ISO/TR 18942:2020

TECHNICAL ISO/TR
REPORT 18942
First edition
2020-04
Imaging materials — Evaluation of
image permanence of photographic
colour prints in consumer home
applications
Support d'image — Évaluation de la permanence de l'image de
tirages couleur photographiques dans les applications domestiques
grand public
Reference number
ISO/TR 18942:2020(E)
©
ISO 2020

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ISO/TR 18942:2020(E)

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ISO/TR 18942:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview . 1
4.1 General . 1
4.2 Use case . 2
4.3 Single factor tests and their limitations . 3
4.4 Accelerated tests and the concept of reciprocity . 3
4.5 Concepts and limitations of data reporting. 4
5 Preparation of test targets and analysis . 5
5.1 General . 5
5.2 Factors influencing the test results . 5
5.2.1 Test design . 5
5.2.2 Test conditions. 5
5.2.3 Measurements . 6
5.3 Test target . 6
5.3.1 General. 6
5.3.2 Humidity test target (ISO 18946) .10
5.4 Measurement (Density and colorimetric values) .11
5.4.1 General.11
5.4.2 Density values to be measured .11
5.4.3 Colorimetric values to be measured .12
5.4.4 Discussion of densitometric and colorimetric approaches . .13
5.5 Preconditioning .14
6 Test methods .14
6.1 General .14
6.2 Thermal stability .14
6.3 Light stability (Indoor display) .16
6.4 Ozone gas stability .19
6.5 Humidity fastness .24
7 End of test criteria .27
7.1 General .27
7.2 Initial optical density and colour .27
7.3 List of several sets of end of test criteria for background explanation.28
8 Environmental conditions .28
8.1 General .28
8.2 Temperature and humidity .29
8.3 Light .31
8.4 Ozone .34
8.5 Conclusion .37
8.6 General .37
8.7 Basic reporting .37
8.7.1 Graph reporting .37
8.7.2 Fixed-load reporting .39
8.7.3 Discussion of graph reporting and fixed-load reporting .41
8.8 Advanced reporting .43
8.8.1 Two advanced reporting methods .43
8.8.2 Reporting "year rating" .43
8.8.3 Reporting “Star rating” .44
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ISO/TR 18942:2020(E)

8.8.4 Discussion for usage of Star rating reporting .46
8.9 Others .46
Annex A (informative) Accidental test .48
Annex B (informative) Other reporting .51
Bibliography .54
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ISO/TR 18942:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 42, Photography.
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.
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ISO/TR 18942:2020(E)

Introduction
Reflection colour photographic-indoor stability specifications for consumer home have been discussed
(Physical properties and image permanence of photographic materials). Many matters have been
discussed about environmental data, psychophysically based end of test, nominal use case conditions,
and mechanics of rating system, reciprocity issues, and experimental testing issues in the meetings.
This document describes cumulated information, data and knowledge work over the last 15 years as
‘Guidelines for print-life-estimations’. Furthermore, it describes the background and the history of the
discussion in TC 42/WG 5.
The purpose of this document provides data, information, and indicating the guidelines for evaluation
of image permanence. These data and information were introduced and discussed and were quoted
from the papers reported in conferences by TC 42/WG 5 members. Furthermore, detailed information
and understanding are available in the references listed in the Bibliography in this paper.
It describes four important environmental stressors (heat, light, atmospheric pollutants, and humidity)
in main body of this document. Ozone was chosen as the model system for atmospheric pollutant,
but SO , NO and other atmospheric pollutants are present in the indoor environment. In addition, it
x x
includes an Annex A about accidental stressor (water, abrasion and others), examples of many topics
and useful data collections and information.
Information about the stability of colour photographs toward these various factors can be obtained
by accelerated stability tests. The starting assumption for indoor use cases is that the various
environmental factors (heat, light, atmospheric pollutants, and humidity) each act independently on
the photograph, i.e., there are no synergistic interactions taking place between these factors under
typical storage and display conditions. While interactions most certainly do take place in the real
world, modelling and testing for interactions is extremely difficult. The accelerated tests are therefore
designed such that only one factor (heat, light, atmospheric pollutants and humidity) is varied at a time.
The other factors not under investigation are controlled or held at a level that will induce only negligible
changes in the image during the course of the accelerated test.
In accelerated testing, high levels or “loads” are required for each of the factors in test in order to
complete the tests in a reasonable amount of time. The validity of accelerated testing for light and
pollutants assumes that equal change will occur for the same cumulative exposure, i.e., one assumes
reciprocity for the dose. However, for some systems “reciprocity failure” has been observed. When
applied to light-induced fading and staining of colour images, reciprocity failure refers to the failure
of many colorants to fade, or to form stain, equally when irradiated with high-intensity versus low-
intensity light, even though the total light exposure (intensity × time) is kept constant through
appropriate adjustments in exposure duration. This concept can be applied to any accelerated test
where the same cumulative exposure can be obtained by different intensities or concentrations and
time. Note, however, that this concept cannot be applied to accelerate testing for heat or humidity
where special test procedures are required. This concept does hold for ozone stability testing, where
the ozone concentration can be high or low. The extent of colorant fading, colorant migration, and stain
formation can be greater or smaller under accelerated conditions, depending on the chemical reactions
involved in the colorant degradation, on the kind of colorant dispersion, on the nature of the binder
material, and on other variables. For example, the supply of oxygen that can diffuse into a photograph’s
image-containing layers from the surrounding atmosphere may be restricted in an accelerated test
(dry gelatine, for example, is an oxygen barrier). This may change the rate of colorant fading relative
to the fading that would occur under normal display conditions. The magnitude of reciprocity failure
may also be influenced by the temperature and moisture content of the test specimen. Comparisons
between products will more accurately reflect observed differences when accelerated aging conditions
are close to actual use conditions.
The following International Standards describe test methods relating to indoor stability. These
Standards provide procedures for reporting technical data.
A test method for thermal stability is described in ISO 18936. A test method for humidity fastness is
described in ISO 18946. A test method for indoor light stability is described in ISO 18937. A test method
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for ozone gas fading stability is described in ISO 18941. A test method for stability under low humidity
conditions in ISO 18949.
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TECHNICAL REPORT ISO/TR 18942:2020(E)
Imaging materials — Evaluation of image permanence of
photographic colour prints in consumer home applications
1 Scope
This document provides data and information related to evaluation of image permanence of
photographic colour prints in consumer home applications. This document characterizes the test
methods, the end of test criteria, the environmental factors, and the reporting. It also provides the
background and the history of those.
This document describes guidelines and limitations for print life estimates, i.e. translation of the test
results to the performance in actual usage as well as limitations of such a translation.
The photographic colour prints printed digitally described in this document can be generated with dyes
or pigments by several processes, including ink jet, chromogenic (silver halide), thermal dye transfer
processes, and electro photography, excluding lithographic printing, screen printing and other non-
digital printing.
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 18913, Imaging materials — Permanence — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18913 and the following 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
test load
cumulative dose, which is the product of a stress level and exposure time
3.2
specimen aim temperature
controlled aim value temperature of the specimen by configuring the light exposure equipment
4 Overview
4.1 General
This document describes approaches for the evaluation of image permanence of photographic colour
prints in consumer home applications. The use profile “consumer home” is defined with two sub-cases i)
display and ii) storage. In addition, variants of the use profile due to “partial protection” are introduced.
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Then, suitable accelerated test methods representing single factor testing of the four leading
environmental factors are described, which are considered important for characterization of image
permanence in this use profile. Limitations of these laboratory tests are set into perspective.
Different approaches of collecting and reporting test data are presented. In addition, the advanced
reporting level based on eventual translation of test data into print life expectations is introduced
together with limitations of such predictions.
The definition of end of test and the interdependence of their meaning with test target design and
evaluation metrics are discussed.
4.2 Use case
Within the consumer home use profile, there are two main use cases for colour photographic images,
namely display and dark storage, in which the four leading environmental stress factors heat, light,
atmospheric pollutants and humidity have different weights. In both, additional (partial) protection
against some environmental factors may be introduced by suitable enclosures that create a “micro-
environment”, in which the level of one or several environmental factors is reduced. For example,
framing of displayed colour prints with glass, plastic, or other materials can introduce additional
protection against degradation caused by light or pollutants or both. In dark storage, light-tight
enclosures, such as “shoe box” and albums, first of all will help to reduce the level of light exposure as
well as help to reduce the level of active atmospheric pollutants due to the lack of air exchange inside
the box. Levels of heat and humidity could only be reduced by air-conditioned environments as shown
in Table 1.
Table 1 — Major and minor stressors for various storage and display use cases
Heat Light Atmospheric Humidity
Pollutants
Dark Storage Major Not a factor Minor Major
Protected
Dark Storage Major Not a factor Major Major
Unprotected
Display Major Major Not a factor Minor
Protected
Display Major Major Major Major
Unprotected
NOTE 1 Additional protection in storage and display environments can be provided as follows:
a) In the dark environment by enclosures which limit air exchange;
b) In the light environment by framing with UV absorbing glass which reduces damaging light and
also limits air exchange.
NOTE 2 The “Display Protected” category is considered to be “Not a Factor” for atmospheric pollutants only
if the protecting frame is sealed to prevent any exchange of air. Atmospheric pollutants, such as ozone, are
extremely reactive and are not retained in closed (protected) spaces, while humidity can penetrate into the
enclosure and remains for a long period.
NOTE 3 Dark storage protected and display protected provides protection against short-term humidity
excursions.
Typical ranges of environmental factors in the use profiles “consumer home” are given in Clause 8.
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4.3 Single factor tests and their limitations
A typical approach for image permanence testing for indoor use profiles is based on single factor
accelerated test methods that assess the susceptibility of the print to degrade for each of the four
leading environmental factors one at a time. Prints are exposed to one of the factors heat, light, humidity
and atmospheric pollutants and the other stress factors are set to zero or a ‘neutral’ level. Ozone was
chosen as model system for atmospheric pollutant, acknowledging that SO , NO and other atmospheric
x x
pollutants are also present in the indoor environment and that exposure to these may result in different
[1][2]
image fading results . A considerable level of acceleration is needed in the test methods for the
evaluation of degradation by heat, light, ozone, and humidity, because the degradation of many modern
colour print images by these stress factors is too slow to yield timely information about their long-term
effects.
For example, in assessing the image degradation of a reflection print due to exposure to light, the
accelerated test method in ISO 18937 specifies that the test be conducted under air that contains
<2 nl/l ozone at an air temperature and relative humidity of 21 °C to 27 °C for control specimen aim
temperature and 50 % ± 5 % RH, respectively. These conditions ensure that any image degradation
observed will be due primarily to light exposure and not to ozone, thermal, or humidity. These are
designed to minimize the contribution from each other.
An overview of the single factor test methods and their setting for the other environmental factors is
described in Table 2. Users can set conditions by controlling their testing equipment.
Table 2 — Test conditions described in test methods International Standards
Reference ISO Heat Light Ozone Humidity
Thermal stability ISO 18936 main factor dark <2 nl/l 50 % RH
Light stability ISO 18937 21 °C–27 °C main factor <2 nl/l 50 % RH
Ozone stability ISO 19841 23 °C dark main factor 50 % RH
Humidity resistance ISO 18946 25 °C dark <2 nl/l main factor
The conditions in the top row (Thermal stability) are not a strictly pure single-factor test of heat; it
actually includes the combined stress contributions from both humidity content and temperature. The
variation ranges of moisture content of the humidity test conditions listed in the bottom row (Humidity
resistance) is a sub-set (within the variation range) of moisture content in the thermal test, but without
the involvement of temperature variation.
Some caveats need to be considered, when prints are tested together with some means of protection.
For example, testing light stability of framed specimen print with glazing may result in elevated
specimen temperature. In addition, material that may outgas during the test could become trapped in
the vicinity of the test specimen, and induce additional image degradation. Similarly, test specimens
that are laminated may also be subject to interactions that may confound the test results. The user is
cautioned to keep such phenomena in mind if unexpected results occur.
This document advises the use of standard test parameter settings with fixed exposure or test load
conditions to collect test data for reporting. It is recognized that other test parameter settings may be more
representative for particular instances of the use profile or other applications. These other conditions
may then be reported in addition and to the standard test parameters settings mentioned before.
The user of this document is advised that the actual image degradation that is observed by the end user
or consumer will be a combination of all the degradation modes discussed above. However, complex
interactions may exist between these different failure modes, which are not covered by the single
stress factor of test approach. For example, the reported photochemical instability of the yellow stain
[15]
developed during thermal aging makes simple linear combinations inappropriate.
4.4 Accelerated tests and the concept of reciprocity
An important element of accelerated testing is the level of reliability obtained for the predicted results.
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In thermal testing, for example, the underlying model for acceleration is based on a first order thermally
activated process. The validity of that assumption is verified by a linear dependence of data in the well-
known” Arrhenius-plot” described in ISO 18924.
The accelerated testing of degradation under both, light and ozone, is based on the concept of
reciprocity. In the case of light, the principle of reciprocity states that increasing the incident light
intensity without changing the spectral distribution of the illumination, while maintaining the same
temper
...