ISO 24016 is the international standard published by the International Organization for Standardization that prescribes the requirements for the grading and disclosure of polished diamonds. Issued under ISO Technical Committee 174 (Jewellery), the standard establishes the methodology for grading natural and laboratory-grown diamonds across the four traditional Cs of colour, clarity, cut, and carat weight, together with disclosure requirements for treatments and origin. The standard is intended to harmonise diamond grading practice internationally and to support consistent retail and trade disclosure across markets.

Scope

ISO 24016 addresses the grading of polished natural diamonds in the colourless to light yellow range, equivalent to the GIA D-to-Z scale, with separate provisions for fancy-coloured diamonds and for laboratory-grown stones. The standard prescribes lighting conditions, grading magnifications, master stones for colour grading, and the descriptive scales for clarity, cut proportions, polish, and symmetry. It defines the rounding and reporting conventions for carat weight, and the supplementary descriptive elements that may appear on a grading report including measurements, fluorescence, and inscription details.

Disclosure requirements within the standard incorporate ISO 18323 by reference, requiring that natural diamonds be described as such without qualifier, that laboratory-grown stones be disclosed using the prescribed terminology (laboratory-grown, laboratory-created, or synthetic), and that any treatments be explicitly stated.

Adoption and harmonisation

ISO 24016 builds on and harmonises the prior practice of the major laboratories. GIA, IGI, HRD, the Swiss Gemmological Institute, and other major laboratories had already converged on broadly similar grading scales and methods over the prior decades. ISO 24016 provides a single international reference document for these practices, allowing national consumer-protection authorities and trade associations to point to a single standard rather than to a patchwork of laboratory-specific protocols.

National adoption has progressed at varying rates across major markets. India's BIS has been progressively aligning IS 1417 and IS 2112 with ISO 24016. The European Committee for Standardization (CEN) has incorporated the standard into European jewellery and consumer-protection frameworks. CIBJO has aligned its Diamond Blue Book with ISO 24016 in its most recent revisions.

Trade significance

For the working trade, ISO 24016 means that a diamond grading report issued by an ISO 17025-accredited laboratory operating within the ISO 24016 framework is internationally recognised as competent and can be relied upon in cross-border transactions. The standard does not displace the laboratory-specific grading reports of GIA or IGI, but provides a common reference against which they can be aligned. For consumers and retailers, ISO 24016 supports the disclosure framework set by ISO 18323 and consolidates the technical basis on which retail diamond grading is communicated.