This standard specifies terms and definitions, diamond grading principles by color, clarity and cuts, diamond quality and diamond grading certificate for natural loose and set polished diamonds.
This standard is applicable to diamond grading and related activities in the fields of jewelry and gem testing, antique authentication, commerce and trade, customs, insurance, pawning, asset evaluation, scientific research and teaching, and literature publishing.
The color grading of this standard is applicable to loose and set polished diamonds from colorless to light yellow (brown and gray).
The cut grading of this standard is applicable to loose and set polished diamonds of round brilliant cut.
The grading principles in this standard are applicable to loose and set polished diamonds without optimization treatment such as film covering and crack filling.
The grading principles of this standard are applicable to loose polished diamonds with a weight greater than or equal to 0.040 0 g (0.20 ct) and set polished diamonds with a weight between 0.040 0 g (0.20 ct, inclusive) and 0.200 0 g (1.00 ct, inclusive). For loose and set polished diamonds with a weight less than 0.040 0 g (0.20 ct) and set polished diamonds with a weight larger than 0.200 0 g (1.00 ct), this standard may apply.
For loose and set polished diamonds other than those from colorless to light yellow (brown and gray), the clarity grading may comply with this standard; the cut grading of round brilliant cut may comply with this standard.
For loose and set polished diamonds other than round brilliant cuts, the color grading, the clarity grading, and the finish (polish and symmetry) grading under cut grading may comply with this standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
For the purposes of this document, the terms and definitions given in GB/T 16552 and GB/T 16553, and as follows apply.
3.1
diamond
equiaxed crystal natural mineral composed of carbon atoms, with a mohs hardness of 10, a density of 3.52 (± 0.01) g/cm3, a refractivity of 2.417, and a dispersion of 0.044
3.2
diamond grading
grading of diamond by the four Cs—Color, Clarity, Cut and Carat weight
3.3
color grading
grading of diamond color made by colorimetry under the specified environment
3.3.1
diamond master-stone set
one set of round brilliant cut diamond samples with calibrated color grades, which in turn represent successive color levels from high to low, and can be traced to the standard samples of the origin country of the master-stone set. The grades defined in diamond master-stone set represent the lower limit of the color grade.
3.3.2
diamond light
fluorescent lamp with a color temperature ranging from 5 500 K to 7 200 K
3.3.3
white background
white plate or white paper with no fluorescence and no obvious directional reflection, used as colorimetry background
3.3.4
fluorescence degree
the intensity of visible light emitted by a diamond under long-wave UV light
3.3.5
master-stone of fluorescence degree
one set of round brilliant cut diamond samples with calibrated fluorescence degrees, consisting of 3 pieces, which in turn represent the lower limits of the grades of strong, medium and faint
3.4
clarity grading
grading of diamond internal and external characteristics, under 10x magnification
3.4.1
internal characteristics
natural inclusions, birthmarks and man-made characteristics contained in or extended into a diamond (see Table A.1 of Annex A)
GB/T 16554-2017 The following standards are cited：
