The “AATCC EP1 Grayscale for Color Change” evaluation procedure, published by the American Association of Textile Chemists and Color Experts (AATCC), describes the use of the grayscale to visually assess color changes in textiles resulting from color fastness tests. For instrumental assessment of color change in a test sample, AATCC evaluation procedure 7 applies.
In principle, the result of a color fastness test is evaluated by visually comparing the difference in color or contrast between untreated and treated samples, using differences represented by a scale. The degree of color fastness is equivalent to the gray scale level at which the same color or contrast difference is considered to exist.
For the purposes of this procedure, the following terms apply:
When using the scale, the original textile piece and its corresponding exposed test sample are placed side-by-side in the same plane and in the same direction. Particular care is taken to create a sharp junction between the two material pieces. The gray scale is positioned along the edges of the test sample and the original textile sample, aligning the junction points of the textile and gray scale pair. To eliminate the influence of surrounding areas, the gray mask provided with the scale is placed over the samples and the scale. A white material with a tristimulus value of at least 85 is glued to the back of both the original and tested samples. If the samples are permanently mounted on a card, the card must have a tristimulus value of at least 85. Any fastening devices (such as staples) should not be visible in the area.
The surfaces are illuminated with a daylight simulator having an illumination level in the range of 1080-1340 lx at the sample plane. The light should strike the surfaces at an angle of 45 ± 5 degrees, and the viewing direction should be at an angle of 90 ± 5 degrees to the surface plane.
The perceived visual difference between the original and the tested textile is compared to the perceived differences represented by a grayscale. The color fastness rating is the number of the grayscale pair corresponding to the contrast between the original and the tested samples. Only 5 points are awarded when there is no perceptible difference in color or contrast between the original material and the tested sample. The cleanliness and physical condition of the grayscale are extremely important for obtaining consistent results.
After numerous evaluations, it is very useful to compare all pairs of original and tested samples that received the same numerical score. This provides a good indication of the consistency of the scores, as any errors become apparent. Pairs that do not appear to have the same degree of contrast with others having the same scores should be re-checked according to the gray scale, and the scores adjusted if necessary.
When using the grayscale, the character of the color change—whether lightness, hue, or chroma, or any combination thereof—is not graded; the overall difference or contrast between the original and tested samples forms the basis of the evaluation.
Color differences and tolerances between the reference gray and nine decimal places on the scale are expressed as the total color difference using the CIE 1976 L*a*b* color difference formula.
The equivalent of this evaluation procedure is the “ISO 105-A02 Textiles - Color fastness tests - Part A02: Grey scale for evaluating color change” standard published by the International Organization for Standardization (ISO). The AATCC EP1 procedure is technically the same scope as the ISO 105-A02 standard, but the procedures may differ in detail.
In short, the AATCC EP1 evaluation procedure helps evaluators assign a numerical score to the degree of color change in a tested fabric sample compared to its original state. This procedure is widely used worldwide in textile quality control. AATCC EP1 relies on human visual assessment under controlled lighting conditions. It focuses on overall color change but allows for noting components such as lightness, chroma, and tonal differences without quantification.
The grayscale consists of pairs of neutral gray chips representing progressively increasing differences in clarity:
Evaluators compare the tested sample to the scale under standard lighting (e.g., D65 daylight simulator) and assign the closest matching grade. Half-grades are used for intermediate differences.
Meanwhile, for comparison purposes, there is a separate dye stain grayscale (AATCC EP2) that evaluates color transfer to adjacent fabrics.
Colorfastness is critical for clothing, upholstery, and other textiles to ensure durability and consumer satisfaction. The AATCC EP1 is referenced in numerous AATCC test methods and helps manufacturers verify whether fabrics meet fading or color degradation performance standards.
Recent updates include improved durability features at the physical scale (e.g., edged designs to reduce scratching), and AATCC recommends annual replacement with periodic instrumental verification to maintain accuracy.
This visual tool remains a cornerstone of textile evaluation, combining subjective assessment with standardized, repeatable results.
For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services to businesses in accordance with the "AATCC EP1 Grayscale for Color Change" evaluation procedure.
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