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A sterling silver object that is to be sold commercially is, in most countries, stamped with one or more silver hallmarks indicating the purity of the silver, the mark of the manufacturer or silversmith, and other (optional) markings to indicate date of manufacture and additional information about the piece. In some countries, the testing of silver objects and marking of purity is controlled by a national assayer's office.
Hallmarks are applied with a hammer and punch, a process that leaves sharp edges and spurs of metal. Therefore, hallmarking is generally done before the piece goes for its final polishing.
The hallmark for sterling silver varies from nation to nation.
One of the most highly structured hallmarking systems in the world is that of the United Kingdom, (Scotland, England, Wales and Northern Ireland), and Ireland. These four nations have, historically, provided a wealth of information about a piece through their series of applied punches:
The series of hallmarks described above are still in use in today.
However, there are two silver hallmarks that have been discontinued:
The French assay mark for sterling silver is the head of the goddess Minerva. In fact, the French standard for sterling silver is higher than that of other nations, requiring a silver content of 950 parts per thousand, or 95% silver. Silver items with a slightly lower grade of silver, 800 parts per thousand, are marked with the head of Minerva, next to which is a "2".
French silver made for export carries an assay mark in the shape of the head of Mercury, along with a number to indicate the millesimal fineness: "1" for .920, "2" for .840 and "3" for .750.
French silver also is punched with the mark of the maker.
In the early United States, no national assaying system was adopted, although the city of Baltimore did maintain its own assay office between 1814 and 1830. Prior to the general adoption of sterling silver as the standard of purity in 1868, silver was generally obtained from the melting of coins. Since these could vary considerably in purity, from around .750 millesimal fineness to around .900, silver known as "coin silver" varies in purity. Silver at that time was sometimes marked "COIN" or "PURE COIN", but can also be without a standard mark altogether. After the adoption of the sterling standard, pieces were marked with "STERLING", the number "925" or the notation "925/1000".
While American manufacturers did not apply assay marks, city marks or date marks, they did apply a maker's mark. This is generally not done today. The old hallmarks were as unique as today's logos, and disputes often arose when one company copied another's stamp.
"In the USA, The National Gold and Silver Marketing Act does not require precious metals to be marked with quality. However, if a quality mark is used, the mark must be accompanied by a manufacturer's hallmark that is a registered trademark or the name of the manufacturer. If there is ever a question about the content of a piece of jewelry, the manufacturer can be traced using the hallmark stamped on the piece....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." 
Between 1867 and 1933, Austria-Hungary and later, Hungary used the crescent moon crowned head of antique greek heroine Diana as the hallmarking symbol of legal silver alloys. The head was encircled by a frame, optionally composed of convex, concave and straight lines. One concave line represented 140/1000 fineness, a straight one 150 and a convex one 160. For example, a Diana head within a frame made in the shape of a 5-petal flower represented 5x160 = 800 thousands fineness, a local silver standard commonly used in eating forks and spoons. Meanwhile a hexagonal frame represented 900 fine silver. The same logic was also used to frame gold hallmarks.
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