ICS 71.100.40  
 
Reference number  
DRS 88: 2021  
© RSB 2021  
  
 RWANDA 
STANDARD  DRS 
88 
 
Second edition  
2021 -mm-dd 
 
Washing bars  — Specification  
   
DRS 88: 2021  
©RSB 20 21 - 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 2021 
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. 
Requests for permission to reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 88: 2021  
iii                ©RSB 2021  - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 Requirements  ................................ ................................ ................................ ................................  2 
4.1 Composition  ................................ ................................ ................................ ................................ .. 2 
4.2 General requirements  ................................ ................................ ................................ ..................  2 
4.3 Performance requirements  ................................ ................................ ................................ ..........  2 
5 Pack aging and labelling ................................ ................................ ................................ ...............  3 
5.1 Packaging  ................................ ................................ ................................ ................................ ...... 3 
5.2 Labelling  ................................ ................................ ................................ ................................ ........  3 
6 Sampling  ................................ ................................ ................................ ................................ ....... 4 
6.1 General  ................................ ................................ ................................ ................................ ..........  4 
6.2 Sample for inspection  ................................ ................................ ................................ ..................  4 
6.3 Sample for testing  ................................ ................................ ................................ ........................  4 
Annex  A (normative)  Permitted structuring and processing aids  ................................ ......................  5 
Annex  B (normative)  Determination of cleaning index  ................................ ................................ ........  7 
B.1 Principle and instrumentation  ................................ ................................ ................................ ..... 7 
B.2 Sample solutions  ................................ ................................ ................................ ..........................  8 
Annex  C (normative)  Determination of Lather volume  ................................ ................................ .........  9 
C.1 Principle  ................................ ................................ ................................ ................................ ........  9 
C.2 Apparatus  ................................ ................................ ................................ ................................ ...... 9 
C.3 Sodium lauryl sulphate solution  ................................ ................................ ...............................  10 
C.4 Sample preparation  ................................ ................................ ................................ ....................  10 
C.5 Lather  measurement  ................................ ................................ ................................ ..................  10 
C.6 Notes for guidance  ................................ ................................ ................................ .....................  11 
Annex  D (normative)  Determination of the potential wear  ................................ ................................ . 12 
D.1 Principle  ................................ ................................ ................................ ................................ ...... 12 
D.2 Apparatus/Chemic als ................................ ................................ ................................ .................  12 
D.3 Bar preparation  ................................ ................................ ................................ ...........................  13 
D.4 Test procedure  ................................ ................................ ................................ ............................  13 
Annex  E (normative)  Determination of the potential mush  ................................ ................................  15 
E.1 Principle  ................................ ................................ ................................ ................................ ...... 15 
E.2 Equipmen t ................................ ................................ ................................ ................................ ... 15 
E.3 Bar preparation  ................................ ................................ ................................ ...........................  15 
E.4 Test procedure  ................................ ................................ ................................ ............................  16 
Annex  F (normative)  Test for freedom from grit  ................................ ................................ .................  17 
F.1 Outline of the method  ................................ ................................ ................................ ................  17 
F.2 Procedure  ................................ ................................ ................................ ................................ .... 17 
 DRS 88: 2021  
©RSB 20 21 - All rights reserved                  iv 
 Foreword   
Rwanda Standard s are prepared  by Techn ical Committees and approved by R wanda 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 application 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 Standards.  
DRS 88 was prepared by Technical Commi ttee RSB/TC 42, Surface Active Agents . 
In the preparation of this standard, reference was made to the following standard:  
1) DARS 1461 : Washing bars (Performance -based) — Specification  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second edition cancels and replaces the first edition (RS  88: 2015 ), of which has been technically revised.  
 
Committee membership  
The following organizations were represented on the Technical Committee on Surface Active Agents  (RSB/TC 
42) in the preparation of this standard.  
Paragraph of p articipants  
 
Rwanda  Standards Board  (RSB) – Secretariat  DRS 88: 2021  
v                ©RSB 2021  - All rights reserved  
 Introduction   
The available  Standard specification for laundry soaps is based on composition. The major concern is that the 
present compositional standards based primarily on the total fatty matter (TFM) do not necessarily reflect the 
performance of laundry soaps, and it is a limiti ng factor to the application of the latest technological 
developments.  
The latest technological applications in soap design and processing yield products that are different in structure, 
texture, performance and value. They are therefore not fully covered by the current compositional based 
standards. This therefore necessitates that the value and performance benefits of the technology applied be 
valued and appreciated in a performance based standard.  
The performance of soaps depends more on the type/nature of fatty matter present than the total fatty matter in 
soap. For example, the solubility of soap depends on the characteristics of the fatty acid such as chain length, 
level of unsaturation and on the type of cation, besides the processing parameters.  
The main aim of introducing the washing bar standard as a category is therefore to develop standards which 
reflect the trends in the latest technological developments while ensuring the performance and safety of the 
product to the consumer. This shall in parti cular facilitate use of broad spectrum saponification surfactants and 
structuring aids, some of which are locally available. These shall substitute a significant ration of oils, most of 
which are imported and expensive and shall hence boost the country’s e conomy.  
The importance in use criteria for washing bars shall be performance embodied in safety, cleaning and 
economy. With regard to safety, it is important to guard against the removal of the beneficial skin lipids at the 
washing bar and over -cleaning re sulting in defatting of the skin during washing. This shall be ensured in the 
proposed standard by allowing only such surfactants and structuring aids which have a history of safe use in 
washing products. A list of the proposed surfactants and structuring aids is given in Annex F. Other surface 
active agents may be added to the list in a future revision if there is adequate evidence of their safety.  
The cleaning index and lather volume requirements are intended to ensure the presence of adequate types and 
levels of surfactants in the washing bar for cleaning. The lather test is designed to take into account dissolution 
of the bar and subsequent lather generation. The mush and rate of wear tests cover the aspect of economy.  
 
 DRS 88: 202 1 
1                ©RSB 2021  - All rights reserved  
 Washing bars  — Specification  
1 Scope   
This Draft Rwanda Standard specifies  requirements, sampling and test methods for washing bars . 
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 e dition  cited applies. For undated references, the 
latest edition of the referenced document (including any amendments) applies.  
ISO 456, Surface active agents — Analysis of soaps — Determination of free caustic alkali  
 
ISO 457, Soaps — Determination of chloride content — Titrimetric method  
 
ISO 672 , Soaps — Determination of moisture and volatile matter content — Oven method  
 
ISO 673, Soaps — Determination of content of ethanol -insoluble matter  
 
ISO 684, Analysis of soaps — Determination of total free alk ali 
 
ISO 685, Analysis of soaps — Determination of total alkali content and total fatty matter content  
ISO 862, Surface active agents — Vocabulary  
ISO 8212, Soaps and detergents — Techniques of sampling during manufacture  
 
ISO 6839 , Anionic surface active agents — Determination of solubility in water  
RS EAS 377, Cosmetics and Cosmetic Products (all parts)  
3 Terms and definitions   
For the purposes of this standard, the terms and definitions given in ISO 862 and the following apply.  
3.1 
washing bar  
bar processed in a manner so as to meet performance requirements as in 3.4. They are for household washing 
purposes, and primarily have well saponified fatty matter, structurants, preservatives and moisture. The y may 
also contain suitable quantities of co louring matter, perfume, pacifiers and optical brightening agents.  
  
©RSB 20 21 - All rights reserved                  2 
 4 Requirements  
4.1 Composition  
4.1.1  The product shall be made of fatty acids, fatty acid ester sulphonates, fatty alkanolomides, fatty alcohol 
ethoxylates, fatty isothionatese, alpha olefin sul lphonates, alcohol sulphonates and any such proven saponification 
surfactants.  
4.1.2  In addition to suitable surfactants, washing bars shall contain other ingredients such as electrolytes, bar 
structuring processing aids, permitted antioxidants and humecta nts. For guidance, a list of bar structuring aids is 
given in Annex A. 
4.2 General requirements  
4.1.1  The product shall be in the form of bars or tablets.  
4.1.2  The colour of the product shall be uniform, except for multi -coloured bars or tablets.  
 
4.1.3  The product shall not be harmful to skin.  
 
4.1.5  They may contain suitable quantities of colouring matter, perfume, opacifiers and optical brightening 
agents.  
4.1.6  The product shall not contain any materials prohibited and all substances used shall comply wi th the 
requirements of all parts of RS EAS 377  
4.3 Specific requirements  
The product shall comply with the specific requirements given in table 1 . 
Table 1 — Specific  requirements of washing bars  
S/N Parameter  Requirement  Test method  
(i) Cleaning index, max.  2.0 Annex B 
(ii) Lather volume mL, min.  200 Annex C 
(iii) Wear, g/m, max.  1.5 Annex D 
(iv) Mush g/30 cm2, max.  10 Annex E 
(v) Free caustic alkali as NaOH, % by 
weight, max.  0.4 ISO 456  
(vi) Grittiness  To pass test  Annex F 
 DRS 88: 202 1 
3                ©RSB 2021  - All rights reserved  
 5 Packaging and labelling  
5.1 Packaging  
A number bars  shall be packaged in suitable box that could ensure integrity of the product during handling, 
storage and transportation . 
5.2 Labelling  
5.2.1  On each of the primary wrapper/box of washing bars and/or on each package shall be marked wit h the 
following particulars:  
a) Name of the product as  ‘Washing Bar’;  
b) manufacturer’s name and physical address and trade mark if any;  
NOTE  The name, physical address of the distributor/supplier may be added as required.  
c) Net weight   
 
d) batch number or code number  
 
e) date of manufacture and expiry date or best before date ;  
f) On the box or the package containing the cakes shall be marked the number of cakes contained therein;  
5.2.2  Unwrapped Washing  bars   
Each unwrapped washing bar  shall be marked legibly and ind elibly with the following particulars:  
a) Name of the product;  
b) The word “Washing bar”; and  
c) Nominal weight of the bar.  
5.2.3  Cartons/Boxes/ Other packages : 
a) the words ‘ washing bar ; 
b) manufacturer’s name and physical address  and trade mark if any;  
c) batch number or code number;  
d) number of bars or cakes contained in the package;  
e) date of manufacture and best before date;  
f) country of origin , if different from manufacturer address   
©RSB 20 21 - All rights reserved                  4 
  
6 Sampling  
6.1 General  
When no information concerning the implementation of quality control or testing during manufacture is available, 
the following sampling procedure shall be applied to determine whether a lot submitted for inspection and testing 
complies with the requirements of the standard. The samples so taken shall be deemed to represent the  lot for 
the respective properties. The sampling procedure shall also be used for adjudication in cases of dispute.  
6.2 Sample for inspection  
Draw at random from the lot  
a) five containers if the lot is packed in containers of net mass not exceeding 5 kg, and  
b) three containers if the lot is packed in containers of net mass greater than 5 kg.  
6.3 Sample for testing  
6.3.1 From the containers , take at random enough soap to provide a laboratory sample of total mass at least 
2 kg (take equal quantities of soap from all cont ainers).  
6.3.2 Place the laboratory sample in clean, dry, air -tight glass or plastics containers clearly marked with the 
manufacturer's name or trade mark, the batch identification, and the date of sampling.  
6.3.3 In the case of unwrapped soap, take the sa mple bars or tablets (as relevant) from the centre of the 
container.  
 DRS 88: 202 1 
5                ©RSB 2021  - All rights reserved  
 Annex  A 
(normative)  
 
Permitted structuring and processing aids  
Following is a list of structuring and processing aids (excluding colouring matter, perfume, preservatives, 
opacifiers, and optica l brightening agents) that shall generally be used in washing bars.  
g) Starch and derivatives  
h) Cellulose and derivatives  
i) Mannitol  
j) Dextrin  
k) Kaolin  
l) Talc 
m) Bentonite  
n) Calcite/ CaCO 3 
o) Borax  
p) Soda ash  
q) Vegetable/animal fatty acid  
r) Silicates  
s) Phosphates  
t) Sodium chloride  
u) Sodium sulphate  
v) Dolomite  
w) Fatty alcohol  
x) Fatty acid ethanolamide   
©RSB 20 21 - All rights reserved                  6 
 y) Diethylene glycol monostearate  
z) Paraffins  
aa) Polyoxyethylene glycol  
Glycerol monostearates  
New structuring and processing aids shall be added following clearance by the relevant authorities.  
 
  DRS 88: 202 1 
7                ©RSB 2021  - All rights reserved  
 Annex  B 
(normative)  
 
Determination of cleaning index  
B.1 Principle and instrumentation  
The cleaning index expresses the potential of the washing bar to lift off pre -defined stain from a known fabric under 
defined conditions.  
 
The ‘Cleaning Index’ is a ratio of the surface tension of clean water to the difference between the surface tension of 
a standard washing bar solution in which a defined stained cloth is soaked for a defined time; and the surface 
tension of the standard concentration of the washing bar (deterge nt) in water.  
 
Nu Nuoy Tensiometer (Cambridge Instrument Company Ltd.) shall be used to determine the surface tension (or 
any such suitable surface tension measuring equipment).  
In this set up, a platinum iridium ring on the surface of the liquid is suppor ted by a stir -up attached to the beam of 
the torsion balance.  The ring is pricked upwards from the liquid by turning the torsion wire, thus applying a force 
which is known from calibration of the instrument for an idealized system. The force necessary to separate  the ring 
from the liquid is equal to 4 Ry, where R is the mean radius of the ring, i.e.  
 
Figure A.1 — Platinum iridium ring  
Doubling of the perimeter arises from the fact that there are two boundary lines between liquid and wire, one on the 
outside and one on the inside of the ring. The shape of the liquid held up influences the force necessary for breaking 
away.  
 
The shape is a function of R3/V and R/r where v is the volume of the liquid held up and r is the radiu s of the wire . 
The surface tension is thus given by the equation:  
 
Y  =   
F
Rf
4Π  
 
where,   
©RSB 20 21 - All rights reserved                  8 
  
 
f   =   maximum force registered on a torsion balance scale;  
 
 
F   =  correction  factor due to shape of liquid held up and the ring dimensions.  
 
Over extreme variations of R3/N and R/r, F varies between about 0.75 and 1.02. In ordinary cases it is close to 1.  
B.2 Sample solutions  
B.2.1  Preparation of stained cloth  — The staining solution consists of ethyl acetate analytical grade engine 
oil in the volume ratio of 4:1.  
NOTE  This method was developed using Caltex motor oil SAE 40.  
Pieces of cotton cloth measuring 4 cm x 4 cm are then stained being soaked in the staining solution for 60 minutes 
(ensure uniform staining by continuously swirling the beaker). The cloth pieces are then dried in an oven at 80 ºC 
for 48 hours.  
B.2.2  Detergent solutions  — These are prepared by dissolving 1.0 g of each bar sample in 300 mL of hot water 
(ordinary tap water) and left to stand for 21 hours.  
 
Surface tension measurements or these solutions are then recorded to give yDet.  
 
Stained cloth pieces prepared in ( B.2.1) are then soaked in 50 mL of the washing bar solution and let to stay for 21 
hours.  
 
The surface tension of the soiled solution is then determined to give yDet/Stain.  
 
The clearing index (C.l) is then computed from the expression:  
 
C.I = 
1
/2010   Det Stain Det y yyH  
 
or 
 
C.I = 
1 210   yyHO  
 
where,  
OHy2
  =   the surface tension pure water; and  
y
     =  
Stain/Dety  - 
Dety . 
 DRS 88: 202 1 
9                ©RSB 2021  - All rights reserved  
 Annex  C 
(normative)  
 
Determination of Lather volume  
C.1 Principle  
A domestic kitchen blender is adjusted to deliver 600 ± 100 mL of lather in 60  seconds from a 1 per cent solution 
of sodium lauryl sulphate in 300 ppm calcium hard water at 25 ºC.  
The bar is transformed into uniform 2 mm diameter noddles  by hand extrusion through a perforated plate. 100 mL 
of 300 ppm calcium hard water at 25 ºC and 5 grams of bar noodles are agitated in the adjusted kitchen blender for 
60 seconds and the lather volume is measured. The bar lather is normalized to a volume of 600 mL from the SLS 
solution tested in the same blender.  
C.2 Apparatus  
C.2.1  Kitchen food blender  — Hamilton beach commercial bar mixer with a low speed of 14 000 rpm, high 
speed of 18 000 RPM. It shall be operated at a speed which shall deliver a lather vo lume of 600 ± 100 mL from a 
standard solution on sodium lauryl sulphate defined in Clause C.3. The test procedure is described in C.5. 
C.2.2  Bar extruder  — The bar extruder consists of a block of metal 10 cm x 10 cm x 50 cm drilled centrally 
through the lo nger axis with a 25 mm diameter hole. The hole is threaded and a matching threaded bolt is provided. 
A plate with well separated 2 mm diameter holes is bolted to one end of the metal block.  
Any device which shall extrude bar through a plate with 2 mm diame ter holes is quite suitable. The equipment 
consists of a block of metal 10 cm x 10 cm x 5 0 cm drilled centrally through the longer axis with a 25 mm diameter 
hole. The hole is threaded and a matching threaded bolt is provided.  Plate with well separated 2 mm diameter 
holes is bolted to one end of the metal block.  
Materials of construction, screw thread and dimensions other than the end plate holes are not critical. To ease 
cleaning of the equipment and to make extrusion easier, the end plate shall not be to o thick. A 3 mm thickness plate 
is sufficiently robust.  
For use, the device is conveniently clamped vertically in a bench vice and the bolt is turned by hand, or for higher 
time or aged products with a spanner or bar. The lower end is encased in a plastic bag held in place by elastic or 
tape to collect the bar noodles extruding from the end plate.  
B.2.3  Other equipment/chemicals  
 A coarse cheese grater;  
 Measuring cylinder 1 000 mL;  
 Volume equipment/balance for hard water preparation;  
 Sodium laurly sulphate, that shall have minimum 99 per cent purity, C 12 compounds by GLC shall be a 
minimum of 98 per cent.  
The impurity level shall be as given in Table B.1 below.   
©RSB 20 21 - All rights reserved                  10 
 Table B.1 — Impurity level  
Maximum limit of impurities  Per cent  
Loss on drying at 110 ºC  1 
Acidity or alkalinity  0.5 mL N %  
Chloride  0.03 
Phosphate as P O4 0.001  
Copper as Cu  0.0005  
Iron as Fe  0.0001  
Lead as Pb  0.0005  
C.3 Sodium lauryl sulphate solution  
Prepare a 1 per cent solution of sodium lauryl sulphate (SLS) in 300 ppm calcium hardness water.  Solution more 
than 1 week old shall not be used.  
C.4 Sample preparation  
C.4.1  The requirement is for a lather measurement on three samples from each of three bars taken during the 
sampling procedure  6. 
C.4.2  Approximately 100 g of each bar is coarsely grated with a kitchen cheese grater.  The gratings are quickly 
mixed by hand and then transferred to a labelled container which is closed to  prevent moisture loss.  
C.4.3  Grated bar from the sample is introduced into the threaded barrel of the extruder desc ribed above. 
Sufficient bar shall be used to ensure production of at least 20 grams of coherent noodles by the procedure 
described in Clause C.2. The noodles from each bar shall be divided into 3 equal parts for the subsequent lather 
tests.  
C.5 Lather measurement  
C.5.1  All test shall be performed at 25 ºC ± 2 ºC.  
C.5.2  Lather from the standard SLS solution  — 100 mL of the standard SLS solution is poured into the jar 
of the kitchen food blender, the jar is covered and the blender is run for exactly 60 se conds.  Immediately the blender 
jar is inverted over a 1 litre measuring cylinder and the liquid and foam are allowed to drain.  A large plastic spatula 
or ruler shall be used to scoop residual foam from the jar into the measuring cylinder.  The top of the  foam is levelled 
off and the total volume of material in the cylinder is taken as the lather volume value, i.e. with no allowance for any 
liquid volume which may separate from the foam.  
If the foam volume is not 600 ± 100 mL, adjust the mixer speed and re peat the test until a foam volume in this range 
is achieved.  
Once the blender speed setting is confirmed, it shall be used for all subsequent tests on SLS solution and bar 
samples.  DRS 88: 202 1 
11                ©RSB 2021  - All rights reserved  
 C.5.3  Lather from bar sample  — Pour 100 mL of 300 ppm calcium hardness wate r into the blender jar.  Add 5 
grams of extruded bar noodles prepared as in B.4.  Cover the jar and operate the blender for exactly 60 seconds at 
the speed identified in B.5.2  as giving 600 ± 100 mL of foam with the standard SLS solution.  Quickly pour the foam 
and any residual liquid into a 500 mL or 1 litre measuring cylinder.  
C.6 Notes for guidance  
NOTE 1  Temperature  
Although an ambient temperature and equipment shall be maintai ned at 25 ± 2 ºC, this is not always easy to achieve. 
It is essential to measure the temperature of the SLS or bar foam after the volume measurement. If the temperature 
recorded is outside the range 25 ± 2 ºC, the test shall be repeated with the starting S LS solution or water temperature 
adjusted so that the final temperature of the foam is within the specified range  
NOTE 2  Number of lather volume measurements  
For each bar type to be tested, three (3) measurements are made on the noodles produced from three  (3) bars of 
the type.  
NOTE 3  Sequence of lather tests  
Once the kitchen food blender is established as delivering 600 ± 100 mL, the SLS solution and noodles prepared 
from each of 3 bars of the type the sequence of testing shall be as follows:  
Lather volume  SLS;  
Lather volume on noodles from bar 1;  
Normalize the bar lather to an SLS volume of 600 mL  = V1/1;  
 
Lather volume SLS;  
Lather volume on bar noodles from bar 1;  
Normalize the bar lather to an SLS volume of 600 mL  =  V2/1;  
 
Lather volume SLS,  
Lather vo lume on bar noodles from bar 1;  
Normalize the bar lather to an SLS volume of 600 mL  =  V3/1.  
The average of V1 - 3/1 volumes is the sample value for bar 1.  
This procedure is continued for bars 2 and 3 taken from the same sample lot.  The average of the three sample 
values shall be reported as the lot value.  
NOTE 4  Normalizing lather volumes  
Normalized bar volume  =  Actual bar volume   X   
volume SLS Actual600   
©RSB 20 21 - All rights reserved                  12 
 Annex  D 
(normative)  
 
Determination of the potential wear  
D.1 Principle  
A bar of fixed dimensions cut fro m the product is first preconditioned by allowing it to stand on a damp cloth. The 
bar is held in a weighted holder, and is moved across a wetted fabric in a prescribed manner. The weight loss from 
the bar during rubbing is measured and expressed as grams lost per 10 metres of rubbed fabric.  
For each bar type to be tested, three (3) consecutive wear measurements are made on three (3) bars of the 
type.  If the bar size is too small to allow three consecutive wear measurements on each sample, then nine (9) 
individual samples of each product shall be tested.  
D.2 Apparatus/Chemicals  
D.2.1  For bar preparation  
(a) Coarse kitchen cheese grater;  
(b) Sharp thin bladed knife;  
(c) A weighted bar holder.  
The holder and the weight shall be fixed together or shall separate. The total weight of the holder and weight shall 
be standardized to 110 ± 25 grams.  
D.2.2  For the test procedure  
(a) De-sized cotton cloth with a weave of close to 32 by 32 threads per cm. Cut to pieces 61 cm x 39 cm.  
(b) A tray of non corrodible  metal or rigid plastic sized to accommodate the 61 cm x 39 cm test cloths.  
(c) A number of small flat bottomed trays of non corrodible metal or plastic (bar dishes) equal to the number of 
samples to be tested.  
(d) De-sized cotton cloth pieces to fit as a double layer into the base of the bar dishes.  
D.2.3  General  — Balance to weigh 1 300 grams to 0.1 g if the bar and weighted holder shall be weighed together.  
If the weight can be easily separated from the holder, then it is only the holder (typically not m ore than 100 grams) 
plus bar which need be weighed and the balance can have a smaller capacity.  DRS 88: 202 1 
13                ©RSB 2021  - All rights reserved  
 D.3 Bar preparation  
D.3.1  A test piece is cut from each bar. The test piece shall have a working face (to be applied to the fabric) of 
3.75 cm x 7.5 cm.  
The working  face shall be a fresh surface from the interior of the bar sample.  
The 7.5 cm length of the test piece shall be from a direction parallel to the longest axis of the original bar  sample.  
The height of the test piece is whatever is needed to fit securely into the test piece holder and to leave sufficient 
product below the holder to allow for wear during the test.  Typically , the depth shall be 2 cm to 3.5 cm.  
D.3.2  To cut the bar, it is convenient to first trim it to the approximate size using a coarse kit chen cheese grater 
and then to make the final adjustments to a smooth surface with a sharp thin bladed knife.  
D.4 Test procedure  
D.4.1  Preconditioning the test bar  — In this stage it is not necessary to weigh the bar.  
D.4.1.1  A small tray (bar dish) plus doubl e thickness of cloth is filled with demineralized water.  The tray is then 
held vertically to drain the water from the cloth.  The vertical position is maintained until water ceases to run from 
the dish in a continuous stream, i.e. drained to dripping.  
D.4.1.2 The cut bar piece is placed on the wetted cloth for 1 hour at room temperature, approximately 25 ºC. This 
procedure allows the bar surface to absorb water (from mush) in a way characteristic of the product during use.  
The mushed test piece is fitted into a bar holder with the mushed face to the outside.  
D.4.1.3  The bar is dried lightly with tissue.  The bar is now preconditioned to a state typically met during normal 
use.  The main wear test can now be performed.  
D.4.2  The wear test  
D.4.2.1  A fresh pi ece of test fabric is immersed in normal supply water and is then held vertically by the corners of 
a shorter edge.  The cloth shall be held so that one of the corners is at the lowest point.  Water shall drain from the 
cloth, initially in a continuous str eam and eventually as drops.  As soon as the continuous stream ceases and drops 
are formed, the cloth is placed flat on the test tray and smoothed to remove wrinkles, creases or bubbles.  A shorter 
edge of the cloth shall be nearest the operator.  
C.4.2.2  The test bar and weighted holder, or the holder plus bar only, are weighed to the nearest  
0.1 g.  
C.4.2.3  The test face of the preconditioned bar in the holder is placed towards one edge of the fabric and is 
then moved away from the operator towards the other shorter edge.  
NOTE  The effective cloth length shall be the distance moved by the leading edge of the bar, not the length of the cloth.   
©RSB 20 21 - All rights reserved                  14 
 D.4.2.4  The holder/bar are repositioned at the edge closest to the operator in a new position adjacent to the 
previ ous position and such that it is on fabric which was not rubbed in the previous step.  
D.4.2.5  Steps D.4.2.3  and D.4.2.4  are repeated such that, in total the bar is moved four (4) times along the 
length of the fabric.  
D.4.2.6  The bar is dried lightly with t issue and the weighed holder plus bar, or holder plus bar only, are  re-
weighed to give the weight loss during the fabric application.  
D.4.2.7  Provided the sample size is adequate, the wear test can be repeated with two more measures of wear 
on the same sam ple. The complete wear test is then repeated with two more examples of the product giving 
nine (9) measures of wear. If the sample size is not adequate to allow replicate tests on a given sample then 
nine individual samples shall be used.  
D.4.2.8  The avera ge weight loss for movement over 4 times the effective cloth length is calculated for the nine 
samples of a given product, and then expressed as weight loss per metre of application to the fabric.  DRS 88: 202 1 
15                ©RSB 2021  - All rights reserved  
 Annex  E 
(normative)  
 
Determination of the potential mush  
E.1 Principle  
A test bar piece of defined size is cut from the sample bar to remove harder outer layers. The test piece is 
preconditioned by giving 18 x 180 degree twists under running water at 25 ºC or in a bowl of water.  The bar is 
left for six hours on a piece of f abric which has been wetted and drained of excess water.  During the six hours, 
the bar/cloth is covered to prevent drying.  At the end of the test period, mush is removed from the test piece 
face in contact with the cloth.  Weight loss from the test piece  is expressed as mush per 30 sq.cm of original 
surface area in contact with the cloth.  
E.2 Equipment  
E.2.1  For sample preparation  
bb) Coarse kitchen cheese grater;  
cc) Sharp thin blade knife;  
dd) Callipers or ruler to ensure the sample dimensions  
E.2.2  Other equipment/mat erials  
(a) Plastic or non corrodible trays which are suitably sized for the test piece;  
(b) Plastic bar dishes 7 cm x 11 cm x 2 cm shall be suitable.  
Cotton cloth pieces are cut to fit as a double layer inside the trays.  The cotton cloth used for wear measurements 
(Appendix B) shall be suitable.  
E.3 Bar preparation  
E.3.1  Nine (9) individual bars shall be tested. A test piece is cut from each bar. The test piece shall have a 
working face (to be applied to the fabric) of 4.0 cm x 7.5 cm.  
The working face shall be a fresh surface from the interior of the bar sample. The face opposite the working 
face shall be identified by making a small hole with a sharp object. This enables the working face to be identified 
after the preconditioning step.  
The 7.5 cm lengt h of the test piece is from a direction parallel to the longest axis of the original bar sample.   
©RSB 20 21 - All rights reserved                  16 
 E 3 2  To cut the bar, it is convenient to first trim it to the approximate size using a coarse kitchen cheese 
grater and then to make the final adjustments to a smooth surface with a sharp thin -bladed knife.  
E.4 Test procedure  
For each test piece:  
D.4.1 The tray plus double thickness of cloth is filled with de -mineralized water. The tray is then held vertically 
to drain the water from the cloth. The vertical positio n is maintained until water ceases to run from the dish in a 
continuous stream, i.e. starts to drip.  
D.4.2 The area of the working face of the test piece is measured.  
D.4.3  The bar is preconditioned by giving 18 twists of 180 degrees under running supply w ater at 25 ºC in a 
bowl of supply water at that temperature.  
D.4.4 The working face of the bar is placed onto the damp fabric and then the tray plus bar are covered, e.g. 
with a sealed plastic bag, to prevent water loss.  
D.4.5 The covered test piece and ho lder are maintained at 25 ºC for 6 hours.  
D.4.6 The mushed bar test piece is removed from the tray and is weighed.  
D.4.7 Mush is removed from the working face of the bar test piece by scraping with a blunt sided spatula or 
plastic ruler.  
D.4.8 The test pie ce is reweighed and the amount of mush removed is calculated.  The mush is expressed 
as grams per 30 sq. cm of original test piece surface area.  
NOTE  The procedure for weighing the bar and removing the mush shall take some minutes. During that time the 
remaining bars will continue to form mush. While this time is not critical for a set of nine (9) test pieces from a given produc t, 
if more than one product is under test, it is advisable to stagger the start of the test for the second product. This shall g ive 
adequate time to complete wor k on the first set before the 6 hour storage time of the subsequent set is completed.  DRS 88: 202 1 
17                ©RSB 2021  - All rights reserved  
 Annex  F 
(normative)  
 
Test for freedom from grit  
F.1 Outline of the method  
Soap is rubbed with water between the hands for a specified  time and examined  for its gritty or rough feel, if 
any. 
F.2 Procedure  
F.2.1  Hold the laundry bar under running tap water (at a temperature between 20 ºC – 30 ºC) and rub gently 
the two sides of the bar on the palm for one minute each. The bar shall show no rough surface and shall feel 
smooth to the touch. Allow the used bar to dry in the open for 4 hours and examine the surface.  
F.2.2  The soap shall be taken to have passed the test if there is no  gritty or rough feel on the surface.  
 
 DRS 88: 202 1 
 
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