Japanese and Western Metal Marks Compared: K18, Pt900, SV925, Hallmarks and Watch Case Metals

How to use this guide

Every statement here is drawn from a published source listed under References. We paraphrase throughout, and where we quote, the phrase is short and credited. Legal statements are given as the relevant authority presents them, and we separate three things that are often blurred: what a law requires, what an industry body recommends, and what is merely customary in the trade. Nothing here is legal advice, and where a point cannot be confirmed from a published source, we leave it out or label it as unverified.

Japanese terms appear in romanised form only. Stamps written in Latin letters and numerals, such as K18 or Pt900, follow the Japan Jewellery Association (JJA) notation.

Three ways to say purity

Purity is expressed in three interchangeable languages. Karat counts parts of gold in twenty-four. Millesimal fineness counts parts per thousand, so 750 means 750 parts of gold in every 1000 of alloy. Percentage is simply the millesimal number divided by ten. Japanese trade practice uses all three, and the JJA guidelines tie them together: the notation is the chemical symbol plus the fineness number, such as Au750 or Pt900, and for gold the K form is also accepted, so that K24 equals 999, K18 equals 750, K14 equals 585, K10 equals 416, K9 equals 375 and K8 equals 333. The same page notes that 990 has no karat equivalent.

The JJA guidelines present the fineness classes as drawn from JIS H6309:2022, the Japanese Industrial Standard for the subject. In that scheme the recognised gold classes run 999, 990, 916, 833, 750, 585, 416, 375 and 333, the platinum classes 999, 990, 950, 900 and 850, the silver classes 999, 990, 958, 950, 925 and 800, and the palladium classes 999, 990, 950 and 500.

Jun-kin and the question of 1000

Jun-kin, literally pure gold, is the trade term for 24 karat. A retailer's encyclopedia describes the commercial expectation as 999.0 or higher, with 999.9 reserved for investment ingots, and notes that Japanese makers and dealers have historically self-marked with a K prefix rather than relying on a state assay. The JJA guidelines align with the 999 threshold: the word pure may be used at 999 or above, and a 1000 purity mark is not permitted. Older Japanese platinum and silver pieces may nevertheless carry Pt1000 or 1000, and one dealer column explains that Pt1000 is an older mark now replaced by Pt999 because true one hundred per cent purity is technically unattainable.

What marks mean in Japan

The statute

The English text of the Precious Metals Control Law held by Nagoya University's Japanese Law database concerns the refining and sale of bullion, the handling of dental-use bullion and gold transactions. It defines refined bullion as 999 for gold and silver and 998 for the other listed metals. Our reading found no article that obliges makers to hallmark jewellery or other finished goods. That database translation is dated, and we have not been able to confirm which amendments are in force, so we state only what the text contains: a control regime for bullion, with no marking clause.

The Japan Mint hallmark

The Japan Mint is an independent administrative institution with its head office in Osaka. Beyond coinage it tests ores and certifies the fineness of precious metal wares, which is to say it hallmarks them. Its English operations page lists two services under Hallmark, Analysis and Testing: fineness certification with Mint certification marks, and fineness certification without them. A fineness certification branch was established in 1929, and the Wikipedia article on silver hallmarks likewise dates Japan Mint assaying and hallmarking of silver articles from 1929.

A trade encyclopedia describes the hallmark as voluntary rather than compulsory, applied after X-ray fluorescence testing, with cupellation or fire assay where needed, and notes that much domestic jewellery carries only a maker's quality stamp. We treat that as a trade description, not an official statement: the Mint page lists the services but not the rules. The JJA guidelines offer indirect confirmation of the voluntary character, since they allow gold and platinum pieces bearing the Mint hallmark to omit the metal type and fineness, and silver pieces to omit the fineness.

The JJA guidelines

The JJA is a public-service body representing the jewellery trade, with roughly 840 corporate members according to its own English page, spanning importers, exporters, makers, wholesalers and retailers. Its marking guidelines are what we would call the working rulebook of Japanese jewellery stamping. The page does not say whether they carry legal force, and we therefore describe them as industry guidelines. Their key provisions, as we read them:

  • Platinum may be so labelled from 850 upward, gold from 333 upward and silver from 800 upward.
  • Silver at 925 may be stamped 925 alone, or Sterling, or Sterling Silver. The words SV, Silver or SILVER without a number are acceptable only at 925 or above.
  • Other silver alloys carry symbol plus number, for instance Ag958 for Britannia silver, Ag900 for coin silver and Ag835 for Dutch silver.
  • Secondary metals are shown in brackets after the primary, as in Ag900(Pt).
  • Colour codes for gold are WG, YG, GRG and PG. A colour name must reflect the alloy itself, not plating; a rhodium-plated coloured alloy may not be called white gold if the colour difference exceeds 14 on the CIELAB scale.
  • Antique, historical and nugget jewellery may lack any fineness mark.

How to read a Japanese piece

Begin where the maker would have stamped: inside the shank of a ring, on the clasp, on a bail, or beside the catch. A dealer's guide to platinum recommends a ten times loupe and raking light to bring worn characters up. Then read in this order.

  1. Metal and number. Au, K, Pt, Ag, SV or Pd, followed by the fineness. A stamp reading Pt900 is platinum at 900 parts per thousand. A bare 750 is usually K18 gold, a point the same dealer column makes in warning against confusing it with platinum.
  2. The Mint hallmark. If present, it can stand in for metal type and fineness on gold and platinum, and for fineness on silver. Fineness classes the Mint is reported to certify include platinum 850, 900 and 950, gold 375, 585, 750 and 916, and silver 925 and 950, according to the trade encyclopedia.
  3. Surface and construction codes. GP, RHP, PTP, WGP, PGP and AGP denote plating; an IP ending denotes ion plating; GF and RG denote gold clad; a suffix F denotes clad silver or platinum; and [H] denotes a hollow item whose outer layer fully covers it.
  4. Old and unusual notations. Pm is an old platinum notation without a purity number and may indicate platinum below 85 per cent. PTF or PR indicates platinum filled or plated over a base metal. Pt800 is rare in Japan because the JJA does not permit it to be called platinum jewellery; it can indicate an older or overseas piece. All three points come from the dealer column and the JJA text together.
  5. The maker's quality stamp. Much domestic jewellery carries only the maker's own stamp. The JJA text treats non-precious functional parts, such as springs and pin backs, as exempt from marking, and excludes their weight from the stated weight.

Anatomy of a hallmark

The word hallmark comes from Goldsmiths' Hall in London, where official testing was centred. A hallmark proper is an assurance from an independent authority, in contrast with a maker's mark, which is the maker's own statement. In the British system a complete hallmark has three compulsory parts: the sponsor's or maker's mark, which the London Assay Office guide says must contain at least two letters within a surround; the metal and fineness mark, in which the shape of the surround indicates the metal and a number gives parts per thousand; and the mark of the assay office that tested the piece. The date letter has been optional since 1999, and pictorial marks such as the sterling lion are likewise optional, according to the UK Business Companion guide.

A short history in marks

The Goldsmiths' Company and the London Assay Office between them date the leopard's head requirement for silver to a statute of 1300, the maker's mark to 1363, the date letter and a permanent assay office at the Hall to 1478, and the lion passant standard mark to 1544. The sterling standard was confirmed in 1576. The Britannia standard, with 95.84 per cent silver, was introduced in 1697 to discourage the melting of coin, which is why the 958 figure persists in modern lists. Assay offices were established at Birmingham and Sheffield in 1773, and a platinum mark, described as an orb and cross, arrived with the Hallmarking Act that took effect in 1975, the year the United Kingdom also joined the international convention. Since 1999 the sponsor's, standard and town marks have been compulsory and the date letter voluntary.

Country by country

The table below sets out what each system requires, as stated by the authority cited. Where no authoritative page was found, we say so rather than infer.

The Convention in a paragraph

The Hallmarking Convention, signed in Vienna in November 1972, lets national assay offices apply a Common Control Mark that other members accept without retesting. The convention's own site describes Type 1, in which the shield shape indicates the metal and the fineness is shown in parts per thousand, and Type 2, introduced in 2019, an octagonal conformity mark applied beside separate metal and fineness marks. Each member sets its own legal standards, and five are legal in all Contracting States: Pt950, Au750, Au585, Ag925 and Ag800. The member list in the UK Business Companion guide includes Switzerland, the UK, Italy, Ireland, Austria and others, and does not include Japan.

The United States

The Federal Trade Commission's Jewelry Guides, set out in 16 CFR Part 23, define when metal terms are acceptable. In the text cited, sterling or solid silver requires at least 925 parts per thousand, coin silver at least 900, and the word silver alone is misleading unless a fineness figure precedes it. An unqualified platinum claim requires at least 950; platinum marks at 850, 900 and 950 are acceptable when preceded by the number; between 500 and 850 a full composition disclosure is expected; and below 500 the word platinum may not be used. Under Note 2 to the quality marks section, a person who applies a quality mark, or imports an article carrying one, must also apply a trademark or name. The Guides are guidance, whereas the stamping tolerances derive from the National Stamping Act.

Platinum, palladium and silver

Platinum is the metal on which Japanese and Western practice diverge most in nomenclature, though not in numbers. The JJA permits the word platinum from 850 upward. The British fineness list recognises 999, 950, 900 and 850. The Swiss Act lists the same four classes. The United States allows 850 to 950 with the number shown but reserves an unqualified platinum claim for 950 and above.

Palladium

Palladium has been used in jewellery since 1939 as an alternative to platinum, and is one of the three common whitening metals in white gold, together with nickel and silver. UK assay offices have hallmarked it since January 2010 at 500, 950 or 999, according to the palladium article, and the Swiss and JJA lists carry the same classes. The Convention site cautions that palladium is not accepted in every member state. Seiko catalogue codes also use PDP for palladium plating.

Silver in Japanese practice

Japanese silver stamps most often read SV925, Silver, Sterling or 925, all of which the JJA accepts at the sterling threshold. Silver from the Meiji export period carries no consistent system: the Metropolitan Museum entry for a five-piece Meiji tea and coffee service describes it as sterling silver but lists no marks, which illustrates how often object records omit them.

Plated, filled and rolled gold

These terms describe a thin layer of gold over a base metal. The rules differ in how precisely they define the layer. In the JJA scheme, gold-clad items use GF, for Gold Filled, if the gold alloy is at least one twentieth of the mass, and RG, for Rolled Gold, if less. Plating codes include GP for gold, RHP for rhodium, PTP for platinum, WGP for white gold, PGP for pink gold and AGP for silver, with thickness in micrometres after the code, for example GP 3 micrometres.

Two cautions follow. First, the American rules are written as unfair or deceptive practice standards, and the ratios above are acceptable examples, not a mandatory stamp. Second, the Wikipedia gold filled article contradicts itself on whether GF is an acceptable abbreviation, stating that gold filled is never abbreviated as GF while showing stamps such as 1/20 14kt GF. We rely on the JJA text for Japanese usage, where GF is explicit.

Watch case metals

Watches add two layers of complexity: a case may be solid precious metal, a steel or titanium alloy, or a plated base metal, and the stamp on the back may follow a catalogue code rather than a legal mark. Switzerland is the clearest legal case. Its Federal Act states that watch cases of precious metal are subject to official control before sale, and the Federal Office page confirms one official mark, the head of a St Bernard dog, used for all precious metals and fineness classes, with the assay office's own symbol at a designated position. Other precious metal articles may be submitted voluntarily.

The Seiko codes come from a reference table compiled from catalogues, whose compiler warns that the case back stamp often, but not always, shows the same material. Treat catalogue codes as identification aids and stamped marks as evidence of what the case actually contains.

Titanium and steel carry no precious metal hallmark. Titanium is about 4.5 grams per cubic centimetre and melts at 1668 degrees Celsius.

Density and colour

Density is the quickest physical corroboration of a metal, and colour helps a trained eye. The figures below come from reference articles on each element, at 20 degrees Celsius.

Gold and tungsten have almost identical densities, about 19.3 and 19.25, which is why the gold article records that tungsten has been used to counterfeit gold bars. Density alone is therefore a corroboration, not a proof.

See the marks

We do not embed or reproduce photographs of marks. The strip below links to reference pages. Credit and licence lines are given as shown on each page; where none is shown, no reuse is assumed.

Reading a provenance trail

Provenance is the documented chain of a piece's history. Marks are one strand of it, and it helps to be exact about which strand they are.

What marks can show

  • A fineness number states the maker's or assayer's claim about metal content. With an official hallmark, an independent authority stands behind that claim, whereas a maker's mark is the maker's own statement.
  • In a British hallmark, the sponsor's mark names who placed the piece on the market and the assay office mark names where it was tested.
  • A date letter, where present, indicates the year of assay. Its style, case and surround must be read together. Because the date letter has been optional since 1999, its absence on modern British work is unremarkable.
  • A Mint hallmark in Japan indicates that the Mint tested the piece. The JJA lets it stand in for metal and fineness stamps.

What marks do not show

  • A catalogue code is not a legal mark. Seiko codes are compiled from catalogues and the stamp on the case back often, not always, matches.
  • No mark at all is not a verdict. The JJA says antique, historical and nugget pieces may lack any fineness mark, and the dealer guide describes Pm and other older notations that predate present rules.
  • A fineness stamp is not an age statement. Notations such as Pt1000 have been superseded by Pt999 in current practice, so the notation can help date a piece loosely but cannot fix it.
  • A weight exemption is not a purity statement. In Britain, items below the exempt weights need no hallmark, yet the British Hallmarking Council still advises describing them with a fineness.
  • A mark on a part is not a mark on the whole. The FTC guidance requires disclosure of which part a quality mark covers where that matters, and the JJA marks hollow and weighted items separately.

Building the trail

Photograph the stamp line under magnification, record every character as stamped, and match each element against the tables above. Then add any assay certificate, maker's box, papers and dated records. A stamp is a statement; a trail is the set of statements that agree with one another. Where they do not agree, the disagreement is itself information.

Where the records disagree

The references do not always agree, and we prefer to show the disagreement than to smooth it over.

  1. K10, K20 and K14 arithmetic. JJA gives K10 as 416, and ISO 9202 and the Carat article give 417. The Carat article gives 20 karat as 834 where the JJA class list shows 833, and notes that 14 karat is exactly 583.3 though marked 585.
  2. The motif on the Japan Mint hallmark. A trade encyclopedia describes a rising sun with characters for the metal. The Wikipedia silver hallmarks article says the marks feature the national flag. No official Mint page describing the motif is cited, so no drawing of it is offered.
  3. Whether 1000 is a valid mark. The trade encyclopedia lists platinum and silver at 1000 among common Mint finenesses. The JJA guidelines state that a 1000 mark is not permitted. A dealer column adds that Pt1000 is an older mark. The likeliest reconciliation is that old stock and newer rules coexist, which is not confirmed.
  4. Convention symbols. Wikipedia describes balance scales for gold, a diamond shape for platinum and an M shape for silver; the convention's own site describes Type 1 shield shapes and a 2019 octagonal Type 2. The official site should govern.
  5. Palladium dating. The palladium article gives January 2010 for UK hallmarking, while the Goldsmiths' summary places it only in the 2000s and 2010s.
  6. Gold filled abbreviations. The Wikipedia gold filled article says GF is never used while showing GF stamps; the JJA text uses GF without qualification.
  7. ISO and JIS currency. The ISO 9202:2019 page shows the edition withdrawn with revision by ISO 9202:2026, while the JJA cites JIS H6309:2022. The later ISO text is not compared here.
  8. Binding force of the JJA text. The page presents the rules without saying whether any are enforceable. We do not claim they are.

Questions readers ask

Is hallmarking compulsory in Japan?

For finished jewellery, the pages cited show no general obligation. The Precious Metals Control Law text concerns bullion and contains no marking clause. The Japan Mint hallmark is described by a trade reference as voluntary, and the JJA guidelines treat it as an optional substitute for separate stamps. Because the translation is dated, confirm current law with a qualified adviser.

Does K18 mean the same as 750?

Yes. The JJA guidelines equate K18 with 750, meaning 75 per cent gold. The K form is written before the number and the Au form after the symbol, so K18 and Au750 are the same claim.

Is Pt900 better than Pt950?

Neither is better in every respect. Pt950 holds more platinum and is a recognised class in every system compared here. A dealer column says Pt900 is harder and easier to work, which suits intricate settings. Both are above the 850 threshold at which the JJA permits the word platinum.

What does SV925 mean?

Sterling silver at 925 parts per thousand, or 92.5 per cent silver. The JJA accepts SV, Silver or Sterling for pieces at 925 or above. In the United States, sterling likewise requires at least 925, and the word silver alone is not enough without a preceding fineness number.

Is GP the same as gold filled?

No. GP is gold plating, with thickness stated in micrometres in the JJA scheme. GF is gold clad at one twentieth of the mass or more, and RG is clad at a lower proportion. In the American Guides, gold filled and gold plate carry different minimum layer fractions.

Do Swiss watches carry a hallmark?

If the case is gold, silver, platinum or palladium and the watch is sold in Switzerland, yes: official control is required, and the mark is the head of a St Bernard dog with the assay office's own symbol. Steel and titanium cases carry no precious metal hallmark.

Can a magnet or a scale prove purity?

No. A dealer guide notes that platinum is not magnetic, but that a lack of reaction does not prove authenticity, and the gold article shows that tungsten can mimic gold density.

Why does a Japanese stamp sometimes show no number?

Because a Mint hallmark can stand in for the metal type and fineness on gold and platinum, and for fineness on silver, or because the piece is antique or a nugget piece. The absence of a number is a prompt for further reading, not an indictment.

To see how these marks appear on pieces in our care, browse Japan gold jewellery, silver jewellery, the wider jewellery collection, collectible watches and Rolex.

This is the first part of our reference. Part two covers diamonds, pearls and gemstones: grading terms, reports and certificates.

References

  1. Japan Jewellery Association, precious metal jewellery marking guidelines (metal guide): https://jja.ne.jp/lib/rules/pdf/metalguide.pdf
  2. Japan Jewellery Association, about the association: https://jja.ne.jp/english/whatis/
  3. Japan Mint, hallmark, analysis and testing: https://www.mint.go.jp/eng/operations-eng/hallmark_etc-eng
  4. Wikipedia, Japan Mint: https://en.wikipedia.org/wiki/Japan_Mint
  5. Precious Metals Control Law, Japanese Law Translation database, Nagoya University: https://jahis.law.nagoya-u.ac.jp/lawdb/l/325a0128en
  6. Skyjems, encyclopedia entry on the Japan Mint hallmark: https://skyjems.ca/pages/encyclopedia-japan-mint-hallmark
  7. Skyjems, encyclopedia entry on junkin: https://skyjems.ca/pages/encyclopedia-junkin
  8. Asiamedals, fineness classifications and Japanese Mint certification marks (captions only): https://www.asiamedals.info/threads/fineness-classifications-and-japanese-mint-certification-marks-of-precious-metal-products.13081
  9. Kaitori Daikichi, platinum marks column: https://www.kaitori-daikichi.jp/column/gold-platinum/platinum/post-5115131/
  10. GOV.UK, hallmarking fineness guidance: https://www.gov.uk/government/publications/hallmarking-fineness-guidance
  11. British Hallmarking Council, guidance on fineness description, April 2014: https://assets.publishing.service.gov.uk/media/5a7f05baed915d74e6227f54/bhc-guidance-on-fineness-april-2014.pdf
  12. Hallmarking Act 1973, Schedule 1, Part II, exempt articles: https://www.legislation.gov.uk/ukpga/1973/43/schedule/1/part/II/crossheading/articles-exempt-if-of-minimum-fineness
  13. Business Companion, hallmarking quick guide: https://www.businesscompanion.info/en/quick-guides/miscellaneous/hallmarking
  14. Birmingham Assay Office, UK hallmarking requirements page: https://www.theassayoffice.co.uk/hallmarking/uk-hallmarking-requirements/
  15. Birmingham Assay Office, online dealers notice: https://www.theassayoffice.co.uk/wp-content/uploads/2026/02/online-dealers-notice.pdf
  16. London Assay Office, hallmarking guide: https://www.assayofficelondon.co.uk/media/1443/2128-hallmarking-guide-v9_july-2016.pdf
  17. London Assay Office, history of hallmarking: https://www.assayofficelondon.co.uk/about-us/history-of-hallmarking
  18. Goldsmiths' Company, history of hallmarking: https://dunstan.thegoldsmiths.co.uk/company/history/hallmarking
  19. Hallmarking Convention, how the Convention works: https://hallmarkingconvention.org/en/about-how-is-the-convention-working
  20. Swiss Federal Office for Customs and Border Security, precious metal control for watch cases: https://www.bazg.admin.ch/en/precious-metal-control-watch-cases
  21. Swiss Federal Office, official controlling and hallmarking: https://bazg.admin.ch/bazg/en/home/topics/precious-metal-control/official-controlling-and-hallmarking.html
  22. Swiss Federal Act on the Control of Trade in Precious Metals, WIPO Lex copy: https://wipolex-resources-eu-central-1-358922420655.s3.amazonaws.com/edocs/lexdocs/laws/en/ch/ch525en.pdf
  23. 16 CFR Part 23, table of contents: https://www.law.cornell.edu/cfr/text/16/part-23
  24. 16 CFR 23.2: https://www.law.cornell.edu/cfr/text/16/23.2
  25. 16 CFR 23.3, gold content and plating: https://www.law.cornell.edu/cfr/text/16/23.3
  26. 16 CFR 23.5, silver: https://www.law.cornell.edu/cfr/text/16/23.5
  27. 16 CFR 23.6, platinum group metals: https://www.law.cornell.edu/cfr/text/16/23.6
  28. 16 CFR 23.10, quality marks: https://www.law.cornell.edu/cfr/text/16/23.10
  29. ISO 9202:2019, fineness of precious metal alloys, catalogue record (iTeh Standards): ISO 9202:2019 catalogue page
  30. Grand Seiko, materials: https://grand-seiko.com/uk-en/worldofgrandseiko/manufacture/materials
  31. Plus9Time, Seiko case material codes: https://www.plus9time.com/seiko-case-codes
  32. Rolex newsroom, materials: https://newsroom.rolex.com/watchmaking/features/materials
  33. Metropolitan Museum of Art, five-piece silver tea and coffee service with iris patterns: https://www.metmuseum.org/art/collection/search/889225
  34. Wikipedia, Hallmark: https://en.wikipedia.org/wiki/Hallmark
  35. Wikipedia, Silver hallmarks: https://en.wikipedia.org/wiki/Silver_hallmarks
  36. Wikipedia, Carat (purity): https://en.wikipedia.org/wiki/Carat_(purity)
  37. Wikipedia, Gold filled: https://en.wikipedia.org/wiki/Gold_filled
  38. Wikipedia, Platinum: https://en.wikipedia.org/wiki/Platinum
  39. Wikipedia, Sterling silver: https://en.wikipedia.org/wiki/Sterling_silver
  40. Wikipedia, Palladium: https://en.wikipedia.org/wiki/Palladium
  41. Wikipedia, Gold: https://en.wikipedia.org/wiki/Gold
  42. Wikipedia, Silver: https://en.wikipedia.org/wiki/Silver
  43. Wikipedia, Titanium: https://en.wikipedia.org/wiki/Titanium
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