Overview
ISO 18949:2019 - "Imaging materials - Reflection colour photographic prints - Method for testing stability under low humidity conditions" specifies standardized test methods to evaluate how reflection colour photographic prints respond to low relative humidity. The method focuses on measurable changes in image appearance (primarily substrate yellowing) and includes visual assessment of humidity-related physical damage such as curl, cockle, cracking, or delamination. The standard is intended for comparative laboratory testing (not for making time‑based lifetime claims).
Key topics and requirements
- Test goal: Quantify image appearance change caused by sustained low relative humidity (expressed as CIELAB ΔE* values) and report observed physical damage.
- Sample preparation: Print an eight‑patch test target at controlled ambient printing conditions (23 °C ± 2 °C, 50 % RH ± 10 % RH). Condition samples 24 h ± 2 h at the same environment with unrestricted airflow before exposure.
- Humidity exposure: Fixed low‑humidity exposure specified (example condition: 25 °C at 10 % RH for 12 months). Equipment and environment control, calibration and operational uniformity are required.
- Colorimetric measurement: Use CIE colorimetry conforming to ISO 13655 (M2 conditions; M1 optional). Measure Lab* of the eight patches before and after exposure and calculate individual ΔE*ab for each patch.
- Data analysis & reporting: Report measured deterioration (average ΔE* and individual ΔE* values) and visual observations of physical degradation. Tests are for comparative stability and screening; they must not be used alone to claim absolute print lifetimes.
- Accuracy considerations: Address measurement uncertainty, operational control/ fluctuation/uniformity, and calibration per referenced documents.
Applications and users
- Who uses ISO 18949:2019: Print material developers, ink manufacturers, paper and media producers, quality assurance labs, conservation scientists, and imaging R&D teams.
- Practical uses:
- Screen inkjet papers, dye diffusion, and silver‑halide prints for susceptibility to low‑humidity substrate yellowing.
- Compare formulations and coatings for humidity fastness.
- Support product development, internal QA and controlled comparative testing of humidity‑related failure modes.
- Inform conservation decisions where prints may be stored in low‑RH environments (cold climates, heated indoor air, air‑conditioned dry climates).
Related standards
- ISO 13655 - Spectral measurement and colorimetric computation (referenced for colorimetry)
- ISO 18913 - Imaging materials - Permanence - Vocabulary
- ISO/TR 18931 - Recommendations for humidity measurement and control
- ISO 18941 - Test method for ozone gas fading stability
- ISO 18946 - Testing stability under high relative humidity
Keywords: ISO 18949:2019, low humidity testing, reflection colour photographic prints, substrate yellowing, ΔE* colorimetry, ISO 13655, humidity exposure, print stability.
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