ISO 24016:2020 pdf free download – Jewellery and precious metals – Grading polished diamonds一 Terminology, classification and test methods.
The aim of a standard for grading unmounted polished diamonds is to set rules for determining with maximum precision and accuracy the mass, colour, clarity and cut of individual polished diamonds. On one hand, based on these four criteria – also known as “the 4C’s” – the diamond trade evaluates the value of diamonds. On the other hand, some diamond grading reports may be issued based on different standards by different laboratories, potentially leading to different results for the same individual diamond. This situation damages the reputation of the whole diamond trade. Hence, the need for a unique ISO standard for grading polished diamonds.
Today, the need for an ISO standard for the grading of polished diamonds is supported by recent agreements between international and national diamond organizations with CIBJO (The World Jewellery Confederation) with the aim of adopting CIBJO’s unique diamond grading and diamond nomenclature standard.
Together with ISO 18323, which sets the nomenclature for diamonds, synthetic diamonds and diamond simulants, an ISO standard for the grading of polished diamonds will strengthen the trust in the diamond industry worldwide.
8.3.3 Table size (percentage)
The table size shall be the average size of the table facet, expressed as a percentage of the average girdle diameter. For round stones measurements to describe the table size shall be made from opposite corner to corner and expressed as an average of the four possible measurements. For fancy shapes, table size measurements shall be taken when viewing the profile of the diamond along its length (Figures 1 and 2).
8.3.4 Crown height (percentage) and/or crown angle (degrees)
For round stones, the crown height shall be the average of eight measurements reflecting the distance from the upper girdle level to the level of the table facet, measured where the bezel/upper main facets and upper girdle level meet, and expressed as a percentage of the girdle diameter.
The crown angle shall be the average angle formed where the bezel/upper main facets and upper girdle plane meet, expressed in degrees and shall be taken by an average of all bezel facets if applicable.
For fancy shapes, the crown height and angle measurements shall be taken when viewing the profile of the diamond along its length (see Figure 1).
8.3.5 Pavilion depth (percentage) and/or pavilion angle (degrees)
For round stones, the pavilion depth shall be the average of eight measurements reflecting the distance from the lower girdle level to the level of the culet, measured where the pavilion/lower main facets meet the lower girdle level, and expressed as a percentage of the girdle diameter.
The pavilion angle shall be the average angle formed where the pavilion/lower main facets and lower girdle plane meet, expressed in degrees and shall be taken by an average of all pavilion main facets if applicable.
For fancy shapes, the pavilion depth and angle measurements shall be taken when viewing the profile of the diamond along its length.
Optionally crown height and pavilion depth can be combined to total depth and expressed as a percentage of the girdle diameter.
8.3.6 Girdle thickness (percentage) and description
The thickness of the girdle shall be the average of sixteen measurements reflecting the distance between the levels where the related lower girdle facets and upper girdle facets meet the girdle and shall be expressed as a percentage of the girdle diameter, noting the minimum and maximum and/or the average percentage.