Many comments later (at least 3 pages), I can see that there is a LOT of misinformation regarding the marking of precious metals in the U.S.
I hope I can clear some of this up:
(1) First off, what is a "hallmark" and what is a "quality stamp"?
A quality stamp indicates the amount of precious metal in that piece. The quality stamp "925" or "Sterling" will indicate that this piece is Sterling Silver. Karat gold pieces are quality stamped (14k, 18k, 10k, etc.).
A hallmark is the manufacturer's maker's mark or in the United States, their registered trademark.
(2) What are the U.S. laws regarding stamping sterling silver and other precious metals?
In the USA, The National Gold and Silver Marketing Act does NOT require precious metals to be marked with quality (i.e., "925"). However IF a quality mark is used, the mark MUST be accompanied by a manufacturer's hallmark that is a registered trademark of the manufacturer. If there is ever a question about the content of a piece of jewelry, that manufacturer can be traced using the hallmark that has been stamped on the piece. This accountability is particularly important to gold jewelry----you want to know that you are buying 18k gold as marked, and not 10k gold which is worth one-third less on gold content alone.
In many countries (NOT the U.S.A.) precious metals must have a quality stamp, and jewelry made of precious metal must be submitted to a governmental assay office for destructive testing before being marked and sold.
(3) So Does all Sterling Silver have a mark such as "925" on it?
The answer is NO. There are various reasons why a genuine sterling silver item isn't marked. Perhaps the item is too small. Some narrow gemstone eternity rings for example have no place inside to mark it. Components that are sterling silver, such as beads, open or closed ring findings, or chain, have no room to be stamped. Sterling Silver wire is not stamped.
The cost of getting a registered trademark costs over $1,000, and since BY LAW an item that is stamped 925 MUST have the manufacturer's registered trademark alongside the purity stamp, many small jewelers and Native American jewelers cannot afford this cost for a legal hallmark. Therefore, they will not stamp the item.
Sometimes the quality stamp is lost when an item is re-sized. And sometimes an item is actually stamped lightly, but has been plated with gold or rhodium which fills in the stamp, making it invisible or nearly invisible. I've seen this happen myself many times with rhodium plated items, because sterling silver that's plated with rhodium also has a "barrier" plating between the two metals (such as nickel or copper) and can fill in the quality stamp.
(4) How can I test an item to make sure it's Sterling Silver and not just plated or something else?
You can take the item to a jeweler, who can examine it for you and test it. Or you can buy a testing kit yourself. A small scratch will be made in the item to cut through any plating or lacquer, and then a drop of Nitric Acid will be applied. If it turns green, it is something other than sterling silver (such as brass, so-called nickel silver which has no silver in it, and other low quality metals) because the acid is reacting to a high level of copper. If it turns a creamy color, it is sterling silver.
(5) Are all items marked "925" genuine Sterling Silver?
In the U.S., even though a quality mark is NOT required by law, it is totally illegal to fraudulently mark an item as "925". There are stiff consequences for committing fraud. Although it's possible for someone to purchase a .925 stamp and mark jewelry as sterling when it is not, it's highly unlikely. Plus as mentioned above, it's easy to have the item tested for quality. But that said, I've seen a LOT of so-called "Sterling Silver" jewelry on Ebay that is marked "925" but it is actually silver PLATED, not sterling----the price is very low and their feedback reflects a number of unhappy customers. (For an example, search Ebay for "Sterling Silver 925 Bean Lady's Necklace" - a "kidney bean" charm on an 18" chain for $1.76, free shipping, from China. NOT real sterling silver!)
What IS Sterling Silver?
Sterling Silver is defined as a metal alloy consisted of 92.5% pure silver mixed with 7.5% other metals, the most common being copper. Pure fine silver is 99.999% silver and is considered too soft to securely hold gemstones, so sterling silver looks like pure silver but is harder and more durable. Argentium Sterling Silver is 92.5% pure silver that is alloyed with 1.2% germanium and 6.3% copper---the smaller percentage of copper makes this more tarnish resistant.
Other possible markings include "Mexican Silver", "German Silver", "Indian Silver", "Alpaca Silver" or even simply "Silver" and do not guarantee any silver content. In fact, "German Silver" and "Alpaca Silver" contain NO silver whatsoever and are actually alloys of zinc, nickel and copper.
What About Pure or "Fine" Silver?
Sometimes artisans use pure Silver (or "Fine" Silver) which will contain more silver than "regular" Sterling Silver--no alloys are added. While Sterling is 92.5% Silver, Fine Silver is 99.9% pure. Although Silver is considered to be too "soft" for jewelry, it really is too soft to hold gemstones or hold its shape in a ring worn daily. Fine silver beads and charms are beautiful, with a more brilliant white "silver" color, and are far more resistant to tarnish. In Thailand, the Karen Hill Tribe makes and sells fine silver components and NONE are hallmarked or quality stamped. They guarantee their silver to be at least 97% pure---taking into account the use of solder. I also make pure silver charms myself by melting pure silver grain, which I purchase at Rio Grande Jewelry which is a supplier that I trust, and I don't mark the charms. But I guarantee they are 99.99% pure fine silver.
- Sterling silver must be at least 92.5% silver.
- US law does NOT require precious metal to be marked with a quality stamp.
- Some European countries do require marking. Many tourists visiting the US will question goods sold without markings that indicate precious-metal quality.
- US law requires a maker's mark in the form of a hallmark or registered trademark in addition to the quality mark if the goods are quality marked. The name of the artist or manufacturer may now be used for this.