ISO 18936:2020

Overview

ISO 18936:2020 - "Imaging materials - Processed colour photographs - Methods for measuring thermal stability" defines standardized test methods for assessing the long-term dark storage stability (thermal stability) of processed colour photographic images. Applicable to traditional photographic systems (chromogenic, silver dye-bleach, dye transfer, dye-diffusion-transfer “instant”) and to digital outputs (dry- and liquid-toner electrophotography, thermal dye transfer / dye sublimation, and inkjet), the standard provides procedures for accelerated ageing tests that support predictions of likely image change over time.

Key topics and technical requirements

• Scope and applicability: Test methods cover a broad range of photographic and digital print technologies for dark storage stability evaluation.
• Test principles: Uses accelerated thermal ageing (Arrhenius-type approach) to extrapolate long-term behaviour from elevated-temperature tests; empirical confirmation is required for validity.
• Sample preparation: Guidance on target selection, use of replicates and reference samples to ensure statistically meaningful results.
• Holding and measurement conditions: Specifies controlled temperature and relative humidity parameters, notes effects of humidity and atmospheric pollutants, and highlights sensitivity of low glass transition temperature products.
• Test methods: Two principal exposure configurations:
  • Free-hanging method at constant relative humidity
  • Sealed bag method to maintain constant moisture content
• Measurement endpoints: Monitor changes in density, colour balance (differential fading of cyan/magenta/yellow), stain formation and other visible degradations.
• Reporting requirements: Defines what must be recorded in a test report (general conditions, specimen details, equipment, measured results); computational details for Arrhenius predictions are now in ISO 18944.
• Caveats: Notes that some materials exhibit atypical behaviour (e.g., instant prints, some chromogenic and dye-bleach products) and that elevated conditions (above ~60% RH or very high temperatures) can produce non-representative degradation.

Applications and who uses it

ISO 18936:2020 is used by:

• Manufacturers of photographic papers, films and printing inks/toners for product development and quality assurance.
• Conservation scientists, museums and archives assessing storage strategies and expected lifetimes for collections.
• Testing laboratories performing accelerated ageing and permanence testing.
• Print service providers and color technologists evaluating output stability for client specifications.

Practical uses include validating materials for long-term preservation, setting storage recommendations (temperature/RH), and comparing product stability across media and processes.

Related standards

• ISO 18944 - Arrhenius-type predictions and computational methods (referenced for calculations)
• ISO 18924 - Test method for Arrhenius-type predictions
• ISO 18941 - Ozone gas fading stability for colour reflection prints
• ISO 18913 - Permanence - Vocabulary
• ISO 5-3 / ISO 5-4 / ISO 13655 - Density and colorimetric measurement methods

Keywords: ISO 18936:2020, thermal stability, dark storage stability, colour photographs, accelerated ageing, Arrhenius, inkjet permanence, chromogenic, photographic preservation, museum archives.