Overview
ASTM E2175-01(2021), Standard Practice for Specifying the Geometry of Multiangle Spectrophotometers, provides a structured approach for manufacturers, users, and specifiers to precisely define the angular and spatial measurement conditions of multiangle spectrophotometers. These instruments play a critical role in objectively quantifying the appearance of gonioapparent materials-materials whose optical appearance changes with angle, such as metallic paints, plastics, certain textiles, and materials containing pearlescent or interference pigments.
This standard highlights best practices for the geometric description and measurement setup of spectrophotometers used in industries like automotive manufacturing, material supply, and coatings, where accurate color and appearance evaluation is essential.
Key Topics
- Geometry Specification: The practice provides detailed guidelines for specifying the angular orientation (influx and efflux angles), spatial configuration, and angular selectivity of multiangle spectrophotometry measurements.
- Instrument Configurations: Defines four key geometric configurations for measurement:
- Uniplanar
- Annular
- Circumferential
- Diffuse
- Sampling Aperture: Details on selecting and defining the sampling aperture (either circular or rectangular) and its spatial position in the measurement setup for reproducibility and accuracy.
- Directional Illumination and Viewing: Differentiates between standard conical/pyramidal illumination versus diffuse setups, ensuring clear reporting and standardization.
- Angular Tolerances and Selectivity: Offers methods to specify and maintain tolerances for angular positions, uniformity of illumination, and measurement repeatability.
Applications
ASTM E2175 is widely applicable in contexts where the visual appearance of a material depends strongly on observation and illumination angles. Notable industry sectors include:
- Automotive Manufacturing: For routine measurement and quality control of metallic and pearlescent paints and finishes, ensuring consistent appearance under varying viewing angles.
- Material Suppliers and Coatings Producers: Enables suppliers to provide objective, standardized characterization data for metallic or specialty effect pigments to their customers.
- Plastic Manufacturing: Used for assessing colored and effect-laden plastics that show color shift with angle, important for consumer electronics, packaging, and decorative objects.
- Research and Development: Laboratories and institutions developing or testing new materials needing rigorous, comparable appearance data.
- Quality Assurance: Ensures that all stakeholders use consistent methods to measure and specify the visual characteristics of gonioapparent materials, reducing disputes and variability in results.
Related Standards
ASTM E2175 references and complements several other ASTM standards for appearance and color measurement:
- ASTM E284 – Terminology of Appearance
Supports standardized vocabulary for describing appearance attributes.
- ASTM E308 – Practice for Computing the Colors of Objects by Using the CIE System
Provides guidance for colorimetric calculations.
- ASTM E1164 – Practice for Obtaining Spectrometric Data for Object-Color Evaluation
Covers requirements for collecting accurate spectrometric data.
- ASTM E1767 – Practice for Specifying the Geometries of Observation and Measurement to Characterize the Appearance of Materials
Gives broader guidance on specifying measurement geometries beyond multiangle spectrophotometry.
Note: The standard specifically excludes retroreflective materials from its scope, as their unique properties are addressed in other ASTM documentation.
Summary
ASTM E2175-01(2021) ensures user confidence in multiangle spectrophotometer measurement results by providing a clear, unified framework for specifying instrument geometry and tolerances. Its adoption supports accurate, repeatable appearance measurements for gonioapparent materials, benefiting industries focused on high-quality surface finishing and color consistency.
Keywords: multiangle spectrophotometry, geometry specification, gonioapparent materials, metallic paint measurement, color quality control, appearance standards, ASTM E2175, spectrophotometer configuration, material appearance, color measurement standards.