Overview
ISO 7668:2021 specifies standardized methods for the measurement of specular reflectance and specular gloss of anodized aluminium and its alloys. It defines test geometries at 20°, 45°, 60° and 85° (Methods A–D) and an additional 45° narrow‑acceptance method (Method E). The standard is intended mainly for clear anodized surfaces and can be applied to colour‑anodized aluminium when comparing similar colours. ISO 7668:2021 helps produce reproducible, comparable reflectometer and glossometer results for quality control, specification and product development.
Key Topics and Requirements
- Scope and purpose
- Measurement methods for flat anodic oxidation coatings using specified reflectometer geometries.
- Emphasis on repeatability and intercomparability of results.
- Methods A–E
- Method A: 20° geometry
- Method B: 45° geometry
- Method C: 60° geometry
- Method D: 85° geometry
- Method E: 45° with narrow acceptance angle for refined specular reflectance
- Geometric conditions
- Precise incident and receptor angle tolerances (±0.1°) and aperture dimensions to avoid vignetting.
- Guidance on lens focal lengths and aperture calculations.
- Apparatus and optics
- Polychromatic light source, receptor housing with aperture and photoelectric cell, sensitivity control and meter with 1% full-scale accuracy.
- Use of spectral sensitivity approximating the CIE luminous efficiency function (V(λ)) when required.
- Standards and reference materials
- Use of black glass reference (assigned gloss 100) and glass prism for Method E.
- Working standards and zero‑point checks; Annex A gives black glass data.
- Calibration, measurement and reporting
- Procedures for apparatus preparation, calibration, measurement of specular reflectance and gloss, expression of results and required test report items.
Applications and Who Uses It
- Quality control in anodizing plants to monitor surface appearance and consistency.
- Coating and surface engineers evaluating anodic film optical properties.
- Product developers and specifiers (architects, building façade designers, automotive and aerospace finish engineers) requiring reproducible gloss/reflectance data.
- Testing laboratories and third‑party certification bodies conducting comparative or compliance testing of anodized aluminium.
- Practical tip: measure multiple angles for anodized aluminium because its double‑reflection behavior can make reflectance angle‑dependent; bright mirror finishes are commonly measured at 45° or 20°.
Related Standards
- ISO 7583 - Anodizing of aluminium: Terms and definitions
- ISO/CIE 11664-1 - Colorimetry: CIE standard colorimetric observers
- ISO 11664-2 - Colorimetry: CIE standard illuminants
- CIE Publication No. 15 - Colorimetry
Keywords: ISO 7668:2021, anodizing of aluminium, specular reflectance, specular gloss, anodic oxidation coatings, reflectometer, glossometer, measurement angles 20° 45° 60° 85°.