The CIBJO Diamond Book is the volume within the CIBJO Blue Book series that establishes internationally recognised standards for the nomenclature, grading, and disclosure of diamonds in the jewellery trade. Published by CIBJO — the World Jewellery Confederation (Confédération Internationale de la Bijouterie, Joaillerie, Orfèvrerie des Diamants, Perles et Pierres) — the Diamond Book serves as a reference framework for trade associations, grading laboratories, retailers, and regulators across member nations. Its authority derives not from legal mandate in most jurisdictions but from broad voluntary adoption: compliance is required or strongly encouraged by many national trade bodies, and its definitions underpin the terminology used by major grading laboratories including GIA, HRD Antwerp, and IGI.

Purpose and Scope

The Diamond Book addresses the full commercial lifecycle of a diamond as it moves from mine to market. Its central function is to define, with precision, the vocabulary that the trade uses to describe diamonds — ensuring that a term such as "natural diamond" or "treated diamond" carries the same meaning in Tokyo, Antwerp, Mumbai, and New York. Without such harmonisation, the same stone could be described in conflicting terms by different parties in a single transaction, creating the conditions for inadvertent or deliberate misrepresentation.

The document is structured around several core concerns: the classification of diamond types, the standardisation of grading parameters, the identification and mandatory disclosure of treatments, and the guidelines governing the issuance of diamond grading reports. Each of these areas is addressed with enough specificity to be operationally useful while remaining flexible enough to accommodate the practices of different laboratory systems.

Classification of Diamond Types

One of the Diamond Book's most consequential contributions is its clear taxonomy of diamond types, which has become foundational to trade disclosure practice globally. The principal categories are:

• Natural diamond: A diamond formed by geological processes in the earth, without human intervention in its creation. This is the baseline category against which all others are defined.
• Synthetic diamond (laboratory-grown diamond): A diamond produced by human-controlled processes — principally High Pressure High Temperature (HPHT) synthesis or Chemical Vapour Deposition (CVD) — that replicates the crystal structure, chemical composition, and physical properties of a natural diamond. The Diamond Book requires that synthetic diamonds be unambiguously identified as such at every point of sale, and that terms such as "cultured diamond" or "created diamond" not be used in ways that obscure the synthetic origin.
• Treated diamond: A natural or synthetic diamond that has been subjected to post-growth or post-mining processes designed to alter its appearance. The Diamond Book specifies which treatments require disclosure and the language in which that disclosure must be made.

This tripartite structure reflects the trade's need to protect consumers from confusion between categories that, while chemically identical, differ fundamentally in origin, rarity, and — in the case of natural versus synthetic — market value.

The 4Cs Framework

The Diamond Book codifies the internationally accepted grading system based on the four principal quality parameters: colour, clarity, cut, and carat weight — collectively known as the 4Cs. While the 4Cs framework was developed and popularised by GIA in the mid-twentieth century, the Diamond Book's role is to establish internationally agreed definitions and scales that allow grading reports issued by different laboratories to be understood within a common framework.

• Colour: The Diamond Book endorses a grading scale for colourless-to-light-yellow diamonds running from D (colourless) through Z, consistent with the GIA scale that has become the global standard. For fancy-colour diamonds, it provides guidance on the use of hue, tone, and saturation descriptors.
• Clarity: Clarity grades are defined in relation to the visibility of internal characteristics (inclusions) and surface features (blemishes) under 10× magnification. The scale runs from Flawless through Internally Flawless, Very Very Slightly Included (VVS1/VVS2), Very Slightly Included (VS1/VS2), Slightly Included (SI1/SI2), and Included (I1/I2/I3).
• Cut: The Diamond Book addresses cut in terms of proportions, symmetry, and polish, acknowledging that cut quality directly affects a diamond's optical performance. It provides guidance on acceptable terminology for cut grades and cautions against the use of superlative or proprietary terms that cannot be independently verified.
• Carat weight: Defined as the metric carat (0.200 grams), with requirements for accuracy of measurement and rounding conventions on grading reports.

Treatment Disclosure Requirements

The disclosure of treatments is arguably the area in which the Diamond Book has its greatest practical impact on consumer protection. The document identifies the principal treatments applied to diamonds and establishes that each must be disclosed at every stage of the commercial chain, from manufacturer to end consumer. The treatments addressed include:

• HPHT annealing: High Pressure High Temperature treatment applied to natural diamonds to remove or alter colour, producing colourless or fancy-colour stones from otherwise less desirable material. HPHT-treated diamonds must be disclosed as such, and the treatment is generally detectable by specialist gemological laboratories.
• Irradiation and annealing: Exposure to radiation (and subsequent heat treatment) to induce fancy colours — greens, blues, yellows, and pinks — in otherwise low-value material. The Diamond Book requires full disclosure, as irradiation-induced colour is not equivalent in origin or stability to natural colour.
• Laser drilling: A technique in which a laser is used to create a narrow channel to a dark inclusion, which is then dissolved with acid to improve clarity appearance. The Diamond Book requires disclosure because laser drilling permanently alters the stone's structure.
• Fracture filling (clarity enhancement): The injection of a glass-like substance into surface-reaching fractures to reduce their visibility. This treatment is less stable than laser drilling and requires explicit disclosure, as it can be damaged by heat and certain cleaning methods.
• Coating: The application of a thin surface layer to alter colour or surface appearance. Coating is considered a non-permanent treatment and requires the most explicit disclosure, as it can be removed by routine wear or cleaning.

The Diamond Book's position is that no treatment may be concealed or minimised in trade communications, and that grading reports must clearly state the presence of any detected treatment. Laboratories that comply with CIBJO standards are expected to use standardised language on their reports rather than proprietary euphemisms that might obscure the nature of the treatment from a non-specialist buyer.

Grading Reports and Laboratory Standards

The Diamond Book provides guidelines for the content and presentation of diamond grading reports, specifying the minimum information that a compliant report should contain: the diamond's weight, measurements, shape and cutting style, colour grade, clarity grade, cut grade (for round brilliants), and a disclosure of any detected treatments or synthetic origin. It also addresses the language used to describe fancy-colour diamonds and the conventions for plotting inclusions on clarity diagrams.

While the Diamond Book does not accredit specific laboratories, its standards inform the practices of the major international grading institutions. GIA, HRD Antwerp, and IGI have each developed their own methodologies and scales, but these are broadly consistent with CIBJO's framework, enabling reports from different laboratories to be compared with reasonable confidence by informed trade professionals.

Periodic Revision and Emerging Challenges

The Diamond Book is a living document, revised periodically by CIBJO's Diamond Commission to address developments in diamond production, treatment technology, and detection science. The rapid growth of the laboratory-grown diamond sector since the mid-2010s prompted significant revisions to the nomenclature sections, particularly regarding the terminology permissible for synthetic diamonds and the disclosure obligations of retailers selling laboratory-grown stones alongside natural diamonds. The Diamond Book now takes a clear position that laboratory-grown diamonds must be identified as such and that their synthetic origin must be disclosed in all trade communications, including advertising.

The increasing sophistication of HPHT and CVD synthesis — producing stones that are increasingly difficult to distinguish from natural diamonds by conventional gemological testing — has also driven updates to the sections on detection and laboratory referral. The Diamond Book encourages the use of specialist detection instruments and, where necessary, referral to a gemological laboratory equipped with advanced spectroscopic equipment, when the natural or synthetic origin of a stone cannot be confirmed by standard testing.

Significance in the International Trade

The Diamond Book occupies a central position in the architecture of international diamond trade standards, alongside documents such as the Kimberley Process Certification Scheme (which addresses conflict diamonds) and the grading standards of individual laboratories. Its value lies in providing a common language that transcends national boundaries and laboratory affiliations — a shared vocabulary that allows a diamond described in one country to be understood with confidence in another. For trade associations, retailers, and laboratories seeking to demonstrate their commitment to transparency and consumer protection, compliance with the Diamond Book represents a recognised benchmark of professional conduct.

Further Reading

• CIBJO Blue Book series — cibjo.org
• GIA: The 4Cs of Diamond Quality — gia.edu
• GIA: Laboratory-Grown Diamonds — Gems & Gemology