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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 16554-2010 Diamond grading.
Main changes have been made as follows with respect to GB/T 16554-2010:
—The definitions of some terms, such as table percentage, crown height percentage and overweight percentage, have been modified (see 3.5.16.1~3.5.16.8 and 3.5.16.10; 3.5.16.1~3.5.16.8 and 3.5.17.6 of 2010 edition);
—The terms and definitions of out-of-round, table off-center, culet off-center, table/culet alignment, crown height variation, crown angle variation, pavilion depth variation, pavilion angle variation, girdle thickness variation and table size variation have been introduced (see 3.5.17.1. 1 ~ 3.5.17.1.10);
—The term and definition of “l(fā)izards skin” effect has been removed (see 3.5.17.7 of 2010 edition);
—Fluorescence color has been introduced (see 4.2.3);
—The determination principle of SI2 clarity grade has been modified (see 5.2.4; 5.2.4.2 of 2010 edition);
—Measurement of symmetry has been introduced (see 6.1.5);
—The determination principle of overweight grade has been modified (see 6.2.3.1.2; 6.2.3.1.2 of 2010 edition);
—The symmetry grading has been modified (see 6.3.2; 6.3.1 of 2010 edition);
—The measurement of weight has been modified (see 7.2; 7.2 of 2010 edition);
—Chip, etch channel, knot and twinning wisp have been introduced to Table A.1 of Annex A and the description of cavity has been modified (see Annex A);
—Dop burn and lizards skin have been introduced to Table A.2 of Annex A and the description of burn mark has been modified (see Annex A);
—Some parameters in pavilion depth percentage of Tables C.5 ~ C.14 of Annex C have been modified (see Annex C);
—Suggested carat weights for average diameters from 9.5 mm ~ 11.0 mm have been introduced to Table D.1 of Annex D (see Table D.1 of Annex D).
Attention is drawn to the possibility that some of the elements of this standard may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This standard was proposed by the Ministry of Land and Resources.
This standard is under the jurisdiction of the National Technical Committee on Jewelry and Jade of Standardization Administration of China (SAC/TC 298).
The previous editions of the standard replaced by this standard are as follows:
—GB/T 16554-1996, GB/T 16554-2003 and GB/T 16554-2010.
Diamond grading
1 Scope
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.
GB/T 16552 Gems—Nomenclature
GB/T 16553 Gems—Testing
3 Terms and definitions
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)
3.4.2
external characteristics
natural birthmarks and man-made characteristics present only on external surfaces of a diamond (see Table A.2).
3.5
cut grading
grading of the perfection of diamond processing technology by the proportion and finish, made through measurement and observation
3.5.1
round brilliant cut
round cut made up of 57 or 58 facets according to a certain pattern (see Figure 1). Nomenclature of the parts of a round brilliant cut is as shown in Figures 2 and 3. It may be referred to as “round cut”.
Top view of the crown Top view of the pavilion
Figure 1 Schematic top view of the crown and pavilion of round brilliant cut
Figure 2 Schematic side view of round brilliant cut
Figure 3 Schematic facets of round brilliant cut
3.5.2
diameter
diameter of the round horizontal plane of diamond girdle. The maximum value is called the maximum diameter, and the minimum value is called the minimum diameter. Half (maximum diameter + minimum diameter) value is called the average diameter.
3.5.3
total depth
vertical distance from the diamond table to the culet
3.5.4
girdle
the part of the largest circumference in a diamond
3.5.5
crown
the part above the girdle, containing 33 facets
3.5.6
pavilion
the part below the girdle, containing 24 or 25 facets
3.5.7
table facet
the octagonal facet of crown
3.5.8
upper main facet (bezel facet)
quadrilateral facet of crown
3.5.9
star facet
the triangular facet between the bezel facet and the table facet
3.5.10
upper girdle facet
the triangular facet between the girdle and the bezel facet
3.5.11
pavilion main facet
quadrilateral facet of pavilion
3.5.12
lower girdle facet
the triangular facet between the girdle and the pavilion main facet
3.5.13
culet
a small point or octagonal facet, where the pavilion main facets meet
3.5.14
crown angle
α
the angle between the bezel facet and the horizontal plane of the girdle
3.5.15
pavilion angle
β
the angle between the pavilion main facet and the horizontal plane of the girdle
3.5.16
proportion
the percentage of a part to the average diameter, including the following elements (see Figure 4 for details)
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Color grading
5 Clarity grading
6 Cut grading
7 Diamond weight
8 Diamond grading certificate
Annex A (Informative) Common types of internal and external characteristics of diamond
Annex B (Normative) Grading rules for set diamonds
Annex C (Normative) Proportion grading tables
Annex D (Informative) Table for suggested carat weight of diamond
