ISO 18929:2012

INTERNATIONAL ISO
STANDARD 18929
Second edition
2012-04-01
Imaging materials — Wet-processed
silver-gelatin type black-and-white
photographic reflection prints —
Specifications for dark storage
Matériaux pour l’image — Tirages photographiques par réflexion
par traitement humide gélatinoargentique de type noir et blanc —
Spécifications pour le stockage dans l’obscurité
Reference number
©
ISO 2012
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ii © ISO 2012 – All rights reserved

Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Safety and operational precautions . 2
4.1 Hazard warnings . 2
4.2 Hazard information code system . 2
4.3 Safety precautions . 3
5 Requirements for physical stability of prints . 3
5.1 Wedge brittleness . 3
5.2 Tensile energy absorption (see Annex C) . 3
5.3 Resin cracking of RC papers (see Annex D) . 3
6 Requirements for processed image stability (see Annex E) . 3
6.1 Residual thiosulfate concentration . 3
6.2 Residual silver concentration . 4
6.3 Yellowing limit (see Annex G) . 4
7 LE designation . 4
8 Test methods . 4
8.1 Wedge brittleness . 4
8.2 Tensile energy absorption . 5
8.3 Yellowing . 6
8.4 Residual silver compound test using cyanogen iodide (CNI) extraction . 6
8.5 Residual silver compound test by use of sulfuric acid/nitric acid extraction . 7
8.6 Resin cracking . 8
Annex A (informative) Stabilization treatments to prevent silver oxidation . 11
Annex B (informative) Potential silver-image discolouration of RC prints under display conditions .12
Annex C (informative) Tensile energy absorption .13
Annex D (informative) Environmental resin-cracking .14
Annex E (informative) Effects of residual thiosulfate and silver in processed prints .15
Annex F (informative) Degradation of silver images due to extraneous oxidation .17
Annex G (informative) Discolouration of black-and-white photographic prints .18
Annex H (informative) Densitometric versus spectrophotometric measurement of yellowing .20
Bibliography .21
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 18929 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 18929:2003), which has been technically revised.
iv © ISO 2012 – All rights reserved

Introduction
Black-and-white silver-gelatin fibre-base papers have been important imaging materials for well over 100 years.
Reflection prints, made with such papers, have become increasingly important pictorial and documentary
records that are housed in many libraries, archives, museums, universities and other public and private
institutions. Although the intrinsic stability of properly processed and stored silver-gelatin prints is very good,
there are internal and external factors that can cause degradation of such prints during storage and shorten
their useful life. This International Standard provides specifications for tests that evaluate the stability of black-
and-white silver-gelatin prints under prescribed storage conditions. It does not cover tests for the possible
harmful effects of extended exposure to light.
Black-and-white prints are laminates, whose main components are a paper base, a white opaque intermediate
layer, an image layer, and a protective layer. Paper has been used as a support for prints since about 1840. The
history of its evolution into a very stable, high alpha-cellulose type fibre-base in the 1920s and to a polyethylene
resin-coated (RC) paper base in the 1960s has been covered extensively in the literature (see References [11],
[12], [13], [14] and [15]).
The intermediate, white opaque layer can be of two types. For fibre paper, since the 1880s it has been a gelatin
layer containing white barium sulfate pigment (baryta layer) and other additives that enhance the paper’s
reflectivity, hardness, holdout, adhesion and surface characteristics (glossy, matte, textured). The second
type came into use in the 1960s with the introduction of an RC base. This has a paper core coated on both
sides with water-impermeable extruded polyethylene layers. The top layer contains white titanium dioxide
pigment that provides higher reflectivity than barium sulfate; the bottom layer is transparent and formulated to
counteract the curl induced by the emulsion, which is coated on top of the pigmented layer.
Prints on fibre paper have the advantage of having demonstrated long-term stability from years of practical
experience in both dark storage and in reasonable display conditions. Proper processing and cleanliness or
lack of contamination are important. Diluted toning solutions have been used successfully to enhance stability
(see Annex A).
Prints on an RC paper base offer the advantages of higher wet strength, reduction in washing and drying times,
lower consumption of processing chemicals, better dimensional stability, lower curl, and freedom from cockle and
other effects of differential shrinkage. As with fibre-base materials, toning has been used successfully to enhance
stability. However, they can suffer from stability-related problems such as light-induced image discolouration,
silver mirroring, yellowing and cracking of the polyethylene layer (see References [16], [17], [18] and [19]).
This International Standard only applies to prints in dark storage since an applicable test for light-induced image
deterioration has not been agreed upon. One reason for this has been that different brands of RC papers, or
papers manufactured at different periods, have exhibited widely varying stability characteristics. It has been
very difficult to reconcile all of the observed differences in behaviour in a relatively simple standardized test
(see Annex B).
The image layer of most black-and-white prints is a gelatin coating containing a dispersion of light-sensitive
silver halide crystals that are selectively converted into metallic silver grains by an image-forming exposure and
chemical processing. Gelatin is a natural polymer that has been the preferred binder for photographic materials
since the 1880s because it has proven to be the best protective colloid for the precipitation, growth and
controlled suspension of silver crystals and for the formation of a dry, flexible image layer during a subsequent
coating operation. Gelatin also can be hardened to reduce its swelling and susceptibility to physical damage,
without blocking the absorption and desorption of aqueous processing solutions required for image formation
and removal or stabilization of chemical by-products (see References [20] and [21]).
Converting the metallic silver to a complex or pre-oxidized form of silver will improve image stability. Many toner
solutions have been designed to accomplish this, such as selenium, sepia, gold, brown and poly-toners. For
example, in the case of sepia toner treatment, the silver is converted from oxidizable metallic silver to a stable
silver sulfide.
The storage stability and useful life of reflection black-and-white prints depends on their physical and chemical
properties, as well as on the conditions under which they are stored. For many years, the term “archival
medium” was used to designate a recording material that can be expected to retain information forever so that
it can be retrieved without significant loss when properly stored. However, there is no such material and it is a
term no longer employed for material or systems specifications of International Standards. Another reason for
abandonment of the term is the multiplicity of meanings that it acquired over the years, ranging from “preserving
information forever” to “temporary storage of actively used information”. The unambiguous term used in this
International Standard is “life expectancy” (LE), defined as the length of time that information is predicted to be
retrievable in a system after storage. For example, a designation of LE-100 indicates that the information can
be retrieved without significant loss after at least 100 years. Reflection prints are classified according to their
LE designation in this International Standard.
vi © ISO 2012 – All rights reserved

INTERNATIONAL STANDARD ISO 18929:2012(E)
Imaging materials — Wet-processed silver-gelatin type black-
and-white photographic reflection prints — Specifications for
dark storage
1 Scope
This International Standard establishes the specifications for silver-gelatin photographic reflection prints
intended for dark storage. It covers silver-gelatin print types of all weights.
This International Standard applies to wet-processed black-and-white silver-gelatin photographic prints,
including those that have been chemically treated (with a gold, selenium, sulfur, or other chemical treatment
bath) to improve the permanence of the silver image. It also applies to silver-gelatin prints processed by a
monobath, which includes thiosulfate as a fixing agent followed by a conventional wash.
This International Standard is not applicable to instant black-and-white photographic prints, stabilization-
processed black-and-white prints (those where the
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