ISO/FDIS 787-24

• Abstract:

  The method specified provide an instrumental alternative to those described in ISO 787/16 and ISO 787/17. Equal masses of a coloured material are separately dispersed in the same mass of the same white pigment paste. The reflectivity of each dispersion is measured photometrically. From the corresponding values of K/S the relative tinting strength is given. For measurement of the relative scattering power equal masses of a white test material and an agreed reference pigment are separately dispersed in the same mass of the same black pigment paste. The reflectivity of each dispersion is measured photometrically at 550 nm. From the corresponding values of K/S the relative scattering power is given.

• Status: Not Published
• ICS: 87.060.10 - Pigments and extenders
• Technical Committee: ISO/TC 256 - Pigments, dyestuffs and extenders
• Drafting Committee: ISO/TC 256/WG 3 - General test methods for colorants and extenders
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 25-Jun-2026
• Completion Date: 25-Jun-2026

• Consolidates: FprEN ISO 787-24 - General methods of test for pigments and extenders - Part 24: Photometric methods for determining the relative tinting strength of coloured pigments and the relative scattering power of white pigments (ISO/FDIS 787-24:2026)
• Effective Date: 12-Feb-2026
• Consolidates: ISO/IEC 19075-7:2021 - Information technology — Guidance for the use of database language SQL — Part 7: Polymorphic table functions
• Effective Date: 11-Nov-2023
• Revises: ISO 787-24:1985 - General methods of test for pigments and extenders — Part 24: Determination of relative tinting strength of coloured pigments and relative scattering power of white pigments — Photometric methods
• Effective Date: 28-Oct-2023

Overview

ISO/FDIS 787-24 specifies standardized photometric methods for determining the relative tinting strength of coloured pigments and the relative scattering power of white pigments. Developed by the International Organization for Standardization (ISO), this document provides clear, instrumental alternatives to the visual methods described in ISO 787-16 and ISO 787-17. By utilizing photometric analysis, the standard delivers greater accuracy and repeatability in measuring pigment performance, supporting quality control and product consistency in industries that utilize pigments and extenders.

The standard covers procedures for dispersing pigments in defined resin pastes, measuring reflectivity using photometric equipment, and calculating relative tinting strength or scattering power based on the Kubelka-Munk theory.

Key Topics

• Photometric Testing Methods

  • Instrumental techniques replace subjective visual assessment
  • Use of spectrophotometers and colorimeters for accurate reflectivity measurements

• Determining Relative Tinting Strength

  • Coloured pigments are compared by dispersing equal masses in a white pigment paste
  • The reflectivity of each dispersion is measured and the relative tinting strength is calculated

• Determining Relative Scattering Power

  • White pigments are compared by dispersing equal masses in a black pigment paste
  • Photometric measurement at 550 nm or using a Y-filter determines the relative scattering power

• Standardized Sample Preparation

  • Detailed requirements for materials, including alkyd resin composition and properties for titanium dioxide and carbon black pastes
  • Use of calibrated equipment such as triple-roll mills and automatic mullers

• Calculation Methods

  • Application of the Kubelka-Munk equation (K/S values) for result expression
  • Inclusion of up-to-date terminology and reference criteria according to the latest ISO standards

Applications

ISO/FDIS 787-24 is extensively used in sectors where pigment quality and performance are critical, such as:

• Paints and Coatings: Ensures color consistency and opacity in decorative, automotive, and industrial finishes
• Plastics Manufacturing: Provides objective data to adjust formulations for colored and white polymers
• Printing Inks: Supports reproducibility in print media through standardized pigment strength comparisons
• Quality Control Laboratories: Offers reliable procedures for ongoing pigment and extender verification
• Pigment and Extender Production: Assists manufacturers in benchmarking new products against reference materials

By standardizing photometric methods, the document helps organizations minimize variability, meet regulatory requirements, and ensure customer satisfaction by delivering products with predictable and stable color properties.

Related Standards

ISO/FDIS 787-24 is part of the broader ISO 787 series, which addresses general methods of test for pigments and extenders. Other relevant standards include:

• ISO 787-16: Visual comparison of tinting strength of colored pigments
• ISO 787-17: Comparison of relative scattering power of white pigments by visual means
• ISO 591-1: Titanium dioxide pigments for paints - Specifications and test methods
• ISO 15528: Sampling of paints, varnishes, and raw materials
• ISO 18314-2 and ISO 18314-3: Analytical colorimetry-Kubelka-Munk equation applications and special indices

Through alignment with these documents, ISO/FDIS 787-24 ensures a comprehensive approach to pigment evaluation, supporting international trade, regulatory compliance, and technical interoperability.

Keywords: ISO 787-24, photometric methods, relative tinting strength, scattering power, pigments, extenders, Kubelka-Munk, reflectivity, color measurement, pigment testing, standardization, quality control.

FINAL DRAFT
International
Standard
ISO/TC 256
General methods of test for
Secretariat: DIN
pigments and extenders —
Voting begins on:
2026-06-25
Part 24:
Photometric methods for
Voting terminates on:
2026-08-20
determining the relative tinting
strength of coloured pigments and
the relative scattering power of
white pigments
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 256
General methods of test for
Secretariat: DIN
pigments and extenders —
Voting begins on:
Part 24:
Photometric methods for
Voting terminates on:
determining the relative tinting
strength of coloured pigments and
the relative scattering power of
white pigments
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Terms related to coloured and black pigments .2
3.2 Terms related to white pigments .2
3.3 Terms related to reflectivity .3
3.4 Terms related to reflectance factor .3
4 Principle . 3
4.1 General .3
4.2 Coloured and black pigments .3
4.3 White pigments . .4
5 Materials and equipment . 4
6 Apparatus . 5
7 Sampling . 6
8 Procedure . 6
8.1 Determination of relative tinting strength .6
8.1.1 Test pigment dispersion . .6
8.1.2 Reference pigment dispersion .7
8.1.3 Preparation of test films .7
8.1.4 Measurement of ϱ or R .7
∞ ∞
8.2 Determination of relative scattering power .7
8.2.1 General .7
8.2.2 Test pigment dispersion . .7
8.2.3 Reference pigment dispersion .8
8.2.4 Preparation of test films .8
8.2.5 Measurement of ϱ or R .8
∞ ∞
9 Expression of results . 8
10 Test report . 8
Annex A (informative) Reflectivity and Kubelka-Munk analysis .10
Bibliography .11

iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 256, Pigments, dyestuffs and extenders, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 298,
Pigments and extenders, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 787-24:1985), which has been technically
revised.
The main changes are as follows:
— the introduction has been deleted;
— the normative references have been updated;
— in Clause 3, the definitions have been updated and, where necessary, aligned with ISO 18451-1;
— 3.1.3 “absorbance index” has been changed to “absorption index”;
— 4.1 has been added;
— in 4.2, “K ” has been replaced by “C “ as symbol for relative tinting strength;
r rel
— in 4.2 and 8.1.4, the method has been opened to other tinting strength criterion, including a reference to
ISO 18314-2;
— the characteristic “nigrometer index value” and its requirement have been changed to “blackness value
M ” for the characteristic and to “203 to 215” for the requirement, and ISO 18314-3 has been added as a
Y
test method (Clause 5, Table 2);
2 2
— the requirement for “specific surface area (BET)” has been changed to “25 m /g to 33 m /g” for carbon
black pigment (Clause 5, Table 2);
— the requirement for the pH value has been changed to “6 to 9” for carbon black pigment (Clause 5, Table 2);

iv
— ISO 9277 has been added as the test method for the specific surface area (BET) for fumed silica (Clause 5,
Table 3);
— in 6.3, a reference was included which described the possibility of measuring paste films on a moving
carrier without any contact;
— in 6.4, additional light sources for the tristimulus colorimeter were included;
— Annex A has been modified and subdivided into A.1 and A.2;
— Annex B has been deleted;
— a bibliography has been added.
A list of all parts in the ISO 787 series can be found on the ISO website.
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.

v
FINAL DRAFT International Standard ISO/FDIS 787-24:2026(en)
General methods of test for pigments and extenders —
Part 24:
Photometric methods for determining the relative tinting
strength of coloured pigments and the relative scattering
power of white pigments
1 Scope
This document specifies photometric methods of test for comparing in the visible spectrum:
a) the tinting strength of two similar coloured pigments dispersed in an alkyd resin without a drier;
b) the scattering power of two white pigments of the same type dispersed in an alkyd resin without a
drier.
This document does not apply to the comparison of coloured pigments that on reduction differ greatly in
colour.
2 Normative references
The following documents are 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 591-1, Titanium dioxide pigments for paints — Part 1: Specifications and methods of test
ISO 787-2, General methods of test for pigments and extenders — Part 2: Determination of matter volatile at
105 °C
ISO 787-9, General methods of test for pigments and extenders — Part 9: Determination of pH value of an
aqueous suspension
ISO 787-10, General methods of test for pigments and extenders — Part 10: Determination of density —
Pyknometer method
ISO 3219 (all parts), Rheology
ISO 2114, Plastics (polyester resins) and paints and varnishes (binders) — Determination of partial acid value
and total acid value
ISO 4629 (all parts), Binders for paints and varnishes — Determination of hydroxyl value
ISO 4652, Rubber compounding ingredients — Carbon black — Determination of specific surface area by
nitrogen adsorption methods — Single-point procedures
ISO 6209, Rubber compounding ingredients — Carbon black — Determination of solvent-extractable material
ISO 9277, Determination of the specific surface area of solids by gas adsorption — BET method
ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling

ISO 18314-2, Analytical colorimetry — Part 2: Saunderson correction, solutions of the Kubelka-Munk equation,
tinting strength, depth of shade and hiding power
ISO 18314-3, Analytical colorimetry — Part 3: Special indices
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms related to coloured and black pigments
3.1.1
tinting strength
colour strength
measure of the ability of a colourant to colour other materials because of its absorptive power
[SOURCE: ISO 18451-1:2019, 3.122]
3.1.2
spectral absorption coefficient
K(λ)
fraction of the diffusely incident spectral radiant flux of wavelength λ that is absorbed in an elementary
layer within a material, divided by the thickness of the layer (Kubelka-Munk analysis)
Note 1 to entry: K(λ) is a measure of the tinting strength (3.1.1) of coloured pigments in a material.
3.1.3
absorption index
K (λ)
p
spectral absorption coefficient (3.1.2) of the pigmented binder divided by the pigment concentration C :
m
K 

K  

p
C
m
where C is the pigment concentration, for example, expressed as the ratio by mass of pigment to binder
m
3.1.4
relative tinting strength
relative colour strength
C
rel
percentage ratio of the tinting strength (3.1.1) of the colourant under test related to the tinting strength
(3.1.1) of a reference colourant
[SOURCE: ISO 18451-1:2019, 3.105, modified — the symbol C has been added.]
rel
3.2 Terms related to white pigments
3.2.1
scattering power
ability of a pigmented medium to partly diffuse the incident light

3.2.2
spectral scattering coefficient
S(λ)
net transfer of spectral radiant flux of wavelength λ in the outward direction from an elementary layer
within a body of material illuminated from outside, divided by the product of the thickness of the layer and
the difference between the magnitude of the flux in the two directions through the layer (Kubelka-Munk
analysis)
Note 1 to entry: S(λ) is a measure of the scattering power (3.2.1) of white pigments in a material and is expressed in
units of reciprocal film thickness.
3.2.3
scattering index
S (λ)
p
spectral scattering coefficient (3.2.2) of the pigmented binder divided by the pigment concentration C :
m
S 

S  

p
C
m
3.2.4
relative scattering power
percentage ratio of the scattering power of the white pigment under test to the scattering power of a
reference white pigment
[SOURCE: ISO 18451-1:2019, 3.104, modified — in the definition “scattering index” has been replaced twice
by “scattering power”.]
3.3 Terms related to reflectivity
3.3.1
reflectivity
ϱ
∞
reflectance of a paste or a paint film whose thickness is such that any further increase in thickness gives no
further change in reflectance
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ISO /TC 256/WG 3
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Date: 2026-05-11
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Secretariat: DIN
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General methods of test for pigments and extenders —
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Part 24:
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Photometric methods for determining the relative tinting strength
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pigments
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FDIS stage
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© ISO 2026
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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
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ISO copyright office
from edge: 0.5 cm
CP 401 • Ch. de Blandonnet 8
CH--1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.orgwww.iso.org
Published in Switzerland
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Formatted: FooterPageRomanNumber, Space After: 0
pt, Line spacing: single
ii © ISO 2025 2026 – All rights reserved
ii
Formatted: Font: Bold
Formatted: HeaderCentered, Left
Contents Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
Foreword . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Terms related to coloured and black pigments . 2
3.2 Terms related to white pigments . 3
3.3 Terms related to reflectivity . 3
3.4 Terms related to reflectance factor . 4
4 Principle . 4
4.1 General. 4
4.2 Coloured and black pigments . 4
4.3 White pigments . 4
5 Materials and equipment . 5
6 Apparatus . 6
7 Sampling . 7
8 Procedure . 7
8.1 Determination of relative tinting strength . 7
8.2 Determination of relative scattering power . 8
9 Expression of results . 9
10 Test report . 9
Annex A (informative) Reflectivity and Kubelka-Munk analysis . 11
Bibliography . 12

Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 For coloured and black pigments. 2
3.2 For white pigments . 2
4 Principle . 3
4.1 General. 3
4.2 Coloured and black pigments . 3
4.3 White pigments . 4
5 Materials and equipment . 4
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6 Apparatus . 5
Formatted: Font: 10 pt
7 Sampling . 6
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8 Procedure . 6
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8.1 Determination of relative tinting strength . 6
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8.1.1 Test pigment dispersion . 6
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8.1.2 Reference pigment dispersion . 6
8.1.3 Preparation of test films . 7
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© ISO 2026 – All rights reserved
iii
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Formatted: HeaderCentered
8.1.4 Measurement of ϱ or R . 7
∞ ∞
8.2 Determination of relative scattering power . 7
8.2.1 General. 7
8.2.2 Test pigment dispersion . 7
8.2.3 Reference pigment dispersion . 8
8.2.4 Preparation of test films . 8
8.2.5 Measurement of ϱ or R . 8
∞ ∞
9 Expression of results . 8
10 Test report . 8
Annex A (informative) Reflectivity and absorption and scattering coefficients . 9
Annex B (informative) K/S values as a function of measured ϱ or R . 10
∞ ∞
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iv © ISO 2025 2026 – All rights reserved
iv
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Formatted: HeaderCentered, Left
Foreword Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
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 document 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).
Formatted: English (United Kingdom)
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
patent rights.
Any trade name used in this document is information given for the convenience of users and does not
Formatted: English (United Kingdom)
constitute an endorsement.
Formatted: Adjust space between Latin and Asian text,
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
Adjust space between Asian text and numbers
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Formatted: Default Paragraph Font
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
Formatted: Default Paragraph Font
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
Formatted: Default Paragraph Font
This document was prepared by Technical Committee ISO/TC 256, Pigments, dyestuffs and extenders, in
Formatted: Default Paragraph Font
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 298,
Formatted: Adjust space between Latin and Asian text,
Pigments and extenders, in accordance with the Agreement on technical cooperation between ISO and CEN
Adjust space between Asian text and numbers, Tab
(Vienna Agreement).
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
This third edition cancels and replaces the second edition (ISO 787--24:1985), which has been technically
revised.
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Formatted: Default Paragraph Font
The main changes are as follows:
Formatted: Default Paragraph Font
— — the introduction has been deleted;
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
— — the normative references have been updated;
Formatted: Default Paragraph Font
— — in Clause 3,Clause 3, the definitions have been updated and, where necessary, aligned with
Formatted: Default Paragraph Font
ISO 18451--1;
Formatted: Font: 10 pt
— 3.1.33.1.3 “absorbance index” has been changed to “absorption index”;
Formatted: Font: 10 pt
Formatted: Font: 10 pt
— subclause 4.14.1 has been added;
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— in 4.24.2, “K ” has been replaced by “C “ as symbol for relative tinting strength; Tab stops: Not at 17.2 cm
r rel
Formatted: Font: 11 pt
— — in 4.24.2 and 8.1.4,8.1.4, the method has been opened to other tinting strength criterion, including a
Formatted: FooterPageRomanNumber, Left, Space
reference to ISO 18314--2;
After: 0 pt, Tab stops: Not at 17.2 cm
© ISO 2026 – All rights reserved
v
Formatted: Font: Bold
Formatted: HeaderCentered
— — the characteristic “nigrometer index value” and its requirement have been changed to “blackness value
M ” for the characteristic and to “203 to 215” for the requirement, and ISO 18314--3 has been added as a
Y Formatted: Default Paragraph Font
test method (Clause 5, Table 2);(Clause 5, Table 2);
Formatted: Default Paragraph Font
2 2
Formatted: Default Paragraph Font
— — the requirement for “specific surface area (BET)” has been changed to “25 m /g to 33 m /g” for carbon
black pigment (Clause 5, Table 2);(Clause 5, Table 2);
— — the requirement for the pH value has been changed to “6 to 9” for carbon black pigment (Clause 5,
Table 2);(Clause 5, Table 2);
— — ISO 9277 has been added as the test method for the specific surface area (BET) for fumed silica
Formatted: Default Paragraph Font
(Clause 5, Table 3);(Clause 5, Table 3);
Formatted: Default Paragraph Font
— — in 6.3,in 6.3, a reference was included which described the possibility of measuring paste films on a
moving carrier without any contact;
— — in 6.4,6.4, additional light sources for the tristimulus colorimeter were included;
— — Annex AAnnex A has been modified and subdivided into by A.1A.1 and A.2;A.2;
— — Annex B has been deleted;
— — a bibliography has been added.
A list of all parts in the ISO 787 series can be found on the ISO website.
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Any feedback or questions on this document should be directed to the user’s national standards body. A
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complete listing of these bodies can be found at www.iso.org/members.htmlwww.iso.org/members.html.
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pt, Line spacing: single
vi © ISO 2025 2026 – All rights reserved
vi
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DRAFT International Standard ISO/DIS 787-24:2025(en)
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General methods of test for pigments and extenders —
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Part 24:
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Photometric methods for determining the relative tinting strength of
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coloured pigments and the relative scattering power of white
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pigments
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...
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1 Scope
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This document specifies photometric methods of test for comparing in the visible spectrum:
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a) a) the tinting strength of two similar coloured pigments dispersed in an alkyd resin without a
drier;
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...
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...
b) b) the scattering power of two white pigments of the same type dispersed in an alkyd resin
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without a drier.
...
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This document does not apply to the comparison of coloured pigments that on reduction differ greatly in
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colour.
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2 Normative references
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...
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The following documents are 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, Formatted
...
the latest edition of the referenced document (including any amendments) applies.
Formatted
...
Formatted
ISO 591--1, Titanium dioxide pigments for paints — Part 1: Specifications and methods of test .
Formatted
...
ISO 787--2, General methods of test for pigments and extenders — Part 2: Determination of matter volatile at
Formatted
...
105 °C
Formatted
...
ISO 787--9, General methods of test for pigments and extenders — Part 9: Determination of pH value of an
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...
aqueous suspension
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...
ISO 787--10, General methods of test for pigments and extenders — Part 10: Determination of density —
Formatted
...
Pyknometer method
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...
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ISO 3219 (all parts), Rheology .
Formatted
...
ISO 2114, Plastics (polyester resins) and paints and varnishes (binders) — Determination of partial acid value
Formatted
...
and total acid value
Formatted
...
ISO 4629 (all parts), Binders for paints and varnishes — Determination of hydroxyl value
Formatted
...
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...
ISO 4652, Rubber compounding ingredients — Carbon black — Determination of specific surface area by
nitrogen adsorption methods — Single-point procedures
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...
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ISO 6209, Rubber compounding ingredients — Carbon black — Determination of solvent-extractable material
Formatted
...
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...
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...
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...
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ISO 9277, Determination of the specific surface area of solids by gas adsorption — BET method
...
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ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
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ISO 18314-2, Analytical colorimetry — Part 2: Saunderson correction, solutions of the Kubelka-Munk Formatted
...
equation, tinting strength, depth of shade and hiding power
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...
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ISO 18314--3, Analytical colorimetry — Part 3: Special indices .
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3 Terms and definitions
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For the purposes of this document, the following terms and definitions apply. .
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ISO and IEC maintain terminology databases for use in standardization at the following addresses:
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— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp Formatted
...
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— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
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3.1 Terms related to coloured and black pigments
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...
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...
3.1.1 3.1.1
tinting strength
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...
colour strength
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...
measure of the ability of a colourant to colour other materials because of its absorptive power
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...
[SOURCE: ISO 18451-1:2019, 3.122]
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...
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...
3.1.2 3.1.2
spectral absorption coefficient
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...
K(λ)
Formatted
...
fraction of the diffusely incident spectral radiant flux of wavelength λ that is absorbed in an elementary layer
Formatted
...
within a material, divided by the thickness of the layer (Kubelka-Munk analysis)
Formatted
...
Note 1 to entry: K(λ) is a measure of the tinting strength (3.1.1)(3.1.1) of coloured pigments in a
Formatted
...
material.
Formatted
...
3.1.3 3.1.3
Formatted
...
absorption index
K (λ) Formatted
p
...
spectral absorption coefficient (3.1.2)(3.1.2) of the pigmented binder divided by the pigment concentration Cm:
Formatted
...
Formatted
𝐾𝐾(𝜆𝜆)
...
𝐾𝐾 𝜆𝜆 =
( )
p
𝐶𝐶
m
Formatted
...
𝐾𝐾(𝜆𝜆) Formatted
...
𝐾𝐾 (𝜆𝜆) =
p
𝐶𝐶
m Formatted
...
Formatted
...
where C is the pigment concentration, for example, expressed as the ratio by mass of pigment to binder
m
Formatted
...
3.1.4 3.1.4
Formatted
...
relative tinting strength
Formatted
relative colour strength .
C
rel
Formatted
...
percentage ratio of the tinting strength (3.1.1)(3.1.1) of the colourant under test related to the tinting strength
Formatted
...
(3.1.1)(3.1.1) of a reference colourant
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2 © ISO 2025 2026 – All rights reserved
ISO/DISFDIS 787-24:2026(en)
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[SOURCE: ISO 18451-1:2019, 3.105, modified - The— the symbol C has been added.]
rel
3.2 Terms related to white pigments
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3.2.1 3.2.1
stops: Not at 0.71 cm
scattering power
Formatted: TermNum3, Adjust space between Latin
ability of a pigmented medium to partly diffuse the incident light
and Asian text, Adjust space between Asian text and
numbers
3.2.2 3.2.2
spectral scattering coefficient
S(λ)
Formatted: Regular Italic, Font: Bold, Not Italic
net transfer of spectral radiant flux of wavelength λ in the outward direction from an elementary layer within
Formatted: Regular, Font: Bold
a body of material illuminated from outside, divided by the product of the thickness of the layer and the
Formatted: Regular Italic, Font: Bold, Not Italic
difference between the magnitude of the flux in the two directions through the layer (Kubelka-Munk analysis)
Formatted: Regular, Font: Bold
Note 1 to entry: S(λ) is a measure of the scattering power (3.2.1)(3.2.1) of white pigments in a material
Formatted: Adjust space between Latin and Asian text,
and is expressed in units of reciprocal film thickness.
Adjust space between Asian text and numbers, Tab
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.2.3 3.2.3
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
scattering index
Sp(λ) Formatted: TermNum3, Adjust space between Latin
spectral scattering coefficient (3.2.2)(3.2.2) of the pigmented binder divided by the pigment concentration C : and Asian text, Adjust space between Asian text and
m
numbers
𝑆𝑆(𝜆𝜆)
𝑆𝑆 (𝜆𝜆) =     Formatted: Regular Italic, Font: Bold, Not Italic
p
𝐶𝐶
m
Formatted: Regular Sub, Font: Bold, Not Raised by /
𝑆𝑆(𝜆𝜆)
Lowered by
3.2.4𝑆𝑆 (𝜆𝜆) =
p
𝐶𝐶
m
Formatted: Regular, Font: Bold
3.2.4
Formatted: Regular Italic, Font: Bold, Not Italic
relative scattering power
Formatted: Regular, Font: Bold
percentage ratio of the scattering power of the white pigment under test to the scattering power of a reference
white pigment
Formatted: TermNum3, Adjust space between Latin
and Asian text, Adjust space between Asian text and
[SOURCE: ISO 18451-1:2019, 3.104, modified – In— in the definition “scattering index” has been replaced
numbers
twice by “scattering power”.]
3.3 3.3 Terms related to reflectivity
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Formatted: Heading 2
3.3.1 3.3.1
reflectivity Formatted: TermNum3, Adjust space between Latin
ϱ and Asian text, Adjust space between Asian text and
∞
reflectance of a paste or a paint film of suchwhose thickness is such that any further increase in thickness gives numbers
no further change in reflectance
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Note 1 to entry: For Kubelka-Munk analysis, see ISO 18314-2 and Annex A can be referred
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to.Annex A.
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© ISO 2026 – All rights reserved
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3.4 3.4 Terms related to reflectance factor
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3.4.1 3.4.1
reflectance factor Formatted: TermNum3, Adjust space between Latin
R∞ and Asian text, Adjust space between Asian text and
ratio of the radiant flux reflected in the directions within a given cone by a paste or a paint film to that reflected numbers
in the same directions by a perfect reflecting diffuser identically irradiated, when the thickness of the paste or
Formatted: Regular Italic, Font: Bold, Not Italic
the paint film is such that any further increase in thickness gives no further change in the ratio
4 Principle
4.1 General
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The methods of test specified in this document provide an instrumental alternative to those specified in
stops: Not at 0.71 cm
ISO 787--16 and ISO 787--17 respectively, avoiding the necessity of visual matching.
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Adjust space between Asian text and numbers
4.2 Coloured and black pigments
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Equal masses of a coloured test pigment p1 and of an agreed
...

PROJET FINAL
Norme
internationale
ISO/TC 256
Méthodes générales d’essai des
Secrétariat: DIN
pigments et matières de charge —
Début de vote:
2026-06-25
Partie 24:
Méthodes photométriques pour la
Vote clos le:
2026-08-20
détermination du pouvoir colorant
relatif des pigments colorés et
du pouvoir diffusant relatif des
pigments blancs
General methods of test for pigments and extenders —
Part 24: Photometric methods for determining the relative tinting
strength of coloured pigments and the relative scattering power
of white pigments
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS
AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À
FOURNIR UNE DOCUMENTATION EXPLICATIVE.
OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
ÉTABLIR S’ILS SONT ACCEPTABLES À DES FINS
INDUSTRIELLES, TECHNOLOGIQUES ET COM-MERCIALES,
AINSI QUE DU POINT DE VUE DES UTILISATEURS, LES
PROJETS DE NORMES
TRAITEMENT PARALLÈLE ISO/CEN
INTERNATIONALES DOIVENT PARFOIS ÊTRE CONSIDÉRÉS
DU POINT DE VUE DE LEUR POSSI BILITÉ DE DEVENIR DES
NORMES POUVANT
SERVIR DE RÉFÉRENCE DANS LA RÉGLEMENTATION
NATIONALE.
Numéro de référence
PROJET FINAL
Norme
internationale
ISO/TC 256
Méthodes générales d’essai des
Secrétariat: DIN
pigments et matières de charge —
Début de vote:
Partie 24: 2026-06-25
Méthodes photométriques pour la
Vote clos le:
2026-08-20
détermination du pouvoir colorant
relatif des pigments colorés et
du pouvoir diffusant relatif des
pigments blancs
General methods of test for pigments and extenders —
Part 24: Photometric methods for determining the relative tinting
strength of coloured pigments and the relative scattering power
of white pigments
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS
AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À
FOURNIR UNE DOCUMENTATION EXPLICATIVE.
DOCUMENT PROTÉGÉ PAR COPYRIGHT
OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
ÉTABLIR S’ILS SONT ACCEPTABLES À DES FINS
© ISO 2026 INDUSTRIELLES, TECHNOLOGIQUES ET COM-MERCIALES,
AINSI QUE DU POINT DE VUE DES UTILISATEURS, LES
Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette
PROJETS DE NORMES
TRAITEMENT PARALLÈLE ISO/CEN
INTERNATIONALES DOIVENT PARFOIS ÊTRE CONSIDÉRÉS
publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,
DU POINT DE VUE DE LEUR POSSI BILITÉ DE DEVENIR DES
y compris la photocopie, ou la diffusion sur l’internet ou sur un intranet, sans autorisation écrite préalable. Une autorisation peut
NORMES POUVANT
être demandée à l’ISO à l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.
SERVIR DE RÉFÉRENCE DANS LA RÉGLEMENTATION
NATIONALE.
ISO copyright office
Case postale 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Genève
Tél.: [phone]
E-mail: [e-mail]
Web: www.iso.org
Publié en Suisse Numéro de référence
ii
Sommaire Page
Avant-propos .iv
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 2
3.1 Termes relatifs aux pigments colorés et noirs.2
3.2 Termes relatifs aux pigments blancs .3
3.3 Termes relatifs à la réflectivité .3
3.4 Termes relatifs au facteur de réflectance .3
4 Principe. 3
4.1 Généralités .3
4.2 Pigments colorés et noirs .4
4.3 Pigments blancs .4
5 Matériel et équipement . 4
6 Appareillage . 5
7 Échantillonnage . 6
8 Mode opératoire . 6
8.1 Détermination du pouvoir colorant relatif .6
8.1.1 Mise en dispersion du pigment à soumettre à essai .6
8.1.2 Mise en dispersion du pigment de référence .7
8.1.3 Préparation des films d’essai .7
8.1.4 Mesure de ϱ ou R .7
∞ ∞
8.2 Détermination du pouvoir diffusant relatif .7
8.2.1 Généralités .7
8.2.2 Mise en dispersion du pigment à soumettre à essai .7
8.2.3 Mise en dispersion du pigment de référence .8
8.2.4 Préparation des films d’essai .8
8.2.5 Mesure de ϱ ou R .8
∞ ∞
9 Expression des résultats . 8
10 Rapport d’essai . 8
Annexe A (informative) Réflectivité et analyse de Kubelka-Munk .10
Bibliographie .11

iii
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux
de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général
confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire
partie du comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (IEC) en ce qui concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d'approbation requis pour les différents types de documents ISO. Le présent document
a été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2
(voir www.iso.org/directives).
L'ISO attire l'attention sur le fait que la mise en application du présent document peut entraîner l'utilisation
d'un ou de plusieurs brevets. L'ISO ne prend pas position quant à la preuve, à la validité et à l'applicabilité de
tout droit de brevet revendiqué à cet égard. À la date de publication du présent document, l'ISO n’avait pas
reçu notification qu'un ou plusieurs brevets pouvaient être nécessaires à sa mise en application. Toutefois,
il y a lieu d'avertir les responsables de la mise en application du présent document que des informations
plus récentes sont susceptibles de figurer dans la base de données de brevets, disponible à l'adresse
www.iso.org/brevets. L'ISO ne saurait être tenue pour responsable de ne pas avoir identifié tout ou partie de
tels droits de brevet.
Les appellations commerciales éventuellement mentionnées dans le présent document sont données pour
information, par souci de commodité, à l'intention des utilisateurs et ne sauraient constituer un engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion de
l'ISO aux principes de l'Organisation mondiale du commerce (OMC) concernant les obstacles techniques au
commerce (OTC), voir le lien suivant: www.iso.org/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 256, Pigments, colorants et matières de
charge, en collaboration avec le comité technique CEN/TC 298, Pigments et matières de charge du Comité
européen de normalisation (CEN), conformément à l'Accord de coopération technique entre l'ISO et le CEN
(Accord de Vienne).
Cette troisième édition annule et remplace la deuxième édition (ISO 787-24:1985) qui a fait l’objet d’une
révision technique.
Les principales modifications sont les suivantes:
— l’introduction a été supprimée;
— les références normatives ont été mises à jour;
— dans l’Article 3, les définitions ont été mises à jour et, si nécessaire, alignées sur l’ISO 18451-1;
— au 3.1.3, “indice d’absorbance” a été remplacé par “indice d'absorption”;
— le paragraphe 4.1 a été ajouté
— au paragraphe 4.2, “K ” a été remplacé par “C “ comme symbole pour le pouvoir colorant relatif;
r rel
— aux paragraphes 4.2 et 8.1.4, la méthode a été ouverte à d’autres critères de pouvoir colorant, y compris
une référence à l’ISO 18314-2;
— la caractéristique “valeur de l’indice au nigromètre” et son exigence de l’Article 5 ont été modifiées en
”
“valeur de noirceur M pour la caractéristique et en “203 à 215” pour l’exigence, et l’ISO 18314-3 a été
Y
ajoutée comme méthode d’essai pour le pigment de noir de carbone (Article 5, Tableau 2);

iv
2 2
— l’exigence de “surface spécifique (BET)” a été modifiée en “25 m /g à 33 m /g” pour le pigment de noir de
carbone (Article 5, Tableau 2);
— l’exigence de la valeur du pH a été modifiée en “6 à 9” pour le pigment de noir de carbone (Article 5,
Tableau 2);
— l’ISO 9277 a été ajoutée comme méthode d’essai pour la surface spécifique (BET) de la silice pyrogénée
(Article 5, Tableau 3);
— au paragraphe 6.3, une référence a été incluse qui décrit la possibilité de mesurer des films de pâte sur
un support mobile sans aucun contact;
— au paragraphe 6.4, des sources lumineuses supplémentaires ont été incluses pour le colorimètre
tristimulus;
— l'Annexe A a été modifiée et subdivisée en A.1 et A.2;
— l'Annexe B a été supprimée;
— une Bibliographie a été ajoutée.
Une liste de toutes les parties de la série ISO 787 se trouve sur le site web de l’ISO.
Il convient que l'utilisateur adresse tout retour d'information ou toute question concernant le présent
document à l'organisme national de normalisation de son pays. Une liste exhaustive desdits organismes se
trouve à l'adresse www.iso.org/members.html.

v
PROJET FINAL Norme internationale ISO/FDIS 787-24:2026(fr)
Méthodes générales d’essai des pigments et matières de
charge —
Partie 24:
Méthodes photométriques pour la détermination du pouvoir
colorant relatif des pigments colorés et du pouvoir diffusant
relatif des pigments blancs
1 Domaine d’application
Le présent document spécifie des méthodes d’essai photométriques pour la comparaison dans le spectre
visible.
a) le pouvoir colorant de deux pigments colorés similaires dispersés dans une résine alkyde sans siccatif;
b) le pouvoir diffusant de deux pigments blancs du même type dispersés dans une résine alkyde sans
siccatif.
Le présent document ne s'applique pas à la comparaison de pigments colorés dont la couleur varie
considérablement en fonction de la réduction.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu'ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l'édition citée s'applique. Pour
les références non datées, la dernière édition du document de référence s'applique (y compris les éventuels
amendements).
ISO 591-1, Pigments de dioxyde de titane pour peintures — Partie 1: Spécifications et méthodes d'essai
ISO 787-2, Méthodes générales d'essai des pigments et matières de charge — Partie 2: Détermination de la
teneur en matière volatile à 105 °C
ISO 787-9, Méthodes générales d’essai des pigments et matières de charge — Partie 9: Détermination du pH
d’une suspension aqueuse
ISO 787-10, Méthodes générales d'essai des pigments et matières de charge — Partie 10: Détermination de la
masse volumique — Méthode utilisant un pycnomètre
ISO 3219 (toutes les parties), Rhéologie
ISO 2114, Plastiques (résines de polyesters) et peintures et vernis (liants) — Détermination de l'indice d'acide
partiel et de l'indice d'acide total
ISO 4629 (toutes les parties), Liants pour peintures et vernis — Détermination de l’indice d’hydroxyle
ISO 4652, Ingrédients de mélange du caoutchouc — Noir de carbone — Détermination de la surface spécifique
par méthodes par adsorption d'azote — Modes opératoires à un point de mesure
ISO 6209, Ingrédients de mélange du caoutchouc — Noir de carbone — Détermination des matières extractibles
par les solvants
ISO 9277, Détermination de l'aire massique (surface spécifique) des solides par adsorption de gaz — Méthode
BET
ISO 15528, Peintures, vernis et matières premières pour peintures et vernis — Échantillonnage
ISO 18314-2, Analyse colorimétrique — Partie 2: Correction de Saunderson, solutions de l'équation de Kubelka-
Munk, pouvoir colorant, profondeur de teinte et pouvoir masquant
ISO 18314-3, Analyse colorimétrique — Partie 3: Indices spéciaux
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions suivants s'appliquent.
L'ISO et l'IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en normalisation,
consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l'adresse https:// www .iso .org/ obp
— IEC Electropedia: disponible à l'adresse https:// www .electropedia .org/
3.1 Termes relatifs aux pigments colorés et noirs
3.1.1
pouvoir colorant
intensité de la couleur
mesure de l’aptitude d’une matière colorante à colorer d’autres matériaux en raison de son pouvoir absorbant
[SOURCE: ISO 18451-1:2019, 3.122]
3.1.2
coefficient d'absorption spectrale
K(λ)
fraction du flux d'un rayonnement incident diffus, de longueur d'onde λ, qui est absorbée par une couche
élémentaire à l'intérieur d'un matériau, divisée par l'épaisseur de la couche (analyse de Kubelka-Munk)
Note 1 à l'article: K(λ) est une mesure du pouvoir colorant (3.1.1) des pigments colorés dans un matériau.
3.1.3
indice d'absorption
K (λ)
p
coefficient d'absorption spectrale (3.1.2) du liant pigmenté divisé par la concentration pigmentaire C :
m
K 

K  

p
C
m
où C est la concentration du pigment exprimée, par exemple, comme le rapport en masses du pigment au
m
liant
3.1.4
pouvoir colorant relatif
intensité relative de la couleur
C
rel
rapport, exprimé en pourcentage, entre le pouvoircolorant (3.1.1) de la matière colorante en essai et le
pouvoir colorant (3.1.1) d'une matière colorante de référence
[SOURCE: ISO 18451-1:2019, 3.105, modifié — le symbole C a été ajouté.]
rel
3.2 Termes relatifs aux pigments blancs
3.2.1
pouvoir diffusant
aptitude d'un milieu pigmenté à diffuser partiellement la lumière incidente
3.2.2
coefficient de diffusion spectrale
S(λ)
fraction du flux de rayonnement spectral, de longueur d’onde λ, renvoyée à l’extérieur par une couche
élémentaire située à l’intérieur d’un matériau illuminé de l’extérieur, divisée par le produit de l’épaisseur de
la couche par la différence de grandeur du flux dans les deux directions au travers de la couche (analyse de
Kubelka-Munk)
Note 1 à l'article: S(λ) est une mesure du pouvoir diffusant (3.2.1) des colorants blancs incorporés dans un matériau et
s’exprime comme l’inverse de l’épaisseur du film.
3.2.3
indice de diffusion
S (λ)
p
coefficient de diffusion spectrale (3.2.2) du liant pigmenté divisé par la concentration pigmentaire C :
m
S 

S  

p
C
m
3.2.4
pouvoir diffusant relatif
rapport, exprimé en pourcentage, entre le pouvoir diffusant du pigment blanc en essai et le pouvoir diffusant
d'un pigment blanc de référence
[SOURCE: ISO 18451-1:2019, 3.104, modifié — dans la définition, “indice de diffusion” a été remplacé deux
fois par “pouvoir diffusant”.]
3.3 Termes relatifs à la réflectivité
3.3.1
réflectivité
ϱ
∞
facteur de réflexion d’une pâte ou d’un feuil dont l'épaisseur est telle qu’une augmentation de l’épaisseur ne
modifie pas le facteur de réf
...