Fine jewellery is chosen for its beauty, its meaning and the way it feels when worn. Yet some of its most important details are among the smallest.
A hallmark is one of them. Discreetly applied to the precious metal, it provides independent confirmation of its fineness—the proportion of pure precious metal it contains.
At Semper, our solid 18-carat gold creations are hallmarked at the London Assay Office. Our hallmark includes the Common Control Mark, also known as the CCM. Understanding these marks offers a closer connection to the piece you choose and the assurance behind it.
What is a hallmark?
A hallmark is a set of marks applied by an independent assay office after testing precious metal.
It confirms that the metal meets the stated standard of fineness. For an 18-carat gold piece, that standard is 750 parts of pure gold per thousand, or 75%.
This is different from a brand engraving or a simple “18K” stamp. A recognised hallmark provides independent verification rather than relying solely on the seller’s description.
The UK hallmarking system has protected buyers for centuries, providing an established way to verify precious-metal content.
What does a London hallmark mean?
A London hallmark identifies the London Assay Office as the office responsible for testing and hallmarking the piece.
Its identifying symbol is the leopard’s head, a mark with a history stretching back to 1300.
For the wearer, this provides independent assurance that the precious metal has been assessed against a recognised fineness standard.
Hallmarking in London identifies where this verification took place. It does not, by itself, establish where a piece was designed or manufactured.
What is the Common Control Mark?
The Common Control Mark (CCM) is an international hallmark used under the Convention on the Control and Marking of Articles of Precious Metals, also known as the Hallmarking Convention or Vienna Convention.
The CCM uses scales surrounding a fineness number. On Semper’s 18-carat gold pieces, the CCM shows 750 within the scales. Convention member countries recognise qualifying articles bearing the CCM, supporting their acceptance across those markets. (hallmarkingconvention.org, gov.uk)
The CCM is distinct from the separate 750 fineness mark in Semper’s full hallmark. Both relate to the gold standard, while the other marks identify the sponsor and the London Assay Office.
How to read the hallmark on a Semper piece:
Semper’s hallmark is made up of four marks. In order, they are:
-
SEM: the sponsor’s mark
This identifies Semper as the registered sponsor responsible for submitting the piece for hallmarking. -
The scales: the Common Control Mark
This is the international Convention mark. On Semper’s 18-carat gold pieces, it contains the number 750. -
750: the fineness mark
This states that the gold contains 750 parts pure gold per thousand, or 75%. -
The leopard’s head: the London Assay Office mark
This identifies the office that tested and hallmarked the piece.
Together, these marks show who submitted the piece, its verified gold fineness, the use of the Common Control Mark and the London Assay Office responsible for hallmarking.
What does 750 mean?
The number 750 means that 750 parts out of every thousand are pure gold. This is the recognised fineness standard for 18-carat gold.
The remaining 25% consists of other metals in the alloy. These metals help create the different gold colours and contribute to the properties needed for jewellery.
Whether you choose yellow, white or rose gold, the proportion of pure gold remains the same in an 18-carat alloy. The colour changes; the fineness standard does not.
You can explore how these colours influence the character of a piece in our guide to yellow, white and rose gold.
Does every hallmark include a date letter?
Some UK hallmarks also include a date letter indicating the year in which the piece was hallmarked.
The date letter has been optional since 1999, so a modern hallmark can be complete without one.
You may also see additional traditional or commemorative marks. Their presence can add information, but they do not replace the compulsory marks.
Is a 750 stamp the same as a hallmark?
The number 750 is a statement of fineness, but it is not, on its own, a complete UK hallmark.
A number stamped into the metal does not provide the same information as the full set of marks. On a Semper piece, the sponsor’s mark, CCM, fineness mark and London Assay Office mark each have a distinct role.
When examining a piece, look for the complete set rather than relying solely on “Au750” or “18K”.
What does hallmarking confirm?
Hallmarking confirms the fineness of the precious metal.
Other qualities of a piece—such as its design, finishing, gemstone quality and the security of its settings—require separate consideration. A hallmark does not grade a diamond or certify a coloured gemstone.
For a considered purchase, hallmarking sits alongside a clear description of the materials, gemstone specifications and aftercare available. Each provides different information about the piece.
Where can you find the hallmark?
Hallmarks are usually positioned discreetly so they can be inspected without interrupting the design.
On rings, they are commonly found inside the band. On necklaces and bracelets, they may appear near the clasp, on a small attached tag or on another suitable part of the piece.
The exact position depends on the design and the available surface. Because the marks are small, a magnifying glass or jeweller’s loupe can make them easier to read.
Hallmarks may be struck into the metal or applied by laser.