|
Ref. No.: ISO/ R 421 - 1965 (E)
IS0
I NT ERN AT I O NA L
ORGANIZATION FOR STAND AR D I Z AT I O N
IS0 RECOMMENDATION
R 421
METHOD FOR INDICATING THE STABILITY OF THE IMAGES
OF PROCESSED BLACK-AND-WHITE FILMS, PLATES AND PAPERS
1st EDITION
March 1965
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
---------------------- Page: 1 ----------------------
BRIEF HISTORY
The IS0 Recommendation R 421, Method for Indicating the Stability of the Images
of Processed Black-and- White Films, Plates and Papers, was drawn up by Technical
Committee ISO/TC 42, Photography, the Secretariat of which is held by the American
Standards Association, Inc. (ASA).
Work on this question by the Technical Committee began in 1956 and led, in 1958,
to the adoption of a Draft IS0 Recommendation.
In August 1961, this Draft IS0 Recommendation (No. 396) was circulated to all the
IS0 Member Bodies for enquiry. It was approved, subject to a few modifications of an
editorial nature, by the following Member Bodies :
Belgium Germany Romania
Brazil Italy Sweden
Canada Japan Switzerland
Chile Netherlands United Kingdom
France New Zealand U.S.A.
U.S.S.R.
No Member Body opposed the approval of the Draft.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in March 1965, to accept it as an IS0 RECOMMENDATION.
-2-
---------------------- Page: 2 ----------------------
I
IS0 / R 421 - 1965 (E)
IS0 Recommendation R 421 March 1965
METHOD FOR INDICATING THE STABILITY OF THE IMAGES
OF PROCESSED BLACK-AND-WHITE FILMS, PLATES AND PAPERS
1. SCOPE
1.1 General scope
This IS0 Recommendation specifies test methods for indicating the relative stability of the
images of processed films, plates and papers, as conditioned by the internal factors resulting
from processing. It applies only to processed photographic materials containing silver
particles in an organic colloid layer, and not to dye images, tinted, toned or intensified
photographs.
1.2 Purpose of the three test methods
The scope of the three test methods given is as follows:
Test Effect
Test for effect of thiosulphate Fading or darkening due to chemical reaction of
(hyposulphite) (see clause 3.1) residues of thiosulphate or other treating agents
Test for light stability Darkening due to action of light on residual silver
(see clause 3.2) compounds
Test for effect of silver compounds Discoloration due to chemical action on residual
(see clause 3.3) silver compounds.
Appropriate criteria are given for archival and non-archival cases respectively. All three
tests are necessary to characterize image stability, but any one test may be useful for a
particular purpose.
Nom-The qualitative criteria for archival and non-archival cases given in the methods of this IS0 Recom-
mendation are not specifications per se for materials tested in the respective cases.
2. GENERAL
2.1 Factors affecting stability
Deterioration of the image of processed photographic materials is controlled by factors
which may be classified as internal and external.
2.1.1 Internal factors. The internal factors determine the stability and are the subject of the test
methods. They include the state of division of the silver, the form of the image (for
example, narrow lines or small spots of low density in a field of high density, or the
converse), and a group of factors governed by the processing treatment, the presence
of protective substances, the content of uncombined fixing or " stabilizing " agents,
such as the thiosulphates, the acidity and the residual silver compounds in the processed
material. Instability of the base or other layers may be an internal factor in so far as
decomposition in any of them may yield products which stain or attack any part of the
image.
-3-
---------------------- Page: 3 ----------------------
IS0 / R 421 - 1965 (E)
2.1.2 External factors. Some of the most common external factors are the conditions of tem-
perature and humidity, the intensity and quality of light, or other radiation to which the
photographic material is exposed, the presence of active gases in the atmosphere and the
time of exposure to any of these.
The durability of the photographic record when subjected to weathering, biological
attack or mechanical wear is not within the scope of this IS0 Recommendation.
2.2 Purpose of test
The test methods are intended to evaluate the internal factors by subjecting representative
samples of the processed materials to some of the external factors in a severe but controlled
degree.
2.3 Effect according to type of process: fixing or ‘‘ stabilizing ”
Following completion of photographic development, the photographic material is subjected
either to fixing and washing or to a so-called “ stabilizing ” treatment to impart the required
resistance to darkening, discoloration and fading during subsequent use or storage.
2.3.1 When the fixing and washing process is employed, the object is to convert the unused
silver salt to a soluble complex which, along with the fixing chemicals, will then be
removed by thorough washing, so as to assure a relatively high degree of stability.
2.3.2 In contrast, the “ stabilizing ” processes usually consist of bathing the developed
material in a solution containing, for example, thiosulphate, thiourea or thiocyanate,
to convert the unused silver salt to a comparatively stable chemical complex. In some
of these processes, half or more of the silver compounds are removed from the photo-
graphic material. Drying follows, either without any intermediary washing or, at the
most, with a superficial rinse. Generally speaking, the degree of stability attainable by
“ stabilization ” is less in one respect or another than that attainable with the more
usually employed fixing and washing processes.
2.4 Effect of excess thiosulphate or tetrathionate
The possible extent of fading which results from reactions involving thiosulphate and image
silver, with the consequent conversion of the latter to silver sulphide, is dependent, among
other things, upon the relative quantities of metallic silver and excess thiosulphate, and the
state of subdivision of the silver. Conversion to silver sulphide does not necessarily render
the image useless, unless legibility, image detail or aesthetic quality is too much impaired.
The amount of such fading or discoloration allowable in a negative or print will depend
somewhat upon the use for which the materia1 is intended. Thus a slight discoloration may
be seriously objectionable in pictorial matter, especially if it is uneven, while extensive
sulphiding of a line image may be inconsequential, if legibility is not lost.
The rate at which the actual chemical conversion takes place varies widely, not only with the
factors mentioned above, the form of the image, the presence of protective material, the
acidity or alkalinity and the relative quantities of free thiosulphate and sulphite, but also
with temperature and humidity. It is impossible to assign a definite figure for the expected
life of a given sample of processed material on the basis of any one factor, such as free
thiosulphate content. However, the relative stability of the image can be indicated from the
results of empirical accelerated tests on samples of typical image matter.
-4-
---------------------- Page: 4 ----------------------
IS0 / R 421 - i965 (E)
Methods for determining the thiosulphate in processed photographic film and papers
respectively are given in IS0 Recommendation R 41 7, Method for deterniining tiîiosulphate
and tetratlzionate in processedblack-and-,vhite photographicfilm, plates andpupers. The method
of Part II of this IS0 Recommendation also determines tetrathionate (for example, sodium
tetrathionate (Na,S,O,)), which may result from mild oxidation of thiosulphate and which,
during storage, can effect conversion of the silver image to silver sulphide in a manner
analogous to soluble thiosulphate.
2.5 Effect of other fixing or '' stabilizing " agents
Fading effects may be produced when the silver grains are
...