Overview
ISO 2135:2017 - Anodizing of aluminium and its alloys - Accelerated test of light fastness of coloured anodic oxidation coatings using artificial light - specifies a laboratory procedure to assess the light fastness (colour stability) of coloured anodic oxidation coatings on aluminium using artificial light sources. It is designed as an accelerated, repeatable quality-control test for coatings whose outdoor light fastness has already been established. The method defines apparatus, specimen preparation, exposure conditions, visual and instrumental evaluation, and reporting requirements.
Key topics and requirements
- Scope and limitations: Applicable to coloured anodized coatings produced by any process; not suitable for coatings with an outdoor-established light fastness number below 6.
- Principle: Calibrate the apparatus using standard cloth samples (light fastness number 6) to define an exposure cycle. Expose test specimens until a colour change equals grade 3 of the grey scale (~25% loss of colour).
- Apparatus and light sources: Acceptable sources are xenon-arc lamps, open-frame carbon-arc, or enclosed carbon-arc lamps (specifications in Annex A). Typical cycle times cited: ~300 h for xenon-arc and ~150 h for carbon-arc (for the standard cloth).
- Specimen preparation: Sample from a representative flat area (avoid edges); standard specimen size ~150 mm × 70 mm; clean and mask part of the surface to detect colour change.
- Exposure conditions: Maintain black panel temperature at (63 ± 3) °C (or (50 ± 3) °C by agreement); ensure constant irradiance, distance and ambient conditions; rotate specimens or relocate to equalize exposure.
- Assessment:
- Visual: assign a light fastness number based on the number of cycles needed to reach grey-scale grade 3 (Table maps cycles to numbers 6–>10).
- Instrumental: measure colour difference as ΔE* (ISO 4582) and, if required, gloss retention (ISO 7668).
- Reporting: Must reference ISO 2135:2017 and include material, finishing, light source, test results, deviations and date.
Applications
- Routine quality control and batch acceptance for anodized aluminium finishes.
- Comparative testing in R&D and process optimization for colouring and sealing steps.
- Prequalification of finishes for architectural façades, curtain walls, signage, consumer goods and transport components where long-term colour stability is important.
- Useful for testing laboratories, anodizers, coating formulators, specifiers and façade engineers.
Related standards
Keywords: ISO 2135:2017, anodizing of aluminium, light fastness, coloured anodic oxidation coatings, accelerated test, xenon-arc, carbon-arc, grey scale, ΔE*, gloss retention.