ISO 18920:2011

INTERNATIONAL ISO
STANDARD 18920
Second edition
2011-10-01
Imaging materials — Reflection prints —
Storage practices
Matériaux pour l’image — Tirages par réflexion — Directives pour
l’archivage
Reference number
©
ISO 2011
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
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Published in Switzerland
ii © ISO 2011 – All rights reserved

Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Enclosures and containers . 3
5 Storage housings . 3
6 Storage rooms . 4
6.1 Medium-term storage rooms . 4
6.2 Extended-term storage rooms . 4
7 Environmental conditions . 4
7.1 Temperature and humidity specifications for storage . 4
7.2 Environmental conditioning requirements . 7
7.3 Air purity . 8
7.4 Light, use, and display . 8
8 Fire-protective storage . 9
9 Print identification, handling and inspection . 9
9.1 Identification . 9
9.2 Handling . 9
9.3 Inspection . 9
Annex A (informative) Humidity during storage . 11
Annex B (informative) Temperature during storage .12
Annex C (informative) Temperature/relative humidity relationship .13
Annex D (informative) Distinction between originals and copies made for active use .14
Annex E (informative) Air-entrained and gaseous impurities .16
Annex F (informative) Fire protection .17
Annex G (informative) Silver and colour image degradation.18
Annex H (informative) Cold storage practices .19
Annex I (informative) Print stability .20
Bibliography .22
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 18920 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 18920:2000), which has been technically revised.
iv © ISO 2011 – All rights reserved

Introduction
This International Standard is one of a series of standards dealing with the physical properties and stability of
imaging materials.
Photographic and other reflection prints, including hard-copy output from digital imaging systems, have
become increasingly important as documentary and pictorial reference material and art for consumers, as well
as in archives, libraries, government, commerce, museums and academia. This has focused attention on the
importance of preserving such materials to ensure their longest possible life.
The stability and useful life of reflection prints (hereafter referred to as prints) depend on their physical and
chemical properties, as well as on the conditions under which they are stored and used. This International
Standard provides recommendations on proper storage conditions and practices.
The important elements affecting the useful life of prints during storage are as follows:
a) relative humidity and temperature of the storage environment;
b) hazards of fire, water and light exposure;
c) fungal growth and other micro-organisms;
d) contact with certain chemicals in solid, liquid or gaseous form;
e) physical damage;
f) proper processing;
g) enclosures and containers in contact with the print material.
The extent to which the relative humidity and temperature of the storage environment, or variations of both,
can be permitted to reach beyond recommended limits without producing adverse effects will depend upon the
duration of exposure, biological conditions conducive to fungal growth and the accessibility of the atmosphere
to the print surfaces.
The term “archival” is no longer used to express longevity or stability in International Standards on imaging
materials since it has been interpreted to have many meanings, ranging from preserving documents “forever”,
which is unattainable, to temporary storage of actively used materials.
This International Standard defines two levels of recommended storage conditions: medium term and extended
term. Medium-term storage conditions can be used to preserve information for a minimum of 10 years. Extended-
term storage conditions can be used when it is desired to preserve information for as long as possible; these
conditions will prolong the life of all prints, even those not optimized for permanence.
The space requirements and costs for establishing and operating the two levels of storage conditions (medium
term and extended term) differ significantly. Furthermore, the ability to maintain specified limits of temperature
and relative humidity for both sets of storage conditions can be limited due to budgetary constraints, energy
considerations, climatic conditions, building construction, etc. However, any deviation from the specified
conditions will reduce the effectiveness of the storage environment. If such deviation is unavoidable, it is
advisable to select the lowest possible storage temperature that can be maintained. In any event, the best
preservation of prints will be attained with extended-term storage conditions.
This International Standard does not address the various strategies to upgrade substandard environments.
However, institutions with substandard environments and restricted budgets can plan for the improvement
of these environments as resources allow by judicious use of air conditioning, dehumidifiers (or humidifiers),
air circulation and filtration. Although practicalities might force compromises, any improvement in poor
conditions will add to the longevity of materials, even if they do not attain the life expectancies possible with
the environments recommended in this International Standard. The subject of basic air conditioning principles,
the various options and associated costs are outside the scope of this International Standard. There are many
references on this subject.
The storage of traditional paper collections is not within the scope of this International Standard. However,
many archives containing mixed recording media also include such collections. Archivists are encouraged to
review the appropriate standards for those materials specified in ISO 11799 and in the International Standards
listed in Clause 2.
The recommendations of this International Standard for the storage of prints encompass the following:
— storage enclosures, housing and rooms;
— atmospheric and environmental conditions;
— fire protection;
— handling and inspection procedures.
With the exception of fire and associated hazards that are sufficiently common to warrant inclusion of protective
measures, this International Standard does not pertain to means or methods for protecting photographic
reflection prints against natural or man-made catastrophes.
It is understood that the archivist of a multiple media collection might be forced to limit the number of storage
environments that can be provided. This compromise might be based on the value, physical size, quantity or
legal requirements to maximize life expectancy of some collections relative to others. The issues of mixed
media archives and recommendations for their storage are addressed in ISO 18934.
vi © ISO 2011 – All rights reserved

INTERNATIONAL STANDARD ISO 18920:2011(E)
Imaging materials — Reflection prints — Storage practices
1 Scope
This International Standard specifies dark storage conditions, storage facilities and procedures for the handling
and inspection of reflection prints of all types and sizes.
This International Standard is applicable to prints on the following opaque supports:
a) fibre-base paper;
b) RC (resin coated) paper;
c) pigmented and other types of plastic supports, e.g. polyester, cellulose acetate;
d) fabric, e.g. canvas, linen.
This International Standard is applicable to the following processed black-and-white silver gelatine prints:
1) wet-processed, including those that have been chemically treated to improve the permanence of the
silver image and/or to modify its colour, e.g. with gold, selenium or sulphur formulations;
1)
2) diffusion transfer, e.g. Polaroid and Fuji Photo Film instant prints ;
3) stabilization-processed (which contain the silver image as well as invisible, chemically stabilized
silver halides).
This International Standard is applicable to the following processed multicolour and monochrome colour
photographic prints:
i) chromogenic, washed and stabilized;
ii) silver dye bleach;
iii) dye transfer;
1)
iv) diffusion transfer, e.g. Polaroid and Fuji Photo Film instant prints , peel-apart or integral;
v) pigmented gelatine, e.g. carbon, carbro.
This International Standard is applicable to black-and-white and colour prints made with the following systems:
— thermal dye transfer (commonly referred to as dye sublimation);
— thermal wax transfer;
— electro-photographic;
— dye and pigmented ink jet;
— swellable and porous-coated media supports;
— diazo.
1) Polaroid and Fuji Photo Film instant prints are examples of suitable products available commercially. This information
is given for the convenience of users of this International Standard and does not constitute an endorsement by ISO of these
products.
Recommendations for storage of photographic films and storage of processed photographic plates are given
in ISO 18911 and ISO 18918 respectively.
This International Standard is applicable to medium-term and extended-term storage conditions, as
defined in Clause 3.
2 Normative references
The following referenced documents are indispensable for the application 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 18902, Imaging materials — Processed imaging materials — Albums, framing and storage materials
ISO 18916, Imaging materials — Processed imaging materials — Photographic activity test for enclosure materials
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
extended-term storage conditions
storage conditions suitable for the preservation of recorded information which has permanent value
3.2
fire-protective storage
facility designed to protect records against excessive temperatures, water and other fire-fighting agents, and
against steam developed by insulation of safes or caused by the extinguishing of fires and collapsing structures
3.3
fire-resistant vaults
fire-resistant vaults as defined in appropriate national standards and regulations
NOTE See References [9] and [17].
3.4
insulated record containers (Class 150)
insulated record containers (Class 150) as defined in appropriate national standards and regulations
NOTE See References [7] and [12].
3.5
life expectancy
LE
length of time that information is predicted to remain in an acceptable state when placed in a system at
21 °C and 50 % RH
NOTE In the past, the term “archival” was used to define material that could be expected to preserve images forever,
so that such images could be retrieved without significant loss when properly stored. However, as no such material
exists, this is now a deprecated term and is no longer used in International Standards for imaging materials or in systems
specifications.
3.6
medium-term storage conditions
storage conditions suitable for the preservation of recorded information for a minimum of 10 years
3.7
storage container
box or can be used to store prints
2 © ISO 2011 – All rights reserved

3.8
storage enclosure
any item in close or direct contact with recording material, such as folders, envelopes, sleeves, albums and mats
3.9
storage housing
physical structure supporting materials and their enclosures
NOTE This can consist of drawers, racks, shelves or cabinets.
4 Enclosures and containers
All enclosures and containers used for medium-term and extended-term storage shall meet the requirements
of ISO 18902 and ISO 18916. This includes enclosures and containers that are in either direct or indirect
contact with the prints. Prints may be stored in envelopes or sleeves of paper or plastic, file folders, folding
cartons, boxes and albums, or may be matted. Prints shall be protected from unnecessary use and light
exposure. Prints that are prone to light-induced fading, especially diazo and some colour processes, shall not
be exposed at all.
Generally, prints smaller than 28 cm × 36 cm in size may be stored vertically, but shall be placed between rigid
supports to minimize slumping and curling. Prints 28 cm × 36 cm or larger should be stored horizontally, unless
mounted on rigid supports. Stacks of horizontal prints should be less than 5 cm high to prevent excessive
pressure on prints at the bottom.
Multiple prints, stored within an enclosure or container, shall be oriented with the emulsion sides against back
sides, never emulsion against emulsion.
Suitable plastic enclosure materials are uncoated polyester (polyethylene terephthalate), polystyrene, high-
density polyethylene and polypropylene. Other plastics may be satisfactory, but there has been no extended
experience with such materials. Glassine envelopes and chlorinated, nitrated, or highly plasticized sheeting
shall be avoided. Specifically, cellulose nitrate and polyvinyl chloride are not acceptable. Glassine is not
dimensionally stable when exposed to high relative humidity, although it may meet the other requirements
specified in ISO 18902 and pass the photographic activity test.
Microclimates (sealed enclosures or cabinetry) shall be used where needed in order to maintain the desired
moisture content of the prints where humidity control is inadequate in storage rooms or where cold storage vaults
and units do not have humidity control, and to protect against gaseous and solid atmospheric contaminants.
A variety of sealed vapour-proof housings, containers and cabinetry can provide this protection (as discussed
in Table 1, 7.1.3.2 and Annex H).
The adhesive used for seams and joints shall also meet the requirements of ISO 18902 and ISO 18916. The
filing enclosure shall be constructed so that the seam or joint will be at the edge of the enclosure and not in
contact with the image layer. Photographic-quality gelatine, modified and photographically inert starch, some
acrylic and polyvinyl acetate adhesives and methyl cellulose are suitable adhesives for use with paper.
For maximum life, prints shall be in a clean condition before being placed in storage and shall be inspected
periodically thereafter, as outlined in 9.3.
5 Storage housings
Prints shall be stored in closable storage housings such as drawers or cabinets, in storage cabinets with tightly
fitting doors, or on open shelves when enclosed inside containers. The storage-housing materials shall be
non-combustible, non-corrosive, and chemically inert, e.g. anodized aluminium, stainless steel or steel with
a non-plasticized synthetic resin-powder coating. Wood, pressboard, particle-board, plywood and other such
materials shall be avoided because of their combustible nature and the possibility of their producing active
deteriorating agents as they age.
The finish on the storage housing materials shall be durable and shall not contain substances that can have a
deleterious effect on the stored prints. Finishes containing chlorinated or highly plasticized resins, or solvents
giving off gas from freshly applied finishes can adversely affect the image and base layers on prints. Paints used
on cabinets may give off peroxides, solvents and other contaminants for up to three months after application.
Cabinets made of stainless steel or anodized aluminium are recommended. Metal housing materials that have
been powder-coated (a layer of resin particles that are applied electro-statically to the surface of the metal and
then fused to the surface using heat without the use of chemical solvents) are also recommended.
When air-conditioned individually, storage housings shall be arranged to permit interior circulation of air to all
shelves and drawers holding print containers, so as to provide uniform humidity conditions. Storage housing
located in rooms conditioned in accordance with 7.1 shall be provided with ventilation openings that permit
access of air to the interior. Such openings shall not interfere with the requirements for fire-protective storage
or water protection.
Different types of prints, films and other media may be stored in the same storage room separately from each other.
However, different types of material shall not be stored (interfiled) within the same enclosure or storage container.
6 Storage rooms
6.1 Medium-term storage rooms
Rooms and areas used for print storage should be located in the same area as rooms containing provisions for
inspection and viewing of prints. Good housekeeping is essential. Walls and enclosed air-conditioned spaces
shall be designed to prevent condensation of moisture on interior surfaces and within walls, especially during
periods of low exterior temperatures when the walls may be cooled below the dew point of the air.
Provisions shall be made against damage of prints by fire and by water from floods, leaks and sprinklers, and from
[7][9][12][17]
the steam released from masonry walls during a fire . Storage rooms or vaults should be located above
basement levels where possible. A special storage room separated from the work areas for prints of medium-
term interest generally will not be required, provided the conditions recommended in 7.1.2 are maintained.
6.2 Extended-term storage rooms
For extended-term storage, the requirements of 6.1 shall be met.
In addition, the value of photographic prints kept for long-term purposes makes it advisable to provide a storage
room or vault separate from medium-term storage facilities, temporary storage facilities, offices or work areas.
7 Environmental conditions
7.1 Temperature and humidity specifications for storage
7.1.1 General
See Annexes A, B, C, H and I.
The recommended temperature and relative humidity conditions in Table 1 shall be maintained either within
individual storage housings or within rooms containing such housings.
4 © ISO 2011 – All rights reserved

Table 1 — Maximum temperature and average relative humidity ranges for storage
a
Medium term storage Extended term storage
Relative Relative
Maximum Maximum
ag
Print process humidity humidity
c
temperature temperature
bd
range range
°C % RH °C % RH
e
Black-and-white silver 25 20 to 50 16 30 to 50
Pigment (carbon, carbro)
Dye imbibition (dye transfer)
Silver dye bleach
Dye/silver diffusion transfer (instant)
Diazo
f
Electro-photographic
f
Thermal dye transfer (dye sublimation) 25 20 to 50 2 30 to 50
Chromogenic dye 5 30 to 40
fh
Ink jet (dye or pigment)
a
The values of Table 1 are the required conditions experienced by the photographic material. When micro-climates (housings or
storage containers) are used that establish internal climate conditions, the environment of the exterior room need not necessarily meet
the Table 1 conditions. See Annex H.
b
As discussed in 7.1.3.3, certain gelatine emulsion photographs can be sensitive to RH levels of less than 30 % and can experience
physical changes that can exacerbate existing deterioration such as flaking, cracking and curl. If these materials are present and
RH above 30 % cannot be maintained, then microclimate storage housings or cabinetry shall be used to protect photographs from
extremes in cycling or prolonged excursions below 30 %. Alternatively, a higher RH set point can be selected, e.g. 35 %, when a 5 %
RH fluctuation within any 24-hour period does not exceed the lower RH limit of 30 %.
c
Cycling of temperature shall not be greater than ± 2 °C over any 24-hour period. Some prints can become brittle at low temperatures
and require careful handling when cold to avoid flexing that could cause cracks and image delamination (refer to 7.1.3.3).
d
Cycling of relative humidity shall not be greater than ±5 % RH over any 24-hour period. However, the relative humidity shall not
exceed 50 % RH. If RH cycling in the room cannot be controlled to this level, then microclimate storage housings or cabinetry shall be
used to protect photographs from extremes in cycling or prolonged excursions to either high or low RH.
e
If there is concern about the possibility of silver image deterioration due to atmospheric pollutants, poor quality enclosures,
and/or excessively high temperature and humidity levels, a post-process chemical conversion treatment can be used to provide added
protection (see ISO 18915).
f
The rates of degradation and the potential for physical problems with extremely low temperature and/or low relative humidity
storage is not well known for rapidly changing technologies such as thermal dye transfer (dye sublimation), thermal wax transfer,
electro-photographic, and the many different ink jet image media (dye, pigment, wax) and base media (porous, swellable, plain paper).
Factors such as chemical sensitivity, humidity fastness, and the stability of base materials may have a greater impact on longevity than
thermal stability and light-fastness.
g
Print life expectancy ratings by process type are not provided in this International Standard. For information on print stability, see
Annex I.
h
Some current ink jet prints, especially those utilizing inks made from stable pigment or optimized dyes printed onto stable
supports as recommended by the manufacturer, may have very good image stability at temperatures warmer (up to 16 °C) than the
recommended cold storage temperatures listed for extended-term storage. Where the identification of the type of ink and base cannot
be determined, or where stable ink jet prints may have been interfiled with less stable materials, the colder temperatures listed shall
be used unless prints can be separated by type for storage at different temperatures. The use of non-permanent paper supports or
papers that are not optimized for the particular ink set can also adversely affect the overall stability of the print, requiring storage at
cold temperatures.
7.1.2 Medium-term storage environment
The maximum temperature for medium-term storage shall be 25 °C. Cycling of temperature shall not be greater
than ±5 °C over any 24-hour period, and the peak temperature shall not exceed 30 °C. Some temperature
fluctuation is permitted as long as the relative humidity stays within the specified limits.
The relative humidity of a medium-term storage environment shall be between 20 % and 50 %. Cycling of
relative humidity shall not be greater than ±10 % over any 24-hour period within the specified range (relative
humidity shall not exceed 50 %). The moisture content in prints shall not be greater than the moisture in
equilibrium with these relative humidities. Storing prints at the lower limit of the specified relative humidity
range may cause curling of the prints or physical damage during handling (see 7.1.3.3); prints may need to be
equilibrated to a higher relative humidity prior to use.
7.1.3 Extended-term storage environment
7.1.3.1 Recommended environments for specific print media
A maximum storage temperature of 16 °C with a set point RH within the given range listed in Table 1 shall be
used for black-and-white silver gelatine, silver dye bleach, dye/silver diffusion transfer (instant), dye imbibition
(transfer), pigment (carbon, carbro) and diazo.
Cool storage between 2 °C and 5 °C with a set point RH within the range listed in Table 1 shall be used for
monochrome and multi-colour chromogenic, thermal dye transfer (dye sublimation) and ink jet (see Annex H
for cold storage practices). Excellent keeping behaviour has been obtained by storing colour prints at such low
temperatures.
7.1.3.2 Impact of environment on media longevity
See Annexes C and H.
The rate of most chemical reactions, such as the degradation of bases and discolouration or fading of image
layers, is lowered with decreasing temperature and decreasing relative humidity. Consequently, life expectancy
is increased as either storage temperature or storage humidity is lowered. Added protection may be obtained
for all print types by storage at temperatures lower than the maximum listed in Table 1. Moreover, a lower
storage temperature can compensate for a higher humidity to provide the same life expectancy (see Annex C).
For this reason, several relative humidity/temperature combinations can be used for an extended-term storage
environment as specified in Table 1. Higher relative humidity levels can be employed if the average temperature
is reduced, but the maximum relative humidity shall not exceed 50 %. Cycling of relative humidity shall be no
greater than ±5 % RH over a 24-hour period. Cycling of temperature shall not exceed ±2C over a 24-hour period.
It is difficult to specify in this International Standard what the exact relative humidity and temperature of storage
should be, since they depend upon the value of the prints, the past storage history, the length of time the prints
are to be kept, the size of the storage or cold vaults, the cost of various options and the climate conditions where
the facility is located. The cost/protection ratio is determined by the individual facility. Another very important
factor to consider is the exact mix of photographic materials in the collection, i.e. whether photographic prints,
plates or films are included and whether the materials are new or old. ISO 18934 addresses these issues in
more detail and recommends storage environments for multiple media archives.
The benefit of low-temperature storage is reduced dramatically when prints are taken out frequently and/or for
extended periods of time into higher temperature environments (see Annex C). Prints stored at temperatures
significantly below room temperature will require some warm-up time before they can be used, in order to
prevent the absorption or condensation of moisture on cold surfaces. This warm-up procedure requires that
a vapour barrier be wrapped around the print or its housing prior to removal from the cold temperature area
(see Annex H). Adequate time shall be provided to allow the total volume of prints to approach room temperature
prior to removal of the vapour barrier and use of the prints. The required warm-up time may vary between 1 hour
and 1 day, depending on package size (mass of the contents), degree of package insulation and temperature
differential. The materials shall be allowed to slowly warm above the dew point prior to opening the vapour
barrier. Insulated containers are useful for slowing the warm-up period when there is a large temperature
difference between the cold storage and use conditions, such as with temperatures below 0 °C.
The recommended temperature and relative humidity conditions shall be maintained either within individual
storage housings or within storage rooms containing such housings (see Annex H for cold storage practices and
micro-environment storage). When the control of relative humidity in the macro-environment is not possible,
the micro-environment shall be controlled using an airtight, moisture-proof housing from which as much free
air as possible has been excluded. Prints which might have been exposed to relative humidities above 50 % for
prolonged periods should be conditioned to a lower relative humidity in order to lower their moisture content
prior to being placed in a sealed micro-environment package.
6 © ISO 2011 – All rights reserved

If the relative humidity of the use environment is similar to that of the storage environment, moisture-conditioning
procedures can be reduced or eliminated. In addition, a close match between the two environments reduces
physical stress caused by cycling between storage and use. The time needed to reach moisture equilibration
with a given atmosphere depends on the following factors:
— the hygroscopic nature of the print type (plastic and resin coated paper versus fibre paper);
— the packaging density and volume of material;
— the moisture permeability of enclosure materials and containers;
— the differential between the initial and final moisture content;
— the temperature at which the moisture conditioning occurs.
Free access of air at room temperature will shorten the conditioning time, as will permeable enclosures.
7.1.3.3 Impact of low relative humidity on gelatine emulsion photographs
See Annexes C and D.
Low relative humidities can cause excessive contraction and/or brittleness in gelatine emulsions resulting
in high curl and associated risk of handling damage (cracking). Low relative humidities can cause serious
problems with gelatine emulsion photographs that have existing physical damage such as cracks or flaking
emulsion layers. With such damaged emulsions, a low relative humidity condition can exacerbate lifting along
cracks and existing areas of flaking and curl.
In facilities where such prints are stored, care should be exercised when choosing the relative humidity level
so that items in poor condition (those that are curled or have cracking or delaminating emulsions) are not
physically stressed by low relative humidities in the range of 20 % to 30 %. Cycling between low relative humidity
areas and higher relative humidity areas can exacerbate existing problems. If prints with the above condition
problems are in the collection, the RH set point and RH cycling should be controlled so that excursions below
30 % are avoided. If this cannot be accomplished using HVAC controls, then microclimate storage housings or
cabinetry shall be used to protect photographs from extremes in cycling or prolonged excursions below 30 %.
In general, prints stored tightly packed in boxes or albums, or sleeved in plastic, respond slowly to exterior
short term RH cycling. Loose prints, bare prints or those stored in partially-filled permeable containers may
experience RH changes more quickly and respond accordingly by undergoing curl, and by contraction or strain
on the emulsion (especially along cracks or flaking areas).
Storage at low temperature and/or low relative humidity can embrittle emulsion or image layers, making them
more susceptible to physical damage during handling. Flexing or rough handling may damage brittle prints,
in addition to potentially exacerbating physical problems such as cracking image layers. Because of this, all
such prints, especially those in poor condition, should be handled carefully when in storage at low temperature
and/or low relative humidity. In such cases, it is good practice to restore flexibility prior to use by reconditioning
the prints up to a relative humidity not exceeding 50 %. After use, reconditioning to the recommended humidity
is required before returning the prints to their storage environment. Copies should be made for items that
require frequent or extended use (Annex D). This is especially true since the benefits of increased chemical
stability of photographic materials gained by storage at low temperature or low relative humidity are quickly
mitigated by frequent cycling and prolonged removal to higher temperatures and humidities (Annex C).
7.2 Environmental conditioning requirements
Properly controlled air-conditioning may be necessary for maintaining humidity and temperature within the
specified limits, particularly for extended-term storage where the requirements are more stringent than those
for medium-term storage. Slightly positive air pressure should be maintained within the storage room or vault.
Air-conditioning installations and automatic fire-control dampers in ducts carrying air to or from storage vaults
shall be constructed and maintained on the basis of recommendations contained in appropriate national
[8][13]
standards and regulations . They shall also follow recommendations for fire-resistant file rooms contained
[1][9][17]
in appropriate national standards and regulations . Masonry or concrete walls may release steam from
internally bonded water when heated in a fire. A vapour barrier is required for such vaults, or else sealed
containers shall be used.
Automatic control systems are recommended. They shall be checked frequently with a reliable hygrometer that
has been properly calibrated in order to determine that the humidity limits specified in Table 1 are not being
exceeded. Where air-conditioning is not practical, high humidities may be lowered by electrical refrigeration-type
dehumidifiers and controlled with a humidistat set at the desired humidity level. Desiccants, such as chemically
pure silica gel, may be used provided they are enclosed within units equipped with filters (see 7.3) capable of
removing dust particles 0,3 µm in size and larger, and are controlled to maintain the relative humidity specified
in 7.1. Dehumidification may be required in storage areas such as basements and caves. Because of their
location, these areas have inherently low temperatures and frequently exceed the upper humidity limit.
Humidification is necessary if the prevailing relative humidity is less than that recommended in 7.1, or if prints
suffer physical damage, such as curling or delamination of the image layer from the support, due to increased
brittleness or dryness at lower relative humidities. If humidification is required, a controlled humidifier should
be used. Water trays or saturated chemical solutions shall not be used because of the serious danger of over-
humidification.
7.3 Air purity
See Annexes E and G.
Solid particles can abrade prints or react with the image. They shall be removed by mechanical filters from air
supplied to housings or rooms used for extended-term storage. These mechanical filters should preferably be
of the dry media type, having an arrestance rating of not less than 85 %, as determined by tests contained in
[10][14][16]
appropriate national standards and regulations . Filters shall be of a non-combustible type, meeting
[10][14]
the construction requirements of appropriate national standards and regulations .
Gaseous impurities such as sulphur dioxide, hydrogen sulphide, peroxides, ozone, ammonia, acidic fumes,
solvent vapours and nitrogen oxides cause deterioration of the print support or degradation of the image in
some prints, especially dye-based ink jet printed on porous coated supports. Suitable washers or absorbers
can remove them from the air. Because ozone is especially harmful to ink jet images, exposure to it shall be
minimized through the use of air filtration and/or layers of enclosures and containers. Where practical, storage
of prints in sealed enclosures, containers and storage housings in accordance with Clauses 4 and 5 will afford
adequate protection.
Since paint fumes can be a source of oxidizing contaminants, prints should be removed from either an extended-
term or medium-term storage area for a 3-month period when the area is freshly painted. The use of zero VOC
(Volatile Organic Compound) paints can reduce the wait period to the time needed for the paint to fully dry.
7.4 Light, use, and display
See Annexes D and I.
Normally, extended-term keeping conditions for prints which have enduring and permanent value specify
infrequent use and storage under dark conditions. This is recommended practice as light can be detrimental to
some images and handling can inflict physical damage.
However, it is realistic to assume that prints will be viewed or displayed at some point in their lifetime, otherwise
[11][15]
keeping these materials would be pointless . The lifetime of prints on display is beyond the scope of
this International Standard due to the many types of historic and modern print technologies, rapidly changing
product developments, and the many variables that affect print display life (see Annex I). Long-term display
is not recommended for prints since the image material can fade, darken or shift colour balance as a result
of exposure to light and air-borne contaminants or due to environmental conditions that do not match those
specified in this International Standard. The base material can also undergo degradation in display conditions.
Many institutions have developed strict exhibition policies that specify light levels, cumulative light exposure
limits and environmental conditions. Institutions also employ micro-environmental display packages to reduce
exposure to atmospheric contaminants, relative humidity extremes, and/or cycling humidity. Institutions may
also monitor their displayed prints using colorimetry or densitometry in order to intervene before severe image
degradation has occurred.
8 © ISO 2011 – All rights reserved

The quality of frame and framing materials can greatly impact the stability of prints. Requirements for these
materials are specified in ISO 18902. Annex D discusses in detail the issue of frequent use and display of
prints which have permanent value, and recommends the creation of copies or facsimiles for frequently used
or displayed prints which have enduring or permanent value so that the original can be maintained in ideal
environments appropriate for their long-term preservation.
8 Fire-protective storage
See Annex F.
Enclosure materials for fire-resistant storage shall be sufficiently fire-resistant so that they will not ignite or
develop reactive fumes after heating for 4 hours at 150 °C in the package that is to be stored. Many enclosure
materials will melt or become badly distorted at this temperature. Do not use enclosures that deform or melt to
the extent that the print cannot be removed from the enclosure or is permanently damaged by the enclosure.
For protection against fire and associated hazards, prints shall be placed in closed containers in either
[7][12]
fire-resistant vaults or insulated record containers (Class 150) . If fire-resistant vaults are used, they
shall be constructed in accordance with recommendations contained in appropriate national standards and
[9][17]
regulations , with particular care taken for protection from steam. When the quantity of prints is not too
great, insulated record containers (Class 150) conforming to appropriate national standards and regulations
may be used. An interior temperature of 66 °C and an interior relative humidity of 85 % shall not be exceeded
when carrying out a fire-exposure test lasting from 1 hour to 4 hours, depending on the classification of the
record container. Insulated record containers shall be situated on a ground-supported floor if the building is not
fire-re
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