ISO 18909:2022 pdf – Photography — Processed photographic colour films and paper prints — Methods for measuring image stability.
1 Scope This document describes test methods for determining the long-term dark storage stability of colour photographic images and the colour stability of such images when subjected to certain illuminants at specified temperatures and relative humidities. This document is applicable to colour photographic images made with traditional, continuous- tone photographic materials with images formed with dyes. These images are generated with chromogenic, silver dye-bleach, dye transfer, and dye-diffusion-transfer instant systems. The tests have not been verified for evaluating the stability of colour images produced with dry- and liquid-toner electrophotography, thermal dye transfer (sometimes called dye sublimation), ink jet, pigment-gelatin systems, offset lithography, gravure and related colour imaging systems. If these reflection print materials, including silver halide (chromogenic), are digitally printed, refer to ISO 18936, ISO 18941, ISO 18946, and ISO 18949 for dark stability tests, and the ISO 18937 series for light stability tests. This document does not include test procedures for the physical stability of images, supports or binder materials. However, it is recognized that in some instances, physical degradation such as support embrittlement, emulsion cracking or delamination of an image layer from its support, rather than image stability, will determine the useful life of a colour film or print material. 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 5-2, Photography and graphic technology — Density measurements — Part 2: Geometric conditions for transmittance density ISO 5-3, Photography and graphic technology — Density measurements — Part 3: Spectral conditions
Stability data obtained from a colour material processed in certain processing chemicals shall not be applied to the colour material processed in different chemicals, or using a different processing procedure. Likewise, data obtained from test specimens shall not be applied to colour materials that have been subjected to post-processing treatments (e.g. application of lacquers, plastic laminates or retouching colours) that differ from the treatments given to the test specimens. 4.3 Densitometry Image density shall be measured with the spectral conditions specified for Status A densitometry (transparencies and reflection prints) and for Status M densitometry (negatives) as described in ISO 5-3. Transmission density, D T , (90° opal; S: < 10°; s) shall be measured with an instrument complying with the geometric conditions described in ISO 5-2. Reflection density, D R , (40° to 50°; S: 5°; s) shall be measured as described in ISO 5-4. One of the problems encountered in densitometry is the instability of the measuring devices, especially during the course of long-term tests. Some of the components of densitometers that can change appreciably with age, as well as from one unit or batch to another, are the optical filters, the light sensors and the lamps. For example, the filters in many modern densitometers will deteriorate with age and shall be replaced periodically, often within 2 years to 3 years. However, replacement filters of the same type frequently do not exactly match the original filters in spectral transmittance characteristics. Such changes in transmittance will cause unequal changes in the measured density values of dyes having different spectral absorption properties. One way of dealing with such problems in a densitometer system is to keep standard reference specimens of each test product sealed in vapour-proof containers and stored at −18 °C or lower.
4.6 Method of correction of density measurements for d min changes 4.6.1 General The areas of minimum density of many types of colour photographs change with time during dark storage, and generally to a lesser extent also change on prolonged exposure to light during display or projection. Such changes most commonly take the form of density (stain) increases, usually yellowish in colour. However, some materials, under certain conditions, may exhibit a loss in minimum density; e.g. colour negatives in dark storage. For the purposes of this document, changes in minimum density as measured in d min patches, whether increases or losses, are assumed to have occurred equally at all density levels. Therefore, in order to determine accurately the amount of dye-fading that has taken place during testing or during storage and display, it is necessary to take into account the change in the d min value (see Table 2).