ICS 87.060.10  
 
Reference number  
DRS 495 -1: 2022 
© RSB 2022  
  
 RWANDA 
STANDARD  DRS  
495-1  
 
First edition  
2022 -mm-dd 
 
Organic pigments for paints  — 
Specification  — 
Part 1: 
Azo pigments  
   
DRS 4 95-1: 2022  
©RSB 2022  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2022  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
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Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 495 -1: 2022  
iii                ©RSB 2022  - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ............................  iv 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  2 
4 Requirements  ................................ ................................ ................................ ................................ .........  2 
4.1 General requirements  ................................ ................................ ................................ ...........................  2 
4.2 Specific requirements  ................................ ................................ ................................ ...........................  2 
5 Packaging and labelling ................................ ................................ ................................ ........................  3 
5.1 Packaging  ................................ ................................ ................................ ................................ ...............  3 
5.2 Labelling  ................................ ................................ ................................ ................................ .................  3 
6 Sampling  ................................ ................................ ................................ ................................ ................  4 
Annex  A (normative)  Determination of sulphated ash  ................................ ................................ ..................  5 
A.1 Procedure  ................................ ................................ ................................ ................................ ...............  5 
A.2 Calculation  ................................ ................................ ................................ ................................ .............  5 
Annex  B (normative)  Determination of resistance to acid, alkali and lime  ................................ .................  6 
B.1 Outline of the method  ................................ ................................ ................................ ...........................  6 
B.2 Reag ents ................................ ................................ ................................ ................................ ................  6 
B.3 Procedure  ................................ ................................ ................................ ................................ ...............  6 
 DRS 4 95-1: 2022  
©RSB 2022  - All rights reserved                  iv 
 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by Rwanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and a pplication of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards 
adopted by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standar ds. 
DRS  495-1 was prepared by Technical Committee RSB/TC 056, Paints, Varnishes, Adhesives and Related 
Products . 
In the preparation of this standard, reference was made to the following standard:  
IS 3574 : Specification for organic pigments for paints – Part 1: Azo Pigments (Toluidine red; chlorinated p-
Nitroani line red; arylamide yellows; and para red)  
The assistance de rived from the above source is hereby acknowledged with thanks.  
DRS 495  consists of the f ollowing parts, under the general title Organic pigments for paints  — Specification : 
⎯ Part 1: Azo pigments  
⎯ Part 2: Phthalocyanines  
Committee membership  
The following organizations were represented on the Technical Committee on Paint, Varnishes, Adhesives 
and related Products  (RSB/TC 056) in the preparation of this standard.  
University of Rwanda/College of Sciences and Technology (UR/CST)  
University of Rwa nda/College of Education (UR/CE)  
EARTHENABLE  
Standards for Sustainability (SfS)  
AMACO Paints  
Rwanda Inspectorate, Competition and Consumer Protection Authority (RICA)  DRS 495 -1: 2022  
v                ©RSB 2022  - All rights reserved  
 REX Paints  
Star Construction and Consultancy Ltd  
IPRC Kigali  
MEI Paints  
Rwanda  Standards Board  (RSB) – Secretariat  DRS 4 95-1: 2022  
©RSB 2022  - All rights reserved                  vi 
 Introduction   
Among the most important organic pigments used in paint industry are toluidine re d, chlorinated p-nitroaniline 
red (commercially known as signal red or permanent red), arylamide yellow G and 10 G (commercially known 
as fast yellow or hansa yellow) and to some extent para red. Dinitro -aniline red (permanent orange) is not 
included as the production of this pigment has been prohibited. The colour index number of these pigments 
are as follows:  
i) Toluid ine red – colour index No 12120; C.I. pigment red 3.  
ii) Chlorinated p-nitroaniline red – colour index No 12085; C.I. pigment red 4.  
iii) Arylamide yellow G – colour index No 11680; C.I. pigment yellow 1.  
iv) Arylamide yellow 10 G – colour index No 11710; C.I. pigment yellow 3.  
v) Para red – colour index No 12070; C.I. pigment red 1.  
Toluidine reds may differ in mass tone. The most office red colour characteristically produced by this pigment 
is obtained by using either a single pigment or more often by a blend of two or m ore pigments. The blending of 
toluidine reds of varying mass tones is usually necessary in ord er to get a  close match to Indian Standard 
Colour No 538 of IS 5 -1961 . 
Unlike toluidine reds, chlorinated p-nitroaniline red is usually produced in order to get a  close match to IS 
Colour No 537 of IS 5 -1961, directly without further bending. Sometimes, manufacturers of chlorinated p-
nitroaniline red in two mass tones, namely one a little lighter and the other a little deeper in colour to IS Colour 
No 537 of IS 5 -1961. A judicious blending of these two results in a close match to the standard colour desired.  
Arylamide yellow G and 10 G differ in mass tones ( G denotes pure yellow and 10 G denotes greenish yellow). 
A suitable blend of arylamide yellow G and 10 G will produce arylamide yellow 3 G and arylamide yellow  7G. 
Para red is usually produced only in one mass tone and used in cheaper type of paints on account of its lower 
cost.  
 
 DRS  495-1: 2022  
1                ©RSB 2022  - All rights reserved  
 Organic pigments for paints  — Specification  — Part 1: Azo Pigments  
1 Scope   
This Draft  Rwanda Standard  specifies the requirements, sampling and test methods for five (5) organic 
pigments, namely, toluidine red, chlorinated p-nitroaniline red, arylamide yellow G and 10 G and para red 
used in paint industry.  
2 Normative references   
The followin g 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 18451 -1, Pigments, dyestuffs and extenders — Terminology — Part 1: General terms  
ISO 18451 -2, Pigments, dyestuffs and extenders — Terminology — Part 2: Classification of colouring 
materials according to colouristic and chemical aspects  
ISO 787 -7, General methods of test for pigments and extenders — Part 7: Determination of residue on sieve 
— Water method — Manual procedure  
ISO 787 -2, General methods of test for pigments and extenders — Part 2: Determinati on of matter volatile at 
105 degrees C  
ISO 787 -3, General methods of test for pigments and extenders — Part 3: Determination of matter soluble in 
water — Hot extraction method  
ISO 787 -5, General methods of test for pigments and extenders — Part 5: Determin ation of oil absorption 
value  
ISO 787 -25, General methods of test for pigments and extenders — Part 25: Comparison of the colour, in full -
shade systems, of white, black and coloured pigments — Colorimetric method  
ISO 787 -16, General methods of test for pig ments and extenders — Part 16: Determination of relative tinting 
strength (or equivalent colouring value) and colour on reduction of coloured pigments — Visual comparison 
method  
ISO 787 -15, General methods of test for pigments and extenders — Part 15: Comp arison of resistance to light 
of coloured pigments of similar types  
ISO 787 -22, General methods of test for pigments and extenders — Part 22: Comparison of resistance to 
bleeding of pigments   
©RSB 2022  - All rights reserved                  2 
 ISO 787 -21, General methods of test for pigments and extenders — Part 21: Comparison of heat stability of 
pigments using a stoving medium  
RS OIML R 87 , Quantity of product in pre -packages  
ISO 15528 , Paints, varnishes and raw materials for paints and varnishes — Sampling  
3 Terms and definitions   
For the purposes of this standard, the terms and definitions given in ISO 18451 -1, ISO 18451 -2 and the 
following apply.  
3.1 
term  
text of the definition  
4 Requirements  
4.1 General requirements  
4.1.1  The pigment shall be in the form of a fine, dry, soft powder or in such a condition that it can be readily 
reduced to the powder form by crushing under a palette knife, without grinding action  
4.1.2  The pigment shall be free from grit.  
4.2 Specific requirements  
The pigments shall comply with the requirements giv en in table 1 when tested in accordance with the methods 
prescribed therein.  
Table 1 — Specific requirements for Azo Pigments  
S/N Parameters  Requirements  Test methods  
1 Residue on sieve, % by mass, max.  0.5 ISO 787 -7 
2 Sulphated ash, % by 
mass, max.  Toluidine red  2.5 
Annex A  Chlorinated p-
nitroaniline red  2.5 
Arylamide yellow G  3.5 
Arylamide yellow 10 G  3.5 
Para red  10.0 
3 Matter volatile at 100 ˚C, % by mass, max.  1.0 ISO 787 -2 
4 Matter soluble in water, % by mass, max.  1.0 ISO 787-3 
5 Oil absorption values 1 Toluidine red  35 – 65  ISO 787 -5 DRS  495-1: 2022  
3                ©RSB 2022  - All rights reserved  
 Chlorinated p-
nitroaniline red  45 – 65  
Arylamide yellow G  40 – 60  
Arylamide yellow 10 G  40 – 60  
Para red  35 – 65  
6 Colour  Close match to the 
approved sample  ISO 787 -25 
7 Staining power and colour on reduction  Do ISO 787 -16 
8 Fastness to light  Not inferior to the 
approved sample  ISO 787 -15 
10 Bleeding  Do  ISO 787 -22 
11 Heat stability  Do  ISO 787 -21 
12 Resistance to acids and alkalis  Do  Annex B  
1 The value of oil absorption shall be within ± 5% of the approved sample, if any.  
 
5 Packaging and labelling  
5.1 Packaging  
6.1.1  The pigment  shall be packaged in a suitable container that prevents it from deterioration during 
storage, transportation and normal handling.  
6.1.2  The quantity of product packaged in a container shall be in accordance with the requirements of RS 
OIML R 87.  
5.2 Labelling  
6.2.1  Each container shall be labell ed legibly and indelibly with the following  information in any of the three 
languages officially accepted in the Republic of Rwanda namely: Kinyarwanda, French and English:  
a) name of the product ; 
b) name and address of the m anufacturer and/or registered trader mark;  
c) net content ; 
d) organic/inorganic colouring matter, % by mass, if added;  
e) batch number  
f) manufacture and expiry d ates;  
©RSB 2022  - All rights reserved                  4 
 g) instructions for use and disposal;  
h) special precautions, if any; and  
i) storage condition  
6 Sampling  
Sampl ing shall be done in accordance with RS ISO 15528.  
 DRS  495-1: 2022  
5                ©RSB 2022  - All rights reserved  
 Annex  A 
(normative)  
 
Determination of sulphated ash  
A.1 Procedure  
Cool a previously ignited and weighed crucible in a desiccator and weigh accurately into it about 2 g of the test 
sample. Heat gently i the flame of a Bunsen burner until burning and charring is complete. Moisten with a few 
drops of concentrated sulphuric acid and heat gently until fuming ceases. Ignite strongly and cool in a 
desiccator. Repeat ignition until constant mass is obtained.  
A.2 Calculation  
Matter volatile, % by mass =100(𝑀1−𝑀2)
𝑀1 
 
   
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 Annex  B 
(normative)  
 
Determination of resistance to acid, alkali and lime  
B.1 Outline of the method  
Resistance to acid, alkali and lime is determined by finding out the degree of bleeding of the solutions 
prepared from material under test and the approved sample in hydrochloric acid, sodium hydroxide and 
calcium hydroxide solution respectively. Additionally, the treated pigment is washed, dried and tested against 
pigment for full colour and reduct ion. 
B.2 Reagents  
B.2.1  Standard Hydrochloric Acid  – 0.5 N  
B.2.2  Standard Sodium Hydroxide Solution  – 0.25  
B.2.3  Calcium Hydroxide Solution  – 10% 
B.3 Procedure  
B.3.1  Resistance to acid  – Take about 1g of the pigment in a 100 -mL flask and shake with about 50 mL of  
standard hydrochloric acid. Allow the contents to stand for one hour. In another flask treat an equal quantity of 
the approved sample in a similar manner. Note the colour change in the supernatant liquid of the material 
under test as compared with that of  the approved sample. Wash the pigment free from acid, filter and dry in an 
oven at 100 ± 2 ˚C. Determine the change in colour and staining power of the pigment. Compare the change 
in the test sample with that obtained in the case of the approved sample, w hen similarly treated and tested.  
B.3.2  Resistance to lime  – Repeat the above test (see B.3.1) but using calcium hydroxide solution in 
place of standard hydrochloric acid.  
B.3.3  Resistance to alkali  – Repeat the above test (see B.3.1) but using standard so dium hydroxide 
solution in place of hydrochloric acid.  
  
 DRS  495-1: 2022  
7                ©RSB 2022  - All rights reserved  
 Bibliography  
[1] IS 3493 , Method of sampling and test for organic pigments for paints , 1978  
 
 DRS  495-1: 2022  
 
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