prEN ISO 24016

SLOVENSKI STANDARD
01-januar-2026
Nakit in plemenite kovine - Ocenjevanje poliranih diamantov - Terminologija,
klasifikacija in preskusne metode (ISO 24016:2020, vključno s popravljeno
različico 2024-03)
Jewellery and precious metals - Grading polished diamonds - Terminology, classification
and test methods (ISO 24016:2020, including corrected version 2024-03)
Schmuck und Edelmetalle - Gradierung geschliffener Diamanten - Begriffe,
Klassifizierung und Prüfverfahren (ISO 24016:2020, einschließlich korrigierte Fassung
2024-03)
Joaillerie et métaux précieux - Classification des diamants taillés - Terminologie,
graduations et méthodes d’essai (ISO 24016:2020, y compris version corrigée 2024-03)
Ta slovenski standard je istoveten z: prEN ISO 24016
ICS:
01.040.39 Finomehanika. Nakit Precision mechanics.
(Slovarji) Jewellery (Vocabularies)
39.060 Nakit Jewellery
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

International
Standard
ISO 24016
First edition
Jewellery and precious metals —
2020-09
Grading polished diamonds —
Terminology, classification and
Corrected version
test methods
2024-03
Joaillerie et métaux précieux — Classification des diamants taillés
— Terminologie, graduations et méthodes d’essai
Reference number
ISO 24016:2020(en) © ISO 2020
ISO 24016:2020(en)
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 24016:2020(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 5
4.1 The use of the word “diamond” .5
4.2 Composite stones/assembled stones .5
5 Mass and measurements . 6
5.1 Mass .6
5.2 Measurements . .6
6 Colour . 6
6.1 General .6
6.1.1 Colourless to yellow, brown and grey (D to L) .6
6.1.2 Colourless to yellow, brown and grey (M to Z) .6
6.1.3 Other hues .7
6.2 Colour grades (colourless to yellow, brown and grey) .7
6.3 Colour grades (other than for yellow, brown and grey) .7
6.4 Fluorescence .9
7 Clarity .10
7.1 General .10
7.2 Clarity grades .10
7.3 Clarity characteristics .10
7.4 Laser drilling .10
8 Cut .12
8.1 Cut characteristics . 12
8.2 Shape . 12
8.3 Proportions. 12
8.3.1 Description . 12
8.3.2 Basis for descriptions of proportions . 12
8.3.3 Table size (percentage) . 13
8.3.4 Crown height (percentage) and/or crown angle (degrees) . 13
8.3.5 Pavilion depth (percentage) and/or pavilion angle (degrees) . 13
8.3.6 Girdle thickness (percentage) and description . 13
8.3.7 Culet size (percentage) and description . 13
8.3.8 Total depth/height .14
8.3.9 Proportions comment .14
8.4 Finish .17
8.4.1 Polish .17
8.4.2 Symmetry .17
9 Identification .18
10 Testing mass and measurements .18
10.1 Testing mass .18
10.2 Testing measurements .18
11 Testing and grading colour and fluorescence.18
11.1 Cleaning of masterstones .18
11.2 Masterstones for colour .18
11.3 Procedure .19
11.3.1 Precautions .19
11.3.2 Cleaning .19

iii
ISO 24016:2020(en)
11.3.3 Comparisons .19
11.3.4 Round stones .19
11.3.5 Fancy shapes .19
11.3.6 Colours . . .19
11.3.7 Lighting .19
11.3.8 Positioning .19
11.3.9 The grade . 20
11.3.10 Master-eye effect .21
11.4 Description of fluorescence. 22
11.4.1 Equipment and References . 22
11.4.2 Masterstones for fluorescence . 22
11.4.3 Working conditions and methodology . 22
11.4.4 Fluorescence, other than blue . . 22
12 Testing and grading clarity .23
12.1 General . 23
12.2 Apparatus . 23
12.3 Procedure . 23
12.3.1 General . 23
12.3.2 Lighting . 23
12.3.3 Distance . 23
12.3.4 Plotting . 23
12.3.5 Plotting symbols . 25
12.3.6 Laser drill holes . 26
12.3.7 Surface grain lines . 26
12.3.8 Internal graining .27
12.3.9 General .27
13 Testing shape .27
14 Testing and grading proportions .27
14.1 Appropriate instruments .27
14.2 Description .27
14.2.1 Table sizes.27
14.2.2 Crown height .27
14.2.3 Pavilion depth . 28
14.2.4 Girdle thickness . 28
14.2.5 Culet size . 28
14.3 Proportions comments . 28
15 Grading of symmetry and polish (Finish) .28
15.1 Symmetry . 28
15.2 Polish . 30
16 Expression of results .31
17 Comments .31
18 Diamond grading report .32
Annex A (normative) Clarity, polish and symmetry characteristics .34
Annex B (informative) Clarity examples .37
Bibliography .53

iv
ISO 24016:2020(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 174, Jewellery and precious metals.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
This corrected version of ISO 24016:2020 incorporates the following corrections:
— In Table 2, lines I and K, the "+" signs have been deleted.

v
ISO 24016:2020(en)
Introduction
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.
vi
International Standard ISO 24016:2020(en)
Jewellery and precious metals — Grading polished diamonds
— Terminology, classification and test methods
1 Scope
This document specifies the terminology, classification and the methods that are used for the grading and
description of single unmounted polished diamonds over 0,25 carat (ct).
This document applies to natural, unmounted, polished diamonds. It is not to be used for fancy coloured
diamonds, synthetic diamonds, treated diamonds (other than is allowed for in 7.4), nor for assembled stones.
2 Normative references
The following document is referred to in the text in such a way that some or all of their content constitutes
requirements 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.
ISO 18323, Jewellery — Consumer confidence in the diamond industry
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18323 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
polished diamond
diamond with a defined cut (3.5)
3.1.1
diamond
mineral consisting essentially of carbon crystallised in the isometric (cubic) crystal system, with a hardness
on the Mohs’ scale of 10, a specific gravity of approximately 3,52 and a refractive index of approximately
2,42, created by nature
Note 1 to entry: The denomination “diamond” without further specification always implies “natural diamond”. These
two terms are equivalent and carry the same meaning.
3.1.2
treated diamond
diamond (3.1.1) having undergone any human intervention other than cutting, polishing, cleaning and
setting, to permanently or non-permanently change its appearance
EXAMPLE Coating, fracture filling, heating, irradiation, laser drilling, HPHT treatment or any other physical or
chemical process.
ISO 24016:2020(en)
3.1.3
synthetic diamond
laboratory-grown diamond
laboratory-created diamond
artificial product that has essentially the same chemical composition, crystal structure and physical
(including optical) properties as a diamond (3.1.1)
Note 1 to entry: The English terms laboratory-created diamond or laboratory-grown diamond may be used
synonymously with synthetic diamond. Where there is no acceptable local direct translation of the English terms
laboratory grown diamond or laboratory created diamond then only the translation of the term synthetic diamond
should be used.
Note 2 to entry: Abbreviations such as "lab grown", "lab created" "lab diamond" or "syn diamond" shall not be used.
Note 3 to entry: The word “laboratory” refers to the facility which produces the synthetic diamonds. This should
not to be confused with a gemmological laboratory that is dedicated to the analysis, authentication, identification,
classification (grading) of diamonds.
3.1.4
composite stone
assembled stone
stone constructed of two or more parts
3.2 Internal characteristics
3.2.1
bearding
tiny feathers (3.2.8) extending in from the girdle
3.2.2
bruise
surface percussion mark, accompanied by tiny, root-like feathers (3.2.8)
3.2.3
cavity
large or deep opening
3.2.4
chip
damage, usually occurring along the girdle or culet, which alters the outline of the stone
Note 1 to entry: Also to be considered as an external characteristic (see 3.3.4) depending upon depth.
3.2.5
cleavage
large feather (3.2.8) occurring in a plane, parallel to a crystal face
3.2.6
cloud
hazy or milky area made up of a number of very small inclusions (3.10)
3.2.7
crystal
mineral crystal included in a diamond (3.1.1)
3.2.8
feather/fracture
separation or break due to either cleavage (3.2.5) or fracture, often white and feathery in appearance
3.2.9
grain centre
small area of concentrated crystal (3.2.7) structure distortion

ISO 24016:2020(en)
3.2.10
internal graining
internal indications of irregular crystal (3.2.7) growth
3.2.10.1
coloured graining
graining which appears as coloured streaks
3.2.10.2
reflective graining
graining which appears as a reflective plane
3.2.10.3
whitish graining
graining which may appear as whitish streaks or may give the stone a hazy (cloudy) appearance which
decreases transparency
3.2.11
indented natural
natural (3.3.6) that penetrates the stone
Note 1 to entry: Also to be considered as an external characteristic (see 3.3.15) depending upon depth.
3.2.12
knot
included diamond (3.1.1) crystal which reaches the surface
3.2.13
laser drilling
burning a channel with a laser between the surface of a diamond (3.1.1) and an inclusion (3.10) (generally
black), the channel being used as a conduit to allow a chemical treatment of the inclusion (3.10) with the
purpose of making the inclusion (3.10) less visible
3.2.14
needle
long, thin included crystal (3.2.7) which looks like a tiny rod
3.2.15
nick
minor damage, occurring along the girdle, the culet or facet edge, which does not significantly affect the
outline of the stone
Note 1 to entry: Also to be considered as an external characteristic (see 3.3.7) depending upon depth.
3.2.16
pinpoint
very small inclusion (3.10); under 10x normally seen as a tiny dot, either singly or in groups or strings
3.2.17
reduced transparency
cloudy, milky, or hazy appearance of the whole or part of a diamond (3.1.1) due to internal features that may
or may not be visible at 10x magnification
3.2.18
twinning wisp
inclusions (3.10) usually located in a plane, which occur as a result of the change in orientation of the diamond
crystal structure
3.2.19
etch channel
high-temperature magma erodes the weak area of the diamond (3.1.1), leaving behind tubular traces
extending from the surface to the inside, with a quadrangle opening

ISO 24016:2020(en)
3.3 External characteristics
3.3.1
abrasion
tiny nicks (3.3.7) along facet junction’s or culet, producing white fuzzy lines instead of sharp facet edges
3.3.2
bruting lines
tiny lines on a girdle not displaying a feather-like appearance
3.3.3
burn mark
surface clouding caused by excessive heat, or uneven polished surface
3.3.4
chip
damage, usually occurring along the girdle or culet, which alters the outline of the stone
Note 1 to entry: Also to be considered as an internal characteristic (see 3.2.4) depending upon depth.
3.3.5
extra facet
facet located without regard for symmetry and not required by the cutting style
3.3.6
natural
part of the original crystal (3.2.7) surface remaining on the polished stone
3.3.7
nick
minor damage, occurring along the girdle, the culet or facet edge, which does not significantly affect the
outline of the stone
Note 1 to entry: Also to be considered as an internal characteristic (see 3.2.15) depending upon depth.
3.3.8
pit
tiny opening, often looking like a white dot
3.3.9
polish line
tiny parallel lines left by polishing; fine parallel ridges confined to single facet, caused by crystal (3.2.7)
structure irregularities; or tiny, parallel, polished grooves produced by irregularities in the scarify surface
3.3.10
pitted girdle
very rough bruted girdle surface
3.3.11
scratch
linear indentation normally seen as a fine white line across a facet
3.3.12
surface grain line
surface indication of structural irregularity which is not seen internally; may resemble faint facet-junction
lines, or cause a grooved or wavy surface; often the lines cross facet junctions
3.3.13
lizard skin
transparent concave wave texture on the surface of a polished diamond (3.1.1), usually parallel to the
direction of the cleavage (3.2.5) surface

ISO 24016:2020(en)
3.3.14
inscription
mark on the surface of or in a diamond (3.1.1)
3.3.15
indented natural
natural that penetrates the stone
Note 1 to entry: Also to be considered as an internal characteristic (see 3.2.11) depending upon depth.
3.4
naked eye
naked (unaided) eye, or visible to the eye through glasses adjusting an anomalous eyesight to normal
3.5
cut
shape (3.6), proportions, polish and symmetry of a diamond (3.1.1)
Note 1 to entry: The term finish encompasses polish and symmetry.
3.6
shape/form
outline of a diamond (3.1.1)when viewed perpendicular to the table facet
3.7
diamond loupe
achromatic and aplanatic, triplet type, 10x magnifying lens
Note 1 to entry: The frame of the loupe shall be of a neutral ‘colour’.
3.8
first generation masterstone
diamond (3.1.1) that has been selected by direct comparison with the relevant masterstone in the set of
masterstones originally used to establish the D to Z grades, as specified in 6.1 and equal in hue, tone and
saturation to the relevant original masterstone
3.9
second generation masterstone
diamond (3.1.1) that has been selected by direct comparison with the relevant first generation masterstone
(3.8) and equal in hue, tone and saturation to the relevant first generation masterstone (3.8)
3.10
inclusion
physical alteration to the interior of a diamond (3.1.1)
4 General
4.1 The use of the word “diamond”
It is unnecessary to note the genesis of a diamond, as the use of the word “diamond” alone and without
qualification states that it is natural.
The word “diamond” alone shall not be used to describe synthetic diamonds no matter which basic material
or methods are used. Products made in this way shall be clearly referred to as “synthetic diamond” and shall
not be graded according to this document.
4.2 Composite stones/assembled stones
Composite stones/assembled stones shall be clearly identified and shall not be graded.

ISO 24016:2020(en)
5 Mass and measurements
5.1 Mass
The mass of a diamond shall be expressed in metric carats (ct), one carat is equivalent to 200 mg (1/5 g). The
mass of a diamond shall be stated in carats to two decimal places.
NOTE It is acceptable verbally to express one-hundredth of a carat as a “point”.
Mass shall be rounded upwards if the third decimal is a 9.
EXAMPLES
— 0,996 → 0,99 ct
— 0,998 → 0,99 ct
— 0,999 → 1,00 ct
Mass may be stated to three decimal places if the accuracy of the weighing equipment is accurate to this degree.
5.2 Measurements
The measurements of a diamond shall be expressed in millimetres to two decimal places.
The following measurements shall be contained in the diamond grading report (Clause 18):
— round shape: minimum diameter, maximum diameter and depth (total height);
— fancy shape: length, width and depth (total height). Length shall be the maximum measurement in the
vertical line of the plotted diagram and width shall be the maximum measurement in the horizontal line
of the plotted diagram.
6 Colour
6.1 General
Diamond colours shall be divided into the following three main categories (see 6.1.1, 6.1.2 and 6.1.3).
NOTE For all main categories (see 6.1.1, 6.1.2 and 6.1.3), photometric measurements intended for colour grade
determination have no conclusive value at present.
6.1.1 Colourless to yellow, brown and grey (D to L)
The colour of diamond within the D to L grade range shall be determined by visual comparison with
masterstones of first or second generation which is equal in hue, tone and saturation to the official CIBJO
set of masterstones for determining the colour grades. The determination shall be carried out by a trained
observer with normal eyesight (see 3.4) and colour discrimination, under an artificial light source, the
specification for which ranges from D to D [International Commission on Illumination (CIE) standard
55 65
illuminant].
The colour grade shall be described by the letter or letter range between D and L, (in capital letters) with or
without the colour corresponding terms in Tables 1 and 2.
Colour comparison shall refer to masterstones of first or second generation.
NOTE Optionally the hue of a diamond when different than yellow can be mentioned in addition to the colour grade.
6.1.2 Colourless to yellow, brown and grey (M to Z)
Those colour grades are not currently covered by the present document.

ISO 24016:2020(en)
6.1.3 Other hues
Apart from those diamonds referred to in 6.1.1 and 6.1.2 there are those diamonds that are darker in tone
and/or higher in saturation than the Z colour grade and diamonds with other noticeable hues or tones and
these are coloured diamonds. In this category, the specific term “fancy” shall precede the colour description
of a coloured diamond.
6.2 Colour grades (colourless to yellow, brown and grey)
The colour grades that shall be used are given in Table 1. The German, French, Italian, Chinese and
Scandinavian equivalent terms shall be as given in Table 2.
6.3 Colour grades (other than for yellow, brown and grey)
Diamonds with colours other than yellow, brown or grey, in which the colour is not visible in the face-
up position, shall be graded in accordance with the colour grading scale (see Table 1). The grade shall be
described either with the letter grade or by stating the term “faint” followed by the hue, or by both.

ISO 24016:2020(en)
Table 1 — Colour grading scale
GIA
CIBJO
Gemological
The World Jewellery NOTES
Institute
Confederation
of America
NOTE 1  For diamonds weighing under 0,47 ct, the grades D EW+ and E
Exceptional white + D
EW can be combined into one grade as Exceptional White or D-E.
Exceptional white E
NOTE 2  For diamonds weighing under 0,47 ct, the grades F RW+ and G
Rare white + F
RW can be combined into one grade as Rare White or F-G.
Rare white G
White H
Slightly tinted white I NOTE 3  Combined letter grades including and below I can be used.
NOTE 4  For grades I to J the term "equivalent colour grade" can be used
Slightly tinted white J
in conjunction with the letter grade for those diamonds that have brown
or grey present.
Tinted white K NOTE 5  Combined letter grades including and below K can be used.
NOTE 6  For grades K to L the term "equivalent colour grade" can be used
Tinted white L in conjunction with the letter grade for those diamonds that have brown
or grey present.
M NOTE 7  Combined letter grades including and below M can be used.
NOTE 8  Descriptions indicating the presence of brown or grey can be
N
given for Grades M and below with or without using the letter grades if
O
the hue / tone description is prefixed with "light".
P
Q
R
S
Tinted T
U
V
W
X
Y
Z
ISO 24016:2020(en)
Table 2 — Corresponding terms for colour grades
a
GIA CIBJO (The World Jewellery Confederation) Chinese
national Scan.D.N
English German French Italian
standard
Exceptional Blanc Bianco extra
D D Hochfeines Weiss + D D D D 100 River D
white + exceptionnel + eccezionale +
Exceptional Blanc Bianco extra
E E Hochfeines Weiss E E E E 99 River E
white exceptionnel eccezionale
Top
F Rare white + F Feines Weiss + F Blanc extra + F Bianco extra + F F 98 F
Wesselton
Top
G Rare white G Feines Weiss G Blanc extra G Bianco extra G G 97 G
Wesselton
H White H Weiss H Blanc H Bianco H H 96 Wesselton H
Slightly tinted Leicht getöntes
I I I Blanc nuancé I Bianco sfumato I I 95 Top crystal I
white Weiss
Slightly tinted Leicht getöntes
J J J Blanc nuancé J Bianco sfumato J J 94 Crystal J
white Weiss
Légèrement Bianco leggermente
K Tinted white K Getöntes Weiss K K K K 93 Top cape K
teinté colorito
Légèrement Bianco leggermente
L Tinted white L Getöntes Weiss L L L L 92 Cape L
teinté colorito
M M M M M M 91 Cape M
N N N N N N 90 Cape N
O O O O O P P P P P Cape P
Q Q Q Q Q Cape Q
R R R R R Cape R
S S S S S Cape S
T Tinted T Getönt T Teinté T Colorito T Cape T
U U U U U Cape U
V V V V V Cape V
W W W W W Cape W
X X X X X Cape X
Y Y Y Y Y Cape Y
Z Z Z Z Z Cape Z
a
Gemological Institute of America.
6.4 Fluorescence
The fluorescence of diamond shall be determined by visual comparison with masterstones of first or second
generation which is equal in hue and degree to the official CIBJO set of masterstones for determining the
fluorescence. The determination shall be carried out by a trained observer with normal eyesight (see 3.4)
and colour discrimination.
The degree of fluorescence shall be characterized in accordance with Table 3.
Table 3 — Description of degree of fluorescence
Degree of fluorescence Colour of fluorescence
none or nil optional
faint or slight optional
medium optional
strong optional
The colour of fluorescence may be mentioned together with the degree of fluorescence.

ISO 24016:2020(en)
7 Clarity
7.1 General
Clarity shall be determined by a trained observer with normal eyesight (see 3.4) using a diamond loupe,
under an artificial source of light, the specification of which is D55 to D65 (CIE standard illuminant).
The following aspects of the internal characteristics/inclusions and external characteristics/blemishes
shall be considered when determining the clarity grade:
— size;
— nature;
— number;
— position;
— brightness/colour;
— mirrored images.
NOTE Diamonds that are beyond the P3/I3 grade are known as rejection grade and are considered as being
outside the clarity grading scale.
7.2 Clarity grades
The clarity grades shall be distinguished and defined in accordance with Tables 4 and 5.
7.3 Clarity characteristics
Clarity shall be considered in accordance with Tables 4 and 5 and A.1 and A.2.
See also definitions 3.2 and 3.3.
7.4 Laser drilling
All diamonds that have been drilled with a laser shall be referred to as “Laser Drilled” in the Comment
section, and can be graded. No other treated diamonds shall be graded according to this document.

ISO 24016:2020(en)
Table 4 — Clarity characteristics
Flawless (FL) Loupe Clean (LC)
FL diamonds shall be free from internal characteristics/inclusions and external char- LC diamonds shall be free
acteris
...