Where these rules come from
Until 2007 a UK article combining two precious metals could not be hallmarked as one piece in the way it is now. An amendment to the Hallmarking Act that year allowed mixed-metal articles to be marked, and the four UK assay offices set out how they apply it in their Hallmarking Guidance Notes, published on GOV.UK in November 2022. This tool follows pages 4 and 9 to 11 of those notes, read in October 2026. The notes say plainly that they are practical guidance and not a legal interpretation, and the assay office that receives a piece decides how it is marked.
Two conditions come before any mark. The first is visual: an article of more than one precious metal can only be marked if, in the assay office’s opinion, an ordinary person can tell which part is which metal. A ring whose platinum and white gold look the same to the eye fails it, and no calculation can answer that question, which is why the tool does not try. The second is a floor: every precious part must be at least the minimum legal fineness for its metal, which is platinum 850, gold 375, palladium 500 and silver 800 parts per thousand, the figures in section 22 of the Act.
The least precious metal carries the full hallmark
A full UK hallmark is three compulsory marks: the sponsor’s mark, the assay office mark and the metal and fineness mark. On a mixed piece only one full hallmark is struck, and it belongs to the least precious metal present, taking the order silver, palladium, gold, platinum. It is normally struck on that metal. If that is not practicable it may go on the more precious one.
Every more precious metal in the piece then receives its fineness mark only, struck on its own part. A gold ring with a platinum head therefore shows a full gold hallmark on the shank and a lone platinum 950 on the head. That is the usual answer to the question of why a ring has two numbers on it. The two numbers do not conflict and neither is a correction of the other: each describes the metal it is struck on.
The order also explains a pattern that can look odd at first. A silver bangle with small gold details takes a full silver hallmark, even though the gold is the more valuable metal, because the full hallmark follows the least precious metal, not the most valuable or the heaviest.
Two golds are not two metals
A piece made of 9 carat and 18 carat gold is not a mixed-metal article. The notes say two standards of the same precious metal are not regarded as mixed metals, and the hallmark for the lower standard is applied. So a ring with a 750 head on a 375 shank is hallmarked 375 throughout. The tool shows this when two parts of the same metal are entered at different finenesses. A hallmark is a guarantee of the fineness the whole of that metal meets, and the lower figure is the one the whole piece can meet.
Small parts and the anomalies
Small components can make the standard arrangement impossible, and the notes give a sequence of fallbacks. If the fineness marks cannot be struck on the more precious metals, they may be struck on the less precious ones. If that is not practical either, they may go on another precious metal part. Failing both, only the full hallmark of the least precious metal is struck on its part and the other marks are omitted. A piece showing only one hallmark can therefore still contain a second precious metal.
One exception runs the other way. A platinum article with small parts of gold that is not white gold, at 750 or higher, may be hallmarked with a platinum full mark and the gold fineness mark, which can go anywhere on the article. It does not apply to 585 or 375 gold, and the gold parts must not exceed half the article’s total weight. The tool checks the three conditions it can check from the figures entered: whether the gold is white, its fineness, and its share of the weight. Stones and other materials count towards an article’s total weight too, so the share shown is of the metal weights entered.
Base metal and +METAL
A precious metal can also be combined with base metal such as stainless steel, titanium or brass. The notes allow this to be hallmarked if the base metal parts are clearly distinguishable from the precious metal by colour or texture and clearly visible by their extent. The hallmark goes on the precious metal part only, with the word +METAL beside it, so there must be room for both. Wherever practical, METAL or the name of the metal is also struck on the base metal part. When there is more than one precious metal as well as base metal, the mixed precious metal rules apply on top. Concealed base metal that does a technical job, such as a continuous spring inside a bangle, is marked +SPRING instead and is not modelled here.
The exemption weight on a mixed piece
UK hallmarking only applies above the exemption weights: 0.5 g for platinum, 1 g for gold and palladium, 7.78 g for silver. On a mixed piece the notes take the exemption weight of the higher precious metal and compare it with the total weight of all the precious metal. Their own example is 0.5 g of gold with 3 g of silver. The higher metal is gold, so the line is 1 g, and the total of 3.5 g is over it, so the article is not exempt, although neither metal alone would have needed marking. A test on this site reproduces that example.
Two details matter at the margin. Where base metal is present, page 4 of the notes says the exemption weight is based on the total metal weight, base metal included, so the tool adds it. And the Act’s wording is “less than”, so a piece at exactly 1 g of gold is not under the line. The exemption metal the tool uses is derived from the notes’ order, and a test holds it equal to the paragraph that the Act’s own Schedule 1 exclusions select for every combination of metals, so the two sources agree here rather than being assumed to. The exemption weights tool covers the weight rule on its own.