Overview
EN ISO 7668:2021 (ISO 7668:2021) specifies standardized methods for measuring specular reflectance and specular gloss of anodic oxidation coatings on flat samples of anodized aluminium and its alloys. The standard defines four main geometries - 20° (Method A), 45° (Method B), 60° (Method C) and 85° (Method D) - plus an additional 45° narrow‑acceptance-angle method (Method E). It is intended mainly for clear anodized surfaces and can be applied to colour‑anodized aluminium only when comparing similar colours.
Key Topics
- Measurement geometries: Procedures for 20°, 45°, 60° and 85° specular angles; Method E uses a narrow acceptance angle at 45°.
- Specular reflectance vs specular gloss: Definitions based on luminous flux in the specular direction; gloss is referenced to polished black glass.
- Reference standard: Polished black glass (refractive index 1.567 at 546.1 nm) is assigned a gloss value of 100 for the four geometries.
- Apparatus and optical requirements: Use of reflectometers, defined light sources, photoelectric detectors and filters to approximate the CIE spectral luminous efficiency V(λ) weighted for C or D65 illuminants.
- Influence of geometry and aperture: The standard explains that specular properties vary with measurement angle and acceptance aperture; anodized aluminium can show complex behaviour due to partial reflection from both the film surface and underlying metal.
- Calibration and reporting: Requirements for calibration (working and reference standards), zero checks, expression of results and elements to include in the test report.
Applications
- Quality control and acceptance testing in anodizing plants, surface‑treatment laboratories and material inspection labs.
- Specification and comparison of surface appearance for architectural, automotive and industrial aluminium components where reflectance or gloss affects aesthetics or performance.
- R&D and process optimization to evaluate the effect of anodizing parameters on surface specular properties.
- Useful for manufacturers, coating specifiers, test laboratories, and procurement teams who require consistent, comparable measurements of anodized aluminium finish.
Related Standards
- ISO 7583 - Anodizing of aluminium and its alloys - Terms and definitions
- ISO/CIE 11664-1 and ISO 11664-2 - Colorimetry and standard illuminants
- CIE Publication No. 15 - Colorimetry
EN ISO 7668:2021 (endorsed by CEN) supersedes the 2018 edition and is maintained by ISO/TC 79 in collaboration with CEN/TC 132. Keywords: anodizing, anodized aluminium, specular reflectance, specular gloss, reflectometer, measurement angles, ISO 7668:2021, Method A B C D E.
