For Gold Jewelry made in the United States or Canada it should be stamped 14K, 18K, 22K or some number greater then 9 and less then 24 with a "K" or "kt" after it. Since 10K is the minimum purity in the U.S. that an item can be sold as "Gold" and 24K is rarely used for making jewelry. The "K" stands for Karat. A Karat is a measure of gold purity. This is sometimes confused with Carat, which is a unit of weight used for diamonds and other gemstones that is equal to 200 milligrams.
1 Karat equals 1/24 of the whole. An alloy made of 14 parts pure gold and 10 parts of copper or some other metal is known as 14K or 14 Karat gold...18 parts pure gold and 6 parts of another metal, is 18K or 18 Karat Gold.
Outside of the U.S. and Canada, the spelling "Carat" is commonly used instead of "Karat" to describe gold purity. You will find the abbreviation "ct." being used and 14ct, 18ct or 9ct... as a purity stamp instead of 14K, 18K or 9K....( It is only in this context, that the words "Carat" and "Karat" describe the same thing, 1/24 part or 1/24 of the whole.)
In Europe, the Parts Per Thousand format is usually stamped to indicate an items gold purity, " .375 " for gold that is 37.5% pure, " .417 " for gold that is 41.7% pure (10K in the U.S.), " .585 " for gold that is 58.5% pure (14K or 58.3% in the U.S.) , " .750 " for gold that is 75% pure (18K in the U.S.).
For Sterling Silver it should be stamped " Sterling "," Ster ", ".925 " or have a symbol or mark that indicates that it is Sterling Silver and not silver plated or stainless steel. The standard or law for which an item can be sold as "sterling silver" is it must contain 92.5% pure silver. There are some resources on the internet to help you find sterling silver hallmarks from silversmith's all over the world.
For Silver, Platinum or Palladium Jewelry it is usually stamped .800, .950, .830, .900 or something in a .000 format. This format is simply expressing the items purity as Parts Per Thousand. If your item is genuine and marked .800 it is 80% pure. If it's marked .950 it's 95% pure. If it's marked .835 it's 83.5% pure precious metal. Platinum jewelry is usually stamped with a "Pt" or "Plat" after the purity.. ..ie, ".950 Pt" or ".950 Plat", "900 Pt" or "900 Plat".
Purity Stamps and Hallmarks:
Most all contemporary precious metal goods are by law, stamped to indicate their purity. If your item is unmarked, it may mean that it has been "electroplated" or that it may not be made from precious metal at all, so you will have to do a little more research. Possibly purchase a test kit or take it to a reputable jeweler for a purity test if you are unsure.
If the item is stamped "EPNS" or "EPBM" this indicates that it has been electroplated. When an item has been electroplated, it means that it only has a thin coating of precious metal instead of being a true alloy where the metals are mixed together at melting point temperatures. It is also worth noting that electroplated items are VERY common and basically worthless from a precious metal perspective. They do not contain enough gold or silver to merit refining.
The calculators are NOT intended to work with anything that has only been "Electroplated" with precious metal .