Overview
ISO 18924:2013 - "Imaging materials - Test method for Arrhenius-type predictions" specifies an accelerated test method to predict certain physical and chemical property changes of imaging materials using Arrhenius-type analysis. The standard is focused on predicting optical-density (D) loss or gain, support degradation (for example acetic acid generation from cellulose acetate), and density changes caused by residual couplers, residual processing chemicals in silver materials, or temperature effects on thermally processed silver images. It is intended for the Arrhenius portion of related ISO imaging stability standards.
Key topics and technical requirements
- Arrhenius methodology: Measure time-to-change at multiple elevated temperatures, then plot the logarithm of time versus the reciprocal of absolute temperature to extrapolate lifetimes at lower temperatures.
- Minimum test conditions: A meaningful prediction requires testing at a minimum of four temperatures to allow statistical evaluation and avoid biased extrapolation.
- Humidity control: Tests can be run in either constant relative humidity (free-hanging) or sealed-bag (constant moisture content) modes. If humidity effects are relevant, experiments at different RH levels (at least 10% RH apart, preferably 20% RH) are required.
- Sealed-bag vs free-hanging: Sealed-bag tests simulate trapped volatiles (e.g., acetic acid), whereas free-hanging simulates ventilated storage. Pre-equilibration and RH compensation for sealed bags are necessary because RH inside sealed bags rises with temperature.
- Data treatment and limits: Only linear portions of Arrhenius plots should be extrapolated. Nonlinear behavior can indicate multiple reaction pathways or irrelevant high-temperature reactions; Annexes detail limitations and examples.
- Experimental steps: Prepare specimens, take initial readings, incubate at multiple temperatures, measure properties over time, determine times to predetermined changes, plot/log and extrapolate.
Applications and users
ISO 18924 is used for:
- Predicting image fading (chromogenic, diazo, dye-diffusion, silver dye-bleaching)
- Assessing support degradation (cellulose acetate, paper tensile properties)
- Evaluating effects of residual chemicals and thermal processing on image stability
Primary users:
- Photographic and film manufacturers
- Conservation scientists and archives
- Testing laboratories and quality control groups
- Film preservationists and collection managers
Related standards
Keywords: ISO 18924, Arrhenius, imaging materials, accelerated aging, optical density, photographic dye fading, sealed-bag testing, free-hanging testing, relative humidity, support degradation.
