ISO 18946:2023

Overview

ISO 18946:2023 specifies laboratory test methods for evaluating the humidity fastness of reflection colour photographic prints. It defines controlled procedures to assess changes in image appearance - colour, tone and loss of sharpness - caused by exposure to elevated relative humidity (RH). The standard is particularly applicable to dye-based technologies where colorants diffuse in image-receiving layers (for example inkjet or dye diffusion processes) or to prints on uncoated fibrous paper. It excludes humidity effects such as mould/mildew growth and physical damage from humidity cycling (curl, cracking, delamination).

Key topics and requirements

• Test targets and sample preparation
  • Use of a defined checkerboard test pattern (printed at (23 ± 2) °C and (50 ± 10) % RH).
  • Sample conditioning: (24 ± 2) h at (23 ± 2) °C and (50 ± 5) % RH with unrestricted airflow.
• Humidity exposure methods
  • Method A (fixed condition): 25 °C and 85 % RH for a recommended 4 weeks (options: 1, 2 or 8 weeks) to quantify deterioration.
  • Method B (multi-level): 25 °C for 2 weeks at three or more RH levels chosen from 60–95 % RH to identify onset of visible change.
• Measurement and analysis
  • Colorimetric measurements using CIELAB (ISO/CIE 11664‑4) before and after exposure.
  • Calculation of colour difference ΔE for checkerboard patches to quantify blur, colour fringing and tone shifts.
  • Reporting requirements specify sample information, test conditions and ΔE results; cautions against using data for life-expectancy claims.
• Equipment and control
  • Requirements for controlled humidity chambers, sensor calibration, and consideration of operational uniformity and fluctuation.

Practical applications and users

• Who benefits:
  • Printer and ink manufacturers validating humidity stability of materials and processes.
  • Materials developers optimizing substrates and coatings for humidity resistance.
  • Quality assurance and test laboratories performing standardized comparative testing.
  • Cultural heritage professionals and archives assessing risks for displayed or stored colour prints.
• Practical value:
  • Provides reproducible laboratory data to compare humidity sensitivity of colour hardcopy technologies.
  • Helps identify humidity thresholds where visible deterioration begins, supporting product guidance and storage/display recommendations.
• Important caveat: results are for comparative or failure-mode reporting and must not be used alone for public lifetime claims.

Related standards

• ISO 18949 - Imaging materials: low humidity testing (complements ISO 18946)
• ISO 18913 - Permanence vocabulary
• ISO/TR 18931 - Humidity measurement and control recommendations
• ISO 13655, ISO/CIE 11664-4 - Colorimetry and spectral measurement
• ISO 18941 - Ozone gas fading stability

Keywords: ISO 18946:2023, humidity fastness, imaging materials, reflection colour photographic prints, inkjet, dye diffusion, relative humidity, CIELAB, ΔE, checkerboard pattern.