The millesimal fineness system is used to show the purity of silver, gold, and platinum alloys by parts per thousand of pure metal by mass in the alloy. For example, if an alloy contains 92.5% silver, it is referred to as “925.” [NOTE: An alloy is a mixture of two or more metals to obtain desirable qualities such as hardness, lightness, and strength.]
Fine silver (99.9% pure) is too soft to use in jewelry or almost anything else because it bends, breaks, and stretches too much. For this reason, manufacturing jewelers and silversmiths mix copper with it to give it some strength without discoloring it. Copper is the industry standard. However, some countries use other alloys as well.
When you see “.999 fine silver” or “999” stamped on an item, it is considered pure silver. It is softer and more malleable than sterling silver. It is used in bullion bars, and is also known as three nines fine.
Sterling silver (also known as standard silver) is what jewelry and silverware are traditionally made from, which is 92.5% silver and 7.5% copper. That is why you sometimes see .925 stamped on your jewelry. In the U.S., only a minimum of 92.5% fine silver can be marketed as “silver.”
Sterling silver jewelry is often plated with a thin coat of .999 fine silver to give the item a shiny finish (called “flashing”). Silver will tarnish unless an anti-tarnish coat is added. Rhodium is sometimes used for this thin coat because it is very shiny and never tarnishes. However, rhodium is a very expensive option compared to the silver finish.
Coin silver is an alloy of 90% silver and 10% copper. Therefore its millesimal fineness is 900, also known as one nine fine. Most United States silver coins are made of coin silver.
Junk silver is an informal term used in the United States, United Kingdom, Canada, and Australia for any silver coin which is in fair condition and has no numismatic or collectible value above the bullion value of the silver it contains. Such coins are popular among people seeking to invest in silver, particularly in small amounts. The word “junk” refers only to the value of the coins as collectibles and not to the actual condition of the coins. Also, junk silver isn’t necessarily scrap silver.
A silver-plated item has a thin coating of silver deposited onto a base metal which has a lower value than silver. Once used as plating, silver cannot be easily recovered, so it is of no value to those who are accumulating silver as an investment. EPNS means electroplated nickel-silver and is sometimes stamped on silver-plated items.