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D4086-18 – Standard Test Method Technical Guide
📐 Scope and Terminology Overview
This standard practice covers visual methods for detecting metamerism and estimating the magnitude of metameric color differences. It specifically addresses illuminant metamerism and observer metamerism, as defined in Section 1.2. The term “metamerism” refers to the property where two specimens match under one set of illuminating and viewing conditions but differ in spectral characteristics, leading to a mismatch under different conditions (Section 3.2.1). As noted in the introduction, metamerism is often described as “invisible spectral differences.”
| 🟦 Term | 📏 Definition | 🎯 Source |
|---|---|---|
| Metamerism | Property of two specimens that match under a specified illuminator and to a specified observer and whose spectral reflectances or transmittances differ in the visible wavelengths. | Section 3.2.1 |
| Paramerism | Phenomenon in which specimens having different spectrophotometric curves produce approximately the same color sensation under the same illuminating and viewing conditions. | Section 3.2.2 |
⚙️ Visual Evaluation Procedure
The practice outlines visual methods for assessing metamerism, utilizing Test Method D2616 for evaluating color differences with a gray scale. It is important to note that this practice does not cover gonioapparent samples (Section 1.2) nor does it provide for computation of metamerism indices from instrumental data (Section 1.3). The evaluation requires careful control of illuminating and viewing conditions to detect matches or mismatches, and the direction and magnitude of color difference may change under different conditions.
⚠️ This practice is limited to illuminant and observer metamerism. Gonioapparent samples and instrumental computations are explicitly excluded.
📊 Key Referenced Standards
The standard references several ASTM documents for additional guidance. Test Method D2616 provides the gray scale method for evaluating visual color differences, while Terminology E284 supplies definitions for appearance terms including those used in this practice.
| 🟦 Type | 📏 Description | 🎯 Reference |
|---|---|---|
| Illuminant Metamerism | Mismatch due to differences in light source spectral power distribution | Section 1.2 |
| Observer Metamerism | Mismatch due to variations in observer color vision | Section 1.2 |
❓ Frequently Asked Questions
🔍 What is metamerism?
Metamerism is the property where two specimens match under one set of illuminating and viewing conditions but not under another, due to differences in spectral characteristics.
💡 How is metamerism evaluated in this practice?
This practice uses visual methods, including the gray scale from Test Method D2616, to estimate the magnitude of metameric color differences.
⚡ What types of metamerism are covered?
The practice covers illuminant metamerism and observer metamerism, but does not cover gonioapparent samples.
📌 What standards are referenced?
Referenced standards include D2616 for visual color difference evaluation and E284 for terminology of appearance.