for jewelry, aside from manufactured gemstones.
Bullion will carry a 999 hallmark, and coins can have varying hallmarks from 500 through 999.
AU 10K
Platinum
Where gold and silver are extremely soft with high purity, platinum is a very firm metal. Thus, jewelry will be 90% or 95% pure with the balance made from other platinum group metals, like iridium. In this case, the content of both metals may be provided. Platinum grades can be hallmarked as percentage or parts per 1000. Due to the generally higher value of platinum than other common precious metals, the extra economic effort of going beyond the 99.9% purity in coins is common. (The American Platinum Eagles contain 99.95% platinum.)
10% IRID, PLAT
Other
Most other precious metals are graded as percentage or parts per 1000 and have either their chemical symbols (i.e. Ir, Os, Pd, Rh, Ru) or some abbreviation of their names in the language of origin.
Plated costume jewelry, despite even multiple layers of plating, has little precious metal value since a single vial of metallic solution can plate 1000s of jewelry items before depletion. A thicker type of plating, called "gold-filled" may be marked something like 14/20GF, meaning 1/20 of the jewelry content is 14kt gold - still little precious metal value since that would be under 1kt purity.
