ASTM D1729 specifies the equipment and procedures for the visual appraisal of colors and color differences of opaque materials that are diffusely illuminated, and these specifications are of critical importance in color matching. This practice uses the judgments of observers having at least normal color vision, and preferably better color vision, measured by the FM-100 Hue Test described in Guide E1499. The illumination required for critical visual appraisal of color and color difference of materials such as metallic and pearlescent paints is almost a geometric simulation of direct sunlight, as it provides the necessary illumination for the observation of sparkle and goniochromatism, which are outside the scope of this practice. The values in SI units are considered standard, and the values in parentheses are provided for information only.
The scope of ASTM D1729 includes:
- Material type: Opaque materials judged with diffused light for color and color difference.
- Purpose: To establish a uniform visual color appraisal system for color matching applications.
- Properties measured: Color and color difference between specimens.
- Method: Qualified observers make a visual comparison of the samples under the defined diffuse illumination and viewing conditions.
- Result: Judgment of color match, mismatch, or the perceived color difference.
- Test Limitations: Not applicable to metallic or pearlescent paints that require near-geometric simulation to observe sparkle and goniochromatism.
- Use conditions: Simulated average daylight (D65) is recommended, and D50 is recommended for color photography or color printing uses.
- Applications: Color-matching quality control in the paint, textile, plastic, and printed products industries.
What are the Uses of ASTM D1729?
ASTM D1729 evaluation provides a uniformly accepted method for visually evaluating color and color difference for opaque materials, while a quality control team analyzes the results to ensure color match before products are produced. This standard-
- Creates uniformity in the equipment and viewing conditions for visual color appraisal.
- Assists in color selection of paint, fabrics, plastics, and other translucent materials.
- Supports identification of metamerism to verify color matches under a second source of light.
- Helps in the qualification of observers for color judgment in the FM-100 Hue Test.
- Operates under three different illumination conditions: daylight (D65), photography, and printing (D50).
- Helps manufacturers ensure uniformity in products by visual inspection.
What Materials Are Covered and Tested Under ASTM D1729?
ASTM D1729 applies to opaque materials tested for color and color difference under diffuse illumination, such as paints, textiles, plastics, and other colored products across many sectors. The materials excluded from the practice are metallic and pearlescent paints, which show sparkle and goniochromatism and for whose correct observation a near-geometric simulation of direct sunlight is necessary. Laboratories take samples and compare them to standard color reference samples under the conditions of illumination specified.
Why is ASTM D1729 Important?
ASTM D1729 evaluation provides manufacturers the opportunity to use uniform illumination, viewing conditions, and observation standards, helping to ensure that the color decision is reliable and repeatable among different production lots. Color measuring instruments are very much in use, but color matching is generally done visually, and the standardization of visual examination has resulted in greater uniformity in products produced in a number of industries. The colors may look identical under one type of light source but not another, so confirming a match under a second source, very different than the first, helps identify metamerism before it is a problem in the field.
