ISO 21575:2026

International
Standard
ISO 21575
Second edition
Raw optical glass — Powder test
2026-01
method for the water resistance of
optical glass — Test method and
classification
Verre optique brut — Méthode d'essai sur poudre pour
déterminer la résistance à l'eau du verre optique — Méthode
d'essai et classification
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 1
5 Reagents . 1
6 Apparatus . 2
7 Preparation of the specimen of the glass to be tested . 3
8 Procedure . 4
9 Classification and designation . 4
10 Test report . 5

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 3,
Optical materials and components.
This second edition cancels and replaces the first edition (ISO 21575:2018), which has been technically
revised.
The main changes are as follows:
— change of title;
— the term “weight” has been changed to “mass” in the entire document;
— 5.1 and 6.1 have been added;
— Figure 3 has been added;
— the information required for the test report has been revised;
— editorial changes;
— the term “specific gravity” has been changed to “mass density” in Clause 7 b) and Clause 8 a) and the
formula for calculating mass density from specific gravity has been added as a note in Clause 7 b).
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.

iv
Introduction
There are two commonly used methods for testing the chemical resistance of optical glass: The powder
method and the surface method. The powder method has simpler procedures for the sample preparation
since it does not require a homoge
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