ISO 21066:2018

Overview

ISO 21066:2018 specifies the Resazurin (Rz) ink test for the qualitative and semiquantitative assessment of the photocatalytic activity of flat, smooth, non‑macroporous surfaces under artificial ultraviolet (UVA) irradiation. The method classifies materials as below, within, or above the applicable range of the test and, for samples within range, provides a semiquantitative evaluation based on the time required for a colour change in a deposited Rz ink film.

Key SEO phrases: ISO 21066:2018, resazurin ink test, photocatalytic activity, Rz ink, UVA irradiation, fine ceramics.

Key topics and technical requirements

• Test principle: Photocatalysed reduction of resazurin in an ink film, monitored as a blue→pink colour change under defined UVA irradiance.
• Sample preparation: Typically 25 mm × 25 mm samples, cleaned and coated uniformly with Rz ink using a K‑bar (standard K‑bar number 3 giving ~24 µm wet film thickness).
• Qualitative method (three samples):
  • Three identically coated samples are irradiated simultaneously.
  • Determine average irradiation end time (t_end,av).
  • Classification thresholds: t_end,av < 1.5 min = above range; 1.5–45 min = within range; >45 min = below range.
  • If above range, repeat at reduced irradiance before proceeding.
• Semiquantitative method (eight samples):
  • Eight samples irradiated and imaged periodically.
  • Digital RGB image analysis of the ink centre yields a normalized red parameter R(t).
  • Calculate time to reach 90% of the maximum R change (ttb(90)) for each sample and derive median and dispersion metrics for activity ranking.
• Instrumentation: Defined UVA light source and radiometer (see ISO 10677), coating device (K‑bar), digital imaging device and analysis software.
• Limitations: Not applicable for visible‑light photocatalytic activity nor direct measurement of air/water purification, self‑cleaning or disinfection performance (although correlations may exist).

Applications and users

• Practical for manufacturers and quality-control labs testing photocatalytic glass, tiles, paints, awnings and other flat photocatalytic surfaces.
• Useful for product development, batch comparison, incoming materials inspection, and R&D where a rapid surface‑activity assay under UVA is required.
• Beneficial to standards bodies, testing laboratories, ceramic and coatings industries, and researchers benchmarking photocatalytic surface activity.

Related standards

• ISO 10677 - Ultraviolet light source specifications for testing photocatalytic materials.
• ISO 22197‑1 and ISO 20507 - referenced definitions and terminology relevant to photocatalysis and photocatalytic materials.

This standard provides a reproducible, image‑based approach to assess and compare surface photocatalytic activity under controlled UVA conditions, supporting consistent product evaluation and development.