International diamond standards explained: CIBJO, ISO, and WDC

Why standards exist: the problem they solve

Before standardised nomenclature, diamond quality claims were unverifiable. A stone described as "fine white" by one seller might be "commercial white" by another. Terms like "river white," "top wesselton," "jager," and "cape" were regional trade terms with no universal definitions. A buyer in Mumbai had no way to confirm whether a Antwerp dealer's "fine quality" matched his own understanding of that term.

International standards solve the communication problem: they define a shared vocabulary so that when a GIA certificate says "G colour, VS2 clarity," those terms mean the same thing in Mumbai, Antwerp, New York, and Tokyo. This shared vocabulary is the foundation of international diamond trade and, for consumers, the basis of the protection that certificates provide.

The five standards at a glance

The four main international diamond standards and the one in development, with their issuing bodies and key characteristics. Sources: CIBJO cibjo.org; ISO iso.org; WDC worlddiamondcouncil.org.

Section 1: CIBJO, the foundation standard

CIBJO (the World Jewellery Confederation) was founded in 1926 and is headquartered in Milan. It describes itself as the "United Nations of the jewellery business," representing national associations, trade organisations, and laboratories across the global jewellery industry (CIBJO institutional information, cibjo.org).

CIBJO's Blue Books are the primary international reference documents for jewellery industry standards. The Diamond Blue Book, current edition 2024, defines all accepted nomenclature, grading standards, and trade practices for diamonds. It covers natural diamonds, treated diamonds, laboratory-grown diamonds, synthetic diamonds, and diamond simulants. The Blue Books are living documents, updated annually, and can be downloaded free of charge from cibjo.org (CIBJO, "The Blue Books," cibjo.org/the-blue-books, 2024).

The Diamond Blue Book's most significant contribution is the standardised grading language that GIA, IGI, and other laboratories use. The D-Z colour scale, the FL-to-I3 clarity scale, and the Excellent-to-Poor cut grade terminology all align with CIBJO Blue Book definitions. When ISO developed diamond standards, it used the CIBJO Diamond Blue Book as its primary reference (CIBJO, "Industry Standards Introduction," cibjo.org/industry-standard-intro).

Read the complete CIBJO guide →

Section 2: ISO 18323:2015, consumer-facing nomenclature

Published in July 2015, ISO 18323 was the first ISO standard specifically for the diamond industry. Its primary purpose is consumer protection: it defines the permitted descriptors for describing diamonds to consumers, specifying which terms are allowed, which are misleading, and how synthetic and treated diamonds must be described (ISO 18323:2015, International Organization for Standardization, iso.org/standard/62163.html).

The most important rule in ISO 18323:2015 is definitional: the word "diamond" without further qualification always means a natural diamond. Any diamond that was grown in a laboratory must be described as a "laboratory-grown diamond," "synthetic diamond," or "laboratory-created diamond", not simply as a "diamond." This rule is now referenced in CIBJO's own standards and in the FTC guidelines in the United States.

Read the complete ISO 18323 guide →

Section 3: ISO 24016:2020, the first ISO diamond grading standard

Published in September 2020, ISO 24016 was described by CIBJO as "a historic moment for our industry, for it is the first time that a strictly defined diamond grading system has been ratified by the world's leading standards body" (CIBJO President Gaetano Cavalieri, CIBJO press release, September 2020, cibjo.org). It specifies the terminology, classification, and test methods for grading natural, unmounted, polished diamonds above 0.25 carats (ISO 24016:2020, iso.org/standard/79795.html).

ISO 24016 does not create new grading criteria, it ratifies the CIBJO Diamond Blue Book's framework as the internationally recognised standard. Laboratories that voluntarily comply with ISO 24016 can state "graded according to ISO 24016" on their reports, but must also comply with ISO 17025 (the general laboratory accreditation standard). Compliance is voluntary, GIA and IGI do not currently advertise ISO 24016 compliance on their standard reports.

Read the complete ISO 24016 guide →

Section 4: WDC System of Warranties, chain of custody

The World Diamond Council's System of Warranties (SoW) operates at a different level from grading standards, it governs the supply chain rather than the certificate. Introduced in 2002 in conjunction with the Kimberley Process, revised in 2021 with expanded scope, the SoW requires every B2B invoice for rough diamonds, polished diamonds, and diamond jewellery to include a warranty statement declaring the diamonds are conflict-free and comply with the KP (World Diamond Council, "System of Warranties," worlddiamondcouncil.org/system-of-warranties, 2024).

The current warranty statement reads: "The diamonds herein invoiced have been purchased [or sourced] from legitimate sources not involved in funding conflict, in compliance with United Nations Resolutions and corresponding national laws. The seller hereby guarantees that these diamonds are conflict free and confirms adherence to the WDC SoW Guidelines." The 2021 revision added commitments to UN human rights principles, ILO labour standards, and anti-corruption frameworks (WDC, "System of Warranties," worlddiamondcouncil.org, 2024).

Read the complete WDC System of Warranties guide →

How these standards relate to GIA and IGI certification

GIA and IGI grading reports do not typically state compliance with ISO 24016 or reference CIBJO on the certificate itself. This is because both laboratories predate these standards and operate on their own published methodologies, which in practice align closely with CIBJO Blue Book standards. The D-Z colour scale and FL-I3 clarity scale used by GIA and IGI are the same scales defined in the CIBJO Diamond Blue Book and referenced in ISO 18323 and ISO 24016. The laboratories and the standards are consistent, they were developed by the same community of gemologists, but the formal compliance relationship is not typically stated on consumer-facing certificates.

For buyers, the practical implication is: a GIA or IGI certificate uses internationally standardised terminology (aligned with CIBJO Blue Book and ISO standards) that means the same thing globally. The grade language is not arbitrary, it is the output of a framework that has been developed, debated, and ratified by the international community over decades.

What is currently in development: ISO 6893

A third ISO diamond standard is under development: ISO 6893, which will address the quality control of small diamonds (under 0.25 carats, melee) in batch form. This standard responds to the diamond watchmaking industry's need for a consistent system for assessing large parcels of small diamonds. The standard uses statistical sampling methodology (Acceptable Quality Level) to enable quality assessment of batches of 500, 2,000, or even 50,000+ small diamonds without individual stone grading (CIBJO, "New standards being developed to control quality of batches of small diamonds," cibjo.org/industry-standards-session, 2023). ISO 6893 was in development as of 2024, verify current status at iso.org.

Primary sources for this section