Why gold carries a number at all
You found 375, 585 or 750 inside a ring, and you want to know what it says about the gold. The short answer is that it tells you how much of the metal is gold. That matters because the gold content, and the other metals mixed with it, affect how durable the ring is and what colour it can be 1.
Why were these marks invented? Gold hallmarks began as a way to show purity. They combined the mark of the assay office that tested the piece with its fineness or caratage. An assay office is an official centre that tests precious metals. Hallmarking was Europe’s earliest form of consumer protection, dating back to the 1200s. The word itself comes from Goldsmiths’ Hall in London and its official marks 2.
Why can a full hallmark carry so much weight? The Goldsmiths’ Company Assay Office in London, in the United Kingdom, explains that a hallmark means the piece has been independently tested and meets the legal standards of purity where it was marked. Purity is also called fineness. The marks also tell you where the piece was hallmarked, what it is made of and who sent it for testing 4.
Why the numbers are parts per thousand
Why use three digits instead of a carat number? Fineness is another way to express gold content: purity in parts per thousand, usually stamped without the decimal point 1. A 750 stamp means 750 parts in every 1,000 are gold, which is 75%.
Why do carats count differently? The traditional carat scale counts in 24ths. On that scale, 24 carat means pure gold with no other metals. So 18ct (18K) gold is 75% gold and 25% other metals, often copper or silver 1. Gold carat measures purity. It is not the same as the carat used to weigh diamonds.
Here is how the common stamps line up:
- 375 = 37.5% gold = 9ct
- 417 = 41.7% gold = 10ct
- 585 = 58.5% gold = 14ct
- 750 = 75% gold = 18ct
- 999 = 99.9% gold = 24ct 1
You may also see 916, which means 91.6% gold. It is one of the gold finenesses listed for the international hallmark explained further down 3.
Why 14ct is stamped 585, not 583
Why does the 14ct number look slightly off? Strictly, 14 parts in 24 works out at about 583 parts per thousand. Most manufacturers adopted the European practice of making 14ct gold slightly over 14 carat, so 585 is the usual mark, though 583 also means 14ct 1.
Why your ring isn’t pure gold, and what the rest is
Why mix gold with other metals at all? Pure gold is soft, and alloying makes it more durable. An alloy is a blend of metals melted together. The added metals can also change the colour: white gold can use palladium or silver, and rose gold uses copper. Because fineness counts the gold in every 1,000 parts, a lower number means more of these other metals 1.
What that changes in colour, wear and feel is covered in 9ct vs 14ct vs 18ct gold.
Why you may see more than one mark
Why is the number sometimes surrounded by little symbols? A full hallmark is a set of marks, and each one answers a different question. Under the international treaty described below, a full hallmark has a maker’s or sponsor’s mark, an assay office mark, a fineness mark and the Common Control Mark 5.
- Fineness mark: the number, showing precious metal content in parts per thousand. In the United Kingdom’s London system, the shape of the shield around it shows the metal type.
- Assay office mark: shows which assay office tested and hallmarked the piece.
- Responsibility mark: the London assay office in the United Kingdom calls it the sponsor’s mark, and it is sometimes informally called a "maker’s mark". Its purpose is to show who is responsible for the piece, not to name the manufacturer 4.
The Hallmarking Convention notes that some countries also use the name sponsor’s mark 3. Historically, marks showing which goldsmith made a piece were added after the purity and assay office marks 2.
Why some rings carry a balance-scale symbol
Why does an international mark exist? An international treaty, the Convention on the Control and Marking of Articles of Precious Metals, was signed in Vienna in 1972 and came into force in 1975. Items carrying its hallmark from one member state are recognised in other member states without being hallmarked again 5.
Its symbol is the Common Control Mark (CCM), the first international hallmark. National assay offices apply it after testing fineness with agreed methods, together with an assay office mark and a responsibility mark. One version, the Type 1 CCM, shows the metal and its fineness in parts per thousand, and the shield shape shows which metal it is 3.
For gold, the CCM shows a balance scale over two intersecting circles 2. The gold finenesses listed for the CCM include 999, 916, 750, 585 and 375 3.
Why tiny stamps are hard to read, and how to read them
Why do the marks seem so hard to see? They are very small. The London assay office in the United Kingdom describes its standard ring hallmarks as up to 0.75 mm high 4. A magnifying glass or a jeweller’s loupe, a small folding magnifier, makes them easier to read. Then work through the marks in this order:
- Find the number first. It is usually stamped without the decimal point, so .750 reads as 750 1.
- Look at the outline around it. In the United Kingdom’s London system 4 and on the Type 1 CCM 3, the shield shape shows which metal it is.
- Check beside it for other symbols: an assay office mark, a responsibility mark or the CCM balance scale.
- Know when the number is a minimum. Under the rules of the London assay office in the United Kingdom, an item is marked to its lowest standard, so the whole piece is no less fine than the number shown 4.
Downsides: when a gold mark is not a guarantee
Why can’t every stamp be taken at face value? Each nation has its own requirements and its own hallmarks. In some countries hallmarking is voluntary, and manufacturers apply their own marks 2.
Where the maker applies the number, the stamp alone does not show whether an independent test took place. Even within the international system, some countries let the manufacturer apply the fineness mark before the piece is assayed and marked 3.
The word "gold" has no single global meaning either, because the minimum caratage that can be called gold varies by country 1.
A fineness mark shows precious metal content, and in some systems the metal type through its shield shape, but it says nothing about any stones set in the ring. A full set of marks adds where the piece was hallmarked and who sent it for testing 4. So a lone number is a useful clue, while a full set of marks tells you more.
Why your number answers your question
Why does one small stamp matter so much? Because it tells you the gold content in a single line: 375 means 9ct gold, 585 means 14ct and 750 means 18ct 1. Other symbols beside it can show where the piece was tested and who is responsible for it.
If you are choosing a new ring and want to compare 9ct, 14ct and 18ct gold, Ralph Jacobs offers a free consultation, booked online at bookings.ralphjacobs.org from any country. If you are also weighing up gold against other metals, see white gold vs platinum.
Frequently asked questions
They differ in gold content. 750 is 18ct, with more gold. 375 is 9ct, with more of the other metals, which affect durability and colour 1. Which suits you depends on what you value. See 9ct vs 14ct vs 18ct gold for the differences.
Strictly, 14 parts in 24 works out at about 583 parts per thousand. Most manufacturers adopted the European practice of making 14ct gold slightly over 14 carat, so 585 became the usual mark. Both numbers indicate 14ct gold 1.
Not necessarily. The responsibility mark, called the sponsor’s mark by the London assay office in the United Kingdom and informally a maker’s mark, shows who is responsible for the piece. Its purpose is not to identify the manufacturer 4.