ISO 21046:2018

Silk - Test method for determining the size of silk yarns

This document specifies the test method for determining the size of silk yarns in all types of package forms. It is applicable to various kinds of silk yarns. It is not applicable to spun silk yarns.

Soie — Méthode d'essai pour déterminer le titre des fils de soie

General Information

• Status: Published
• Publication Date: 30-Oct-2018
• ICS: 59.080.01 - Textiles in general
• Technical Committee: ISO/TC 38/SC 23 - Fibres and yarns
• Drafting Committee: ISO/TC 38/SC 23/WG 5 - Fibres - Natural proteins
• Current Stage: 9093 - International Standard confirmed
• Start Date: 26-Jun-2025
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO 12643-5:2023 - Graphic technology - Safety requirements for graphic technology equipment and systems - Part 5: Manually-fed stand-alone platen presses
• Effective Date: 06-Jun-2022

Overview

ISO 21046:2018 specifies a standardized test method for determining the size (linear density) of silk yarns in all package forms (skeins, cones, bobbins). Applicable to raw silk, tussah, dupion, thrown silk and similar natural-silk yarns, the standard is not applicable to spun silk yarns. It defines sampling, conditioning, apparatus, weighing, drying and calculation procedures so that results (expressed in dtex or denier) are comparable across laboratories and commercial transactions.

Key topics and technical requirements

• Definition of size: linear density (mass per unit length), expressed in dtex (or denier; 1 den = 0.9 dtex per ISO 1144).
• Sampling & sample length: sizing skein length is 112.5 m (e.g., 100 revolutions on a 1 125 mm wrap reel or 112.5 revolutions on a 1 000 mm reel).
• Sample quantity: a multiple of 50 skeins; default test amounts are 100 skeins for nominal size ≥78 dtex and 200 skeins for <78 dtex.
• Conditioning: atmospheres per ISO 139; condition samples for a minimum of 12 hours prior to testing and maintain condition during testing.
• Apparatus:
  • Wrap reel: circumference (1 125 ± 2.5) mm, speed (300 ± 15) r/min, or equivalent positive-feed at controlled tension (0.05 ± 0.01 cN/dtex).
  • Balance resolution ≤ 0.001 g; size tester resolution ≤ 0.25 dtex.
  • Oven: drying at (140 ± 2) °C (as specified).
• Weighing & rounding rules: weigh skeins individually and in 50-skein groups; rounding varies with size (e.g., <56 dtex to 0.5 dtex; 56–166 dtex to 1.0 dtex; ≥167 dtex to 2.0 dtex).
• Data control & tolerances: compare sum of individually measured sizes with the total-group size; specific tolerances depend on nominal size (table provided in the standard).
• Conditioned size & moisture: conditioned size accounts for commercial moisture regain (historically 11.0% for silk) by weighing to constant mass after oven drying (constant mass = successive weights differing by <0.1%).
• Calculations: compute average size, size deviation (standard deviation), maximum size deviation (top/bottom 2% assessment), and coefficient of variation (CV) with prescribed rounding.

Applications and users

ISO 21046:2018 is intended for:

• Textile testing laboratories performing quality control and certification of silk yarns.
• Silk producers and reeling houses requiring consistent sizing data for sales and specification compliance.
• Yarn traders and quality assurance teams verifying commercial mass/linear density for lot acceptance.
• R&D groups studying yarn uniformity, process control, and product development for silk applications.

Practical uses include lot acceptance testing, incoming inspection, process control in reeling/throwing, and supporting contractual specifications where accurate, reproducible dtex measurements are required.

Related standards

• ISO 2060 - size (linear density) test methods for many conventional yarns (not fully applicable to silk; ISO 21046 covers silk-specific requirements).
• ISO 139 - standard atmospheres for conditioning and testing.
• ISO 6741-1:1989 - mass determination and oven-drying procedures referenced for commercial mass calculations.

Keywords: ISO 21046:2018, silk yarn sizing, test method, dtex, conditioned size, wrap reel, size deviation, silk yarn testing.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21046
First edition
2018-11
Silk — Test method for determining
the size of silk yarns
Soie — Méthode d'essai pour déterminer le titre des fils de soie
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
6 Atmosphere for conditioning and testing . 3
7 Procedure. 3
7.1 Sampling . 3
7.1.1 Sample length . 3
7.1.2 Sample quantity . 3
7.2 Preparation . 3
7.3 Weighing . 3
7.4 Data control . 4
7.5 Conditioned size . 4
8 Calculations. 4
8.1 General . 4
8.2 Average size . 5
8.3 Size deviation . 5
8.4 Maximum size deviation . 5
8.5 Conditioned size . 5
8.6 CV .
size 6
9 Test report . 6
Annex A (informative) Determination of drying time . 7
Annex B (informative) Tolerance between conditioned size and average size .8
Annex C (informative) Example of size test results for silk yarn . 9
Bibliography .11
Foreword
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This document was prepared by Technical Committee ISO/TC 38, Textiles, Subcommittee SC 23, Fibres
and yarns.
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iv © ISO 2018 – All rights reserved

Introduction
Silk yarns are made of natural silk fibres, including raw silk, tussah silk, dupion silk, thrown silk, etc.
Due to the intrinsic unevenness of the property of silk fibres and its manufacturing technique differing
from yarns made of staple fibres, the size (linear density) deviation of the silk yarns, such as raw silk
reeled from cocoon baves, is much bigger than that of the conventional yarns covered by ISO 2060.
Therefore, when measuring the size of silk yarns, the sample quantity, sample length, test device,
drying temperature, test items, calculation method of the results and tolerance for weighing errors are
all different from that for the conventional yarns. These special requirements are not prescribed in
ISO 2060. This document covers special size test regulations for silk yarns which are not covered by
ISO 2060.
INTERNATIONAL STANDARD ISO 21046:2018(E)
Silk — Test method for determining the size of silk yarns
1 Scope
This document specifies the test method for determining the size of silk yarns in all types of
package forms.
It is applicable to various kinds of silk yarns.
It is not applicable to spun silk yarns.
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 139, Textiles — Standard atmospheres for conditioning and testing
ISO 6741-1:1989, Textiles — Fibres and yarns — Determination of commercial mass of consignments —
Part 1: Mass determination and calculations
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
silk yarn
yarn made of nature silk fibres, including raw silk, tussah silk, dupion silk, thrown silk
3.2
thrown silk
silk that has been twisted or doubled and twisted
3.3
size
linear density (mass per unit length) of silk yarns
Note 1 to entry: Size expresses the degree of coarseness or fineness of silk yarns.
Note 2 to entry: Size is expressed in dtex. It may also be expressed in deniers (den), for which the conversion from
[1]
dtex, as given in ISO 1144 , is 1 den = 0,9 dtex.
3.4
nominal size
size indicated by the manufacturer
3.5
average size
average value of the tested size of the sizing skeins
3.6
conditioned size
size calculated by adding the commercial moisture regain weight to the oven-dry weight
Note 1 to entry: For silk, the commercial moisture regain is 11,0 %, which was developed in 1841, and then was
widely used by Japan, China, India, etc. See Reference [4].
3.7
size deviation
standard deviation of the value of the tested size of the silk samples indicating the deviation degree of
the sizing skeins from the average size of the whole lot
3.8
maximum size deviation
indication of the deviation degree of the finest sizing skeins or the coarsest sizing skeins from the
average size of the whole lot
3.9
coefficient of variation of size
CV
size
percentage ratio between the size deviation and the average size
4 Principle
Under standard atmosphere, the sizing skeins are prepared by winding prescribed revolutions of silk
yarn on a reel with a
...