Overview
ISO 24016:2020 - Jewellery and precious metals - Grading polished diamonds: Terminology, classification and test methods specifies standardized terminology, classification rules and practical test methods for grading single, natural, unmounted polished diamonds over 0.25 carat. The standard covers how to describe and measure the essential quality factors of polished diamonds (colour, clarity, cut and finish), plus identification and measurement procedures. It excludes fancy-coloured, synthetic, assembled or treated diamonds except where limited treatments are explicitly allowed (see clause 7.4).
Key topics and technical requirements
ISO 24016:2020 defines procedures and requirements for:
- Scope & terminology - Standardized terms for describing polished diamonds and restrictions on allowed stone types.
- Mass and measurements - Recommended methods and instruments for determining mass (carat) and physical dimensions.
- Colour grading - Grading ranges and masterstone comparison methods (including colour scales such as D–L and M–Z ranges and handling of other hues).
- Fluorescence - Description, equipment and testing procedures for blue and non‑blue fluorescence.
- Clarity grading - Definitions of clarity grades, plotting of internal characteristics, lighting and viewing distances, and handling of features such as laser drill holes and internal graining.
- Cut & proportions - Shape identification and measurement of table size, crown height/angle, pavilion depth/angle, girdle thickness, culet size and total depth; guidance on proportion descriptions and comments.
- Finish (polish & symmetry) - Criteria and grading methods for polish and symmetry.
- Identification & testing protocols - Detailed procedures for testing mass, measurements, colour, fluorescence, clarity and proportions, plus use of masterstones and recording conventions.
Applications and who uses it
ISO 24016:2020 is intended for professionals and organizations involved in the gem and jewellery supply chain, including:
- Gemmologists and diamond grading laboratories - to ensure consistent, repeatable grading and reporting.
- Jewellery manufacturers and retailers - to describe product quality, support quality control and verify supplier claims.
- Valuers and insurers - to standardize descriptions used in appraisals and policies.
- Regulatory and trade bodies - to harmonize terminology and testing across markets.
Using ISO 24016 supports transparency, comparability of grading reports and trust in diamond transactions.
Related standards
ISO 24016 is published under ISO/TC 174 (Jewellery and precious metals). Users should consult other ISO jewellery and gem standards and national laboratory protocols for complementary guidance on synthetic diamonds, treatments and coloured stones.
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