Diamonds, Pearls and Gemstones: Japanese and Western Grading Terms, Reports and Certificates Compared

A diamond report from Tokyo, a pearl strand with a laminated certificate, a paper marked with the word kantei-sho: each speaks a slightly different dialect of the same trade. This second part of the Japonista reference sets the Japanese and Western vocabularies of diamonds, pearls, jade, coral, amber and minerals side by side, shows what each grading scale actually measures, and is candid about where laboratories, trade bodies and retailers disagree. Wherever a statement rests on a single reference, or on a retail reference rather than a laboratory or museum, the text says so.

The Japonista Curation and Concierge Team, Tokyo, Japan

The four Cs, read as a curator reads them

The vocabulary most collectors know began in California. The Gemological Institute of America created its International Diamond Grading System in 1953 and introduced the four Cs of cut, clarity, colour and carat weight as a shared framework for comparing diamonds.⁸ GIA describes the four factors as together defining a finished stone, with each factor's rarity bearing on its standing.¹ Wikipedia's survey of gemstones adds a useful caution: there is no single universal grading standard across gems, and diamonds under the GIA system made 10x magnification the norm for clarity, while many other gems are still judged largely by eye.¹⁶

Japan did not invent a rival scale for white diamonds. Japanese laboratories grade colour, clarity, cut and carat against internationally recognised scales, and Central Gem Laboratory in Tokyo says its diamond reports are accepted by major Japanese jewellery retailers and department-store counters.¹³ What differs is the surrounding paper culture: the names of documents, the role of the appraiser, the weight placed on a certificate, and the way pearls, jade and coral are described. That is the territory this guide maps.

Colour: the D to Z ladder

GIA grades white diamonds from D, colourless, to Z, pale yellow or brown. The letters A to C are skipped to avoid confusion with older terms. A grader compares the unset stone with master stones, table down, under daylight-equivalent light; a mounted stone receives only an estimated range.⁵ A Japanese retail guide describes the same scale as twenty-three steps from D down to Z, with lower grades tending to look more yellow.¹⁴ GIA also notes that faint blue fluorescence can offset a slight yellow tint, while strong fluorescence can make a stone look hazy.¹

Figure 1. The GIA colour ladder with the five descriptive anchors given in the reference.⁵

Other colour vocabularies exist, and the same reference lists them: the American Gem Society uses a numeric scale from 0 to 10 tied to colorimeter readings, CIBJO uses descriptive terms from exceptional white through slightly tinted and tinted, and the Scandinavian nomenclature uses two numbered series. Older trade names such as River, Top Wesselton and Cape were never standardised.⁵ A collector who meets an unfamiliar term on an older certificate should therefore ask which scale was in use, not assume a letter equivalent.

Clarity: eleven grades and their cousins

GIA's clarity scale has eleven grades in six categories: Flawless, Internally Flawless, two grades each of very, very slightly included, very slightly included and slightly included, and three included grades. Stones are examined at 10x magnification, and graders weigh the size, nature, position, relief and number of the marks.²¹

Figure 2. GIA clarity ladder, with the label sets of other laboratories noted but not aligned.⁴²

The comparison matters for a practical reason. The reference notes that GIA and the American Gem Society rely on stereo microscopes with darkfield lighting, while CIBJO and some other bodies specify a 10x loupe in normal light, and that the same label does not always mean the same thing from one laboratory to the next.⁴ The Jewellers Association of Australia once warned that some certificates overstate colour and clarity by more than one grade, and that a certificate offers no protection if it is wrong, while stressing that most GIA certificates are correct.¹⁵

Grading scale equivalents: what each laboratory family uses
Factor	GIA	AGS	CIBJO family	Reading note
Colour	D to Z letters	Numeric 0 to 10	Descriptive white and tinted terms	No official letter equivalent for CIBJO terms
Clarity	FL to I3, eleven grades	Numeric 0 to 10	Loupe Clean, VVS, VS, SI, P1 to P3	Different method: microscope versus loupe
Cut (round brilliant)	Excellent, Very Good, Good, Fair, Poor	0 Ideal to 10 Poor	Varies by body	GIA cut grade on reports since 2006
Carat	Metric carat	Metric carat	Metric carat	200 milligrams, in force since 1907

Table drawn from the references on colour, clarity, cut and carat cited in this part.⁴⁵⁶⁷

Cut and carat

Cut is the factor that most resists a single number. Since 2006 GIA has graded the cut of round brilliants on five levels, from Excellent to Poor, while the American Gem Society's 2005 standard scores cut from 0 to 10, with 0 labelled Ideal.⁶ The benchmarks beneath these grades differ by tradition: the American Standard of 1919, the German Practical Fine Cut of 1939 and the Scandinavian Standard of 1969 each set slightly different table sizes and crown angles, while the pavilion angle varies least because it is tied to total internal reflection.⁶ Carat is the simplest factor. The metric carat is 200 milligrams, divided into 100 points of 2 milligrams each, and an international conference in Paris adopted it in 1907; before that, national carats ranged from about 187 to nearly 216 milligrams.⁷

Figure 3. Parts of a round brilliant, the GIA and AGS cut scales, and the metric carat.⁶⁷

Japanese laboratories and report practice

Central Gem Laboratory, founded in Tokyo in 1970 in the Taito ward, was set up to bring standards to a trade that lacked clear identification and appraisal methods; its core services are gem identification, diamond grading, appraisal and training.¹⁰ It took part in CIBJO as technical adviser to the Japan Jewellery Association from 2004, joined the CIBJO Colored Stone Steering Committee in 2006, and announced its participation in the Laboratory Manual Harmonisation Committee in 2011.¹⁰ The same history records the Association of Gemmological Laboratories, Japan, formed in 1981 by the country's identification bodies.¹⁰ Wikipedia's gemstone article lists GAAJ-ZENHOKYO in Tokyo among seven major laboratories that formed a committee to standardise report wording and methods.¹⁶ Nothing further is claimed here about its report formats.

CGL issues two kinds of report. A gem identification report covers all gems and states what the stone is and whether it is an imitation; a diamond grading report covers diamonds only and assesses them on the four Cs. Neither report states a monetary figure.⁹ Its international report includes a photograph and follows LMHC standards, not necessarily the Japanese AGL standards.¹² A retail reference page adds that reports are issued in Japanese and English, and that even harmonised laboratories can differ on borderline stones, particularly origin, so a second report from another LMHC member is advisable for important stones.¹³ That page is a retailer's encyclopaedia and is treated here as supporting, not primary, evidence.

The laboratory's own terms are the most instructive document. They say a report neither guarantees nor states an appraisal value, applies to the single item examined, may be reissued only within two years, and becomes invalid if the item is altered or its shape or quality changes. In the terms' own words, a report "shall not be used or presented as a certificate for assessing value."¹¹

Terminology map: Japan and the West

Romanised Japanese terms in this guide are given in italics. The map below pairs each with its nearest Western term and states, from the references, where the pairing is loose.

Figure 4. Six romanised Japanese terms and the Western terms that sit closest to them.⁴⁵³⁶²⁰²⁵

Terminology, Japan versus West
Romanised term	Plain meaning	Western counterpart	Caveat
kantei-sho	Document by a qualified expert certifying value, authenticity or quality	Appraisal certificate or grading report	A Japanese retail guide uses it and the English grading report for the same diamond document; elsewhere it can imply a stated value⁴⁵¹⁴
kanbetsu-sho	Certifies what an item is, not its grade or value	Identification report	Closest to the CGL gem identification report⁴⁵⁹
hisui	Translucent gem-quality jadeite rock with over 90 per cent jadeite	Jadeite jade	Nephrite is another jade but is not hisui³⁶
aka	Dark red precious coral, often with a pale core	Corallium japonicum; trade names Moro and Oxblood	Trade names are not always species names²⁰
momo	Bright red to salmon or flesh-toned coral	Pleurocorallium elatius; trade names Satsuma, Cerasuolo	Light pink variants appear as Angel skin, Boke or Magai²⁰
shiro	White coral	Pleurocorallium konojoi; Pure White	Colour name as well as species name²⁰
hanadama	Flower pearl; top Akoya tier	None official; vendor AAA is a different idea	Certification by one private laboratory, applied only to the tested strand²⁵

One caution on omissions. Several Japanese trade phrases for diamond colour and clarity circulate in retail writing, but none is defined in the references cited here in a way that can be checked, so they are left out rather than guessed.

Anatomy of a report and an appraisal certificate

A diamond grading report in the GIA and CGL manner lists items such as date, report number, shape, measurements, carat, colour, clarity, cut, fluorescence, proportions and a plot of the inclusions.¹⁴ A CGL identification report states the mineral type, whether the stone is natural, synthetic or an imitation, and any treatment found.¹¹ A kantei-sho in the wider Japanese sense is a document from a qualified appraiser, and a cognate record, kanbetsu-sho, says what an item is but not what it is worth.⁴⁵

Figure 5. Fields on a grading report and the statements made by Japanese appraisal and identification papers.¹⁴¹¹⁴⁵

Pearls: Akoya, Mikimoto and the letter grades

Akoya pearls come from the small pearl oyster Pinctada fucata, which grows only some six to eight centimetres, a limit that explains why Akoya over ten millimetres are scarce.³⁰ The history is contested in detail. Kokichi Mikimoto produced hemispherical cultured pearls in 1893 and received patents in 1896 and 1908; the 1916 patent covered round pearls in mantle tissue, and after 1916 he adopted methods developed by Tokichi Nishikawa and Tatsuhei Mise.³¹ Sotheby's dates fully round production to about a decade after 1893, and a Japanese news feature places the round-pearl patent in 1916, so a careful writer gives a range rather than one year.³²³³ In 1935 Mikimoto publicly burned large quantities of poor pearls to protect the name of his cultured pearls, and the island at Toba where he worked became Mikimoto Pearl Island in 1951.³¹³⁴

GIA assesses pearls on seven factors: size, shape, colour, lustre, surface quality, nacre quality and matching. It presents lustre as possibly the most important, and its only graded scale is descriptive, running from Excellent to Poor for lustre, with no letter grades.³ CIBJO's Pearl Book supplies shared vocabulary for lustre, surface, shape, colour and nacre without requiring one universal scale, and requires treatments such as bleaching, dyeing and coating to be disclosed, according to a retail reference summarising it.²² By contrast, the familiar triple A is a commercial convention. One vendor page states plainly that each vendor grades AAA on its own scale, so grades cannot easily be compared across houses.²⁶ Another describes AAA as mirror-like lustre with a surface about 95 per cent clean, and AA as about 85 per cent, and advises collectors to look for published criteria.²⁷

Mikimoto's own scale, as shown in a retailer's reproduction of the house card, has four tiers: AAA, AA, A+ and A, distinguished by lustre and the marks on the surface.²⁹ A second retailer repeats the four tiers and adds that the house selects only about five per cent of the pearls it inspects, a figure from one retail page that the house itself does not state.²⁸

Figure 6. Three ways of describing Akoya quality: a house scale, an instrument-tested certification and a descriptive laboratory scale.²⁹²⁶³

Pearl grading: Japan versus West
System	Form	Who issues it	What it tells you	What it does not
Vendor AAA	Letters	Each house	The house's own view of lustre, surface and shape	Comparability between houses²⁶
Mikimoto tiers	AAA, AA, A+, A	The house	Lustre and surface on a four-step scale	An independent opinion²⁹
Hanadama	Certificate, fixed lengths	Pearl Science Laboratory, Tokyo	Measured nacre, lustre, surface and interference colour	Anything about other strands, or non-Akoya pearls²⁵²⁶
GIA factors	Descriptive	GIA	Seven value factors; lustre from Excellent to Poor	A single overall letter grade³
CIBJO Pearl Book	Shared vocabulary	Trade confederation	Names, treatment disclosure, quality terms	One universal scale²²

Nacre thickness is where retail references drift apart. One reference gives a CIBJO recommended minimum for Akoya of 0.35 millimetres and notes that Japan's domestic export inspection required between 0.3 and 0.4 at different times, with the mandatory programme relaxed in the 1990s.²³ Hanadama tests ask for at least 0.40 millimetres per side.²⁶ The Hanadama term itself has sometimes been used in retail without a certificate, so the certificate, not the word, is the evidence.²⁵

Collectors browsing pearl pieces at Japonista can find them in the Pearls collection, and fine houses in the Fine Jewellery Houses collection.

Jade, coral and amber

Jade. In Japanese gemmology, hisui means translucent gem-quality jadeite rock with more than 90 per cent jadeite; nephrite does not qualify. Japan has ten known jadeite localities, and Itoigawa in Niigata Prefecture is the most famous and the home of high-quality gem jadeite. Jadeite use there dates back about five thousand years, according to a paper by the National Museum of Nature and Science.³⁶ The Itoigawa Geopark states that jade is both Niigata's prefectural stone and carries a national stone designation, and that Itoigawa's deposits are the only ones in Northeast Asia to yield gemstone-quality jade.³⁷ On treatment, Wikipedia notes that since the late twentieth century natural jadeite has been bleached and impregnated with polymer to improve colour or translucency, which standard gemmological testing can detect.³⁵ The letter system of Type A, B and C jade is not defined in the references cited here, so it is not described.

Coral. CIBJO's coral guide reserves precious coral for red, pink and white species of the family Corallidae in three genera, and sets bamboo, black, sponge, golden and blue corals apart as other categories.²⁰ It also states that common corals are often bleached, dyed or impregnated to imitate precious coral, and refers readers to the Coral Book for disclosure rules.²⁰ The 2023 Coral Commission report adds that Japan is a place of origin for precious coral in the CITES discussion, and that cleaning coral during fashioning removes living tissue, which makes living and non-living material practically impossible to tell apart.²¹

Amber. A 2025 classification chart prepared under CIBJO and LMHC standards records that Baltic amber can be dyed, clarified, aged or heated, and that heated amber cannot be called natural. Pressed amber, made by fusing fragments at roughly 120 to 180 degrees Celsius, is regarded by many specialists as an imitation.⁴⁴ GIA's gem news on root amber shows how laboratories separate natural, reconstructed and plastic material: microscopy distinguishes natural from reconstructed, and infrared spectroscopy is the fastest route to spotting plastic.⁴³

Treatment disclosure compared

Disclosure is where trade practice is least uniform. The CIBJO Blue Books, comprising Gemstone, Diamond, Pearl, Precious Metals, Gemmological Laboratory and, since 2015, Coral, are voluntary reference standards reviewed yearly and are among the most widely accepted benchmarks in a trade where few standards carry ISO endorsement.¹⁹ Wikipedia's gemstone article warns that laboratories do not always agree: one may call a stone untreated where another reports heat treatment.¹⁶

Treatment disclosure, by material
Material	Common treatments	Disclosure position in the references	Japan note
Diamond	Fracture filling, laser work	Fracture filling noted for diamonds in general¹⁶	CGL reports note treatments found¹¹
Pearl	Bleaching, dyeing, coating, irradiation	To be disclosed under the Pearl Book summary²²	Hanadama certification covers Akoya only²⁵
Jadeite	Bleaching, polymer impregnation	Detectable by standard testing³⁵	Hisui is defined by rock composition, not treatment status³⁶
Coral	Bleaching, dyeing, resin on common coral	Detail left to the Coral Book²⁰	Aka, momo, shiro are trade colour and species names²⁰
Amber	Dyeing, clarifying, ageing, heating, pressing	Heated amber is not natural; pressed is imitation to many specialists⁴⁴	No Japan-specific rule found
Tourmaline	Heat, irradiation, clarity enhancement	Irradiation nearly undetectable; enhanced paraiba is worth much less⁴²	No Japan-specific rule found

Lab-grown stones

Lab-grown diamonds share the chemical and physical properties of mined stones, and laboratories separate them with spectroscopy and ultraviolet fluorescence instruments. Major laboratories laser-inscribe the girdle of each lab-grown diamond they certify with the report number and a lab-grown notice, readable at 10x.¹⁷ In 2018 the United States Federal Trade Commission revised its Jewelry Guides to remove the word natural from the definition of diamond, and GIA dropped the word synthetic from its lab-grown reports in July 2019.¹⁸ Undisclosed lab-grown melee, the small accent stones, has appeared in trade parcels since 2013, partly because some dealers do not test them.¹⁷ CGL's reports state whether a stone is natural, synthetic or an imitation.¹¹ The references cited here set out no Japanese statutory disclosure rule for lab-grown stones, so none is claimed.

Birthstones in Japan and the West

Birthstone lists are cultural agreements, not mineral facts. The first American list was standardised in 1912, with revisions in 1952, 2002 and later; one historian is quoted as calling the 1912 list a marketing exercise without solid historical basis.³⁸ Britain's National Association of Goldsmiths issued its own list in 1937 with differences in several months.³⁸ The Yamanashi Jewelry Museum records that Japan's list was first set in 1958 on the basis of a United States guild list, with jade and coral added; in December 2021 it was revised for the first time in sixty-three years, adding ten stones for a total of twenty-nine, led by the National Jewelry Wholesalers Association with the Japan Jewelry Association and the Yamanashi Crystal Jewelry Cooperative Association.⁴⁰

Birthstone lists: milestones compared
Tradition	First standard list	Later changes recorded	Distinctive note
United States	1912	1952 added alexandrite, citrine, tourmaline and zircon; tanzanite 2002; spinel later³⁹	Trade bodies still differ on moonstone and bloodstone³⁹
United Kingdom	1937	2013 column differs in several months³⁸	Bloodstone for March; citrine alone for November in one summary⁴¹
Japan	1958	Revised December 2021, ten stones added, total twenty-nine⁴⁰	Jade and coral included⁴⁰
Hindu tradition	Not month based	Nine celestial bodies, the Navaratna³⁸	Stones suited to the individual by astrology³⁸

The ten stones added in 2021 are not named in the references cited here, so they are not listed.

Tourmaline and mineral names

Tourmaline shows how trade names stack on mineral names. Rubellite is the red to pinkish-red variety of the lithium-rich species elbaite, indicolite the light blue to bluish-green variety, and verdelite the green. Paraiba-type tourmaline is copper-coloured blue or green, with material found in Brazil, Nigeria and Mozambique, and a non-magnetic blue stone points to copper colouring while a magnetic one is coloured by iron.⁴² The same page records heat treatment to lighten dark red stones and irradiation to intensify pink, and warns that clarity-enhanced paraiba is worth much less than untreated material.⁴² Japan's mineral heritage is told through its museums as well: the National Museum of Nature and Science notes three new minerals first found in Itoigawa jadeitite, itoigawaite, rengeite and matsubaraite.³⁶

Watches, metal marks and serial systems

Metal marks. The Japan Jewellery Association's metal guide states that each item should show its main precious metal and fineness in parts per thousand, such as Au750, and that the standard form of karat notation puts the K before the number, so K18 equals 750. Platinum of 900 parts per thousand is Pt900, an item below 850 parts cannot be called platinum jewellery, and fineness grades follow JIS H6309:2022. Gold and platinum bearing a Mint certification stamp may omit the metal and fineness, and antique pieces may carry no fineness mark at all.⁴⁷ A mark therefore records a claim about alloy, and the guide's own exemptions show where a mark can be absent without implying anything wrong.

Watches. Grand Seiko's warranty registration page shows how a Japanese maker ties paper to object: the model and serial numbers are found on the case back, and for limited editions only the figure before the slash is entered, so that 8 identifies 8 of 100.⁴⁶ The page does not explain a reference number separately, and it does not describe any anti-counterfeit feature, so none is claimed. The same logic of a unique number joined to a document appears in the Hanadama certificate, which retail pages describe as laminated, serial numbered and watermarked,²⁶ and in the laser inscription on lab-grown diamonds.¹⁷ Collectors who wish to see Japanese horology can browse Japanese Horology and Collectible Watches, and Japanese gold in the Japan Gold collection.

Provenance: what papers prove and what they do not

A certificate is evidence about a stone at one moment, written by one organisation. It is not a passport. The table below separates what each common document supports from what it leaves open.

Provenance: proof and its limits
Document or mark	What it supports	What it does not prove
Laboratory grading report	The grades and measurements of the stone examined, on the date given¹⁴	A value; agreement with another laboratory; that the report still matches a stone that has been recut or changed¹¹
Identification report (kanbetsu-sho)	What the item is, including natural, synthetic or imitation⁴⁵¹¹	Grade or value⁴⁵
Appraisal certificate (kantei-sho)	An expert's opinion of value, authenticity or quality⁴⁵	That another appraiser would say the same; that the opinion is current
Hanadama certificate	Instrument-verified measurements on the tested strand²⁵	Quality of any other strand; a universal industry standard²⁵
House grade such as Mikimoto A+	The house's own assessment²⁹	An independent grade comparable with other houses²⁶
Metal fineness mark	A declared alloy content in parts per thousand⁴⁷	Age, maker or plating history; some genuine pieces carry no mark⁴⁷
Warranty card and serial number	That a number was registered to a model⁴⁶	That the watch and card were never separated or the movement never changed
Museum record	That the institution holds and describes a comparable object⁴⁹	That a private piece shares its history

The laboratories are candid about this themselves. CGL's terms, quoted above, rule out use of a report as a valuation, and its history page presents the laboratory as a promoter of standards, not an insurer of outcomes.¹¹¹⁰ The Australian warning about overgraded certificates carries the same lesson: a certificate cannot protect against its own error.¹⁵

Where the records disagree

Clarity labels. GIA and the American Gem Society use microscopes with darkfield lighting; CIBJO, the World Jewellery Confederation and IDC use a loupe in normal light, and EGL adds an SI3 grade that other laboratories do not use.⁴
Colour vocabularies. Letters, numbers, descriptive words and older trade names coexist, and the older names were never standardised.⁵
Cut benchmarks. The American, Scandinavian and German standards set different table and crown values.⁶
Origin and treatment findings. Laboratories can differ on borderline stones, and the references say plainly that origin is the hardest question.¹⁶¹³
Pearl grades. Mikimoto uses four tiers, other vendors use AAA to A on their own terms, and GIA uses no letters.²⁹²⁷³
Nacre minimums. 0.35 millimetres for the CIBJO recommendation, 0.3 to 0.4 for Japan's historic export inspection, 0.40 per side for Hanadama.²³²⁶
Round pearl dates. Mikimoto's hemispherical pearls of 1893, round pearls about a decade later in one account and a patent in 1916 in others.³¹³²³³
Birthstones. Japan's 1958 list and 2021 revision, the 1912 and 1952 American lists and the 1937 British list all differ.³⁸⁴⁰
Pressed amber. Labelled treated by some and imitation by many specialists.⁴⁴
Founding of GIA. The references give both the 1920s and 1931.⁸

The consistent advice is practical: for an important stone, seek reports from more than one harmonised laboratory, and read each report's date and terms.¹³

See the evidence

This strip links to reference pages. No photographs are embedded or copied. Credit and licence lines are quoted as shown on each page. Readers who wish to see photographs of stones and certificates are invited to search Wikimedia Commons directly.

Tokyo National Museum, comma-shaped bead (magatama) with smaller beads. Talc, sixth century. Licence line shown: Attribution (CC BY 4.0).⁴⁹
Smithsonian record for the Hope Diamond. Describes a 45.52 carat blue diamond. Credit line: none shown; rights fields state both no restrictions and that usage conditions apply, so check the museum's terms before any reuse.⁴⁸
Mikimoto Pearl Island, Wikipedia article. Describes the island, museum and ama diver displays.³⁴
National Museum of Nature and Science, paper on its jadeite exhibition and collection. Reports roughly 200 jadeite-bearing rock specimens and 109 jadeite mineral specimens.³⁶

Questions readers ask

Is a Japanese diamond report weaker than a GIA report?

The references do not rank them. CGL reports use internationally recognised scales and the laboratory participates in the Laboratory Manual Harmonisation Committee, but laboratories, including harmonised ones, can differ on borderline stones.¹³ The honest answer is that the reports are different opinions from different laboratories, not interchangeable ones.

What does kantei-sho mean on a Japanese certificate?

It is a document by a qualified expert certifying value, authenticity or quality.⁴⁵ It is not a laboratory grade in the GIA sense, and it should be read together with the issuer's name and date.

Is hanadama an official grade?

It is a certification from a single private laboratory, the Pearl Science Laboratory in Tokyo, with instrument-verified criteria. It is not described as a government or universal standard, and it applies only to the tested Akoya strand.²⁵

Does triple A mean the same everywhere?

No. Vendors grade AAA on their own scales, and Mikimoto's house scale is a separate four-tier system.²⁶²⁹

Are momo and aka different stones?

They are different species and colour families of precious coral. Aka is Corallium japonicum, dark red, while momo is Pleurocorallium elatius, ranging from red to salmon.²⁰

Does a certificate protect me if the grade is wrong?

Not by itself. The Australian jewellers' warning said a certificate offers no protection if it is wrong, and CGL's terms cap its liability and rule out use of a report as a valuation.¹⁵¹¹

Is lab-grown diamond treated or simply different?

It is the same pure carbon crystal as a mined diamond but made by a controlled process, and it is identified, not graded as treated. Certifying laboratories inscribe the girdle to say so.¹⁷

Why do birthstone lists differ between Japan and the West?

Each trade body set its own list: the United States in 1912, Britain in 1937 and Japan in 1958, with Japan revising its list in 2021.³⁸⁴⁰

This is the second part of our reference. Part one covers metal purity marks, hallmarks and watch case metals.

References

The pages below are the references cited in this part. Retail pages are marked as such and are treated as supporting evidence only.

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