ISO 18935:2025

International
Standard
ISO 18935
Fourth edition
Imaging materials — Colour
2025-02
images — Determination of water
resistance of printed colour images
Matériaux pour l'image — Images en couleurs sur impressions
en papier — Détermination de la résistance interne de la couleur
à l'eau
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Categories of water resistance . 1
4.1 General .1
4.2 Water resistant . .1
4.3 Moderately water resistant .1
4.4 Not water resistant .2
5 Water resistance estimating procedures . 2
5.1 General considerations.2
5.2 Control sample .2
6 Test methods . 2
6.1 General .2
6.2 Method 1 — Standing water evaporation .3
6.3 Method 2 — Standing water plus wiping effects .3
6.4 Method 3 — Water soak .3
6.5 Method 4 — Edge immersion .3
7 Test pattern preparation . 4
7.1 General considerations.4
7.2 Example test patterns .4
8 Test report . 5
Annex A (informative) Determination of resistance to other liquids . 6
Annex B (informative) Water emergency scenarios with inkjet prints . 7
Bibliography . 8

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 42, Photography.
This fourth edition cancels and replaces the third edition (ISO 18935:2018), of which it constitutes a minor
revision.
The main changes are as follows:
— new informative annex on “Water emergency scenarios with inkjet prints”.
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
Water resistance is not an important consideration in the normal storage of colour prints. However, in a
disaster situation, such as floods, earthquakes or water main breaks, this property can be of critical
importance if the print is to be salvaged. A wide variety of materials are used for digital colour prints and
the colorants used in some digital prints are water soluble. The degree of their water resistance varies
depending upon the colorants used and if the print has a water-resistant overcoat. In addition, the paper
or other substrate may be of equal importance. The same colorants may exhibit very good water resistance
on one substrate but can be completely washed off from a different substrate. Even print systems that use
water-insoluble colorants may be damaged by water exposure if the substrate is not also water resistant.
This document provides a standardized method to evaluate the qualitative water resistance of colour prints.

v
International Standard ISO 18935:2025(en)
Imaging materials — Colour images — Determination of
water resistance of printed colour images
1 Scope
This document specifies tests to determine the relative water resistance of printed colour images. This
document is applicable to both digital and analogue prints.
2 Normative references
There are no normative references in this document.
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
ambient conditions
environmental conditions of (23 ± 1) °C and (50 ± 5) % RH
3.2
mordant
substance that combines with a dye, used to fix it in a material
4 Categories of water resistance
4.1 General
The water resistance of a print is categorized into one of three categories, i.e. water resistant, moderately
water resistant and not water resistant as defined in 4.2 to 4.4.
4.2 Water resistant
Water-resistant print is print that is not noticeably affected by exposure to liquid water.
NOTE No significant degradation of the colorant (bleeding, smearing, hue change), of the support (curl, cockle,
delamination) or of the image surface (gloss changes, water rings, etc.) is found.
4.3 Moderately water resistant
A moderately water-resistant print is a print that exhibits some change or damage by water but is still
considered usable for its intended application.
NOTE The damage can manifest itself as slight media curl, partial delamination along an edge, or ring-like
watermarks due to gloss changes or a minor amount of colorant migration. This damage can be mitigated by the rapid
removal of the water (careful blotting, shaking off the water, etc.).

4.4 Not water resistant
A print that is not water-resistant is a print that is easily damaged by contact with water, even when
incidental (e.g. a water mist) and is considered unsuitable for applications involving contact with water.
NOTE Such damage can manifest itself as appreciable curl, delamination of the image layer, colorant bleed into
non-imaged areas or from colour to colour, or image degradation (hue and gloss changes, surface marks, etc.). It is
strongly advisable to users of these materials to prevent water contact.
5 Water resistance estimating procedures
5.1 General considerations
Water resistance is the ability of a print to resist water damage which may manifest itself in a number of ways,
such as migration of colorants; changes in the size and/or optical density of image elements; degradation
of the image layer, as well as cockle, curl or loss of gloss. The water resistance of prints made by current
methods varies considerably. For example, some ink-jet prints sustain no observable damage when the
surface is rubbed immediately after water has been poured over the image. While others that do not show
any water damage after soaking for hours, lose a portion of their image layer if it is wiped off before drying.
For dye-based inkjet, water resistance of many systems is dependent on three interdependent variables:
[1]
ink absorption, coating solubility, and effectiveness of mordant . For other systems where the ink is not
absorbed into the substrate, water resistance is dependent on adhesion of the colorant to the substrate. In
both cases, water-resistant laminates will improve water resistance.
Extensive tests have shown that full characterization of water resistance requires several different
methods. Many attempts were made to quantify the test data generated by these methods in interlaboratory
comparison, but none were successful. It is likely that within a given laboratory, the tests described in this
document are sufficiently reproducible to yield statistically reliable data. However, this is not enough to
adopt fixed evaluation criteria. For these reasons, qualitative analysis of the test results is prescribed. This
entails grouping of the results obtained from different print materials into water-resistant (no change)
or not water-resistant categories. An intermediate level of moderate water resistance is also recognized,
...