Testing fabric color fastness with gray cards is a fundamental and crucial evaluation method in the textile industry. It primarily serves to objectively assess the degree of color change in textiles after undergoing tests such as rubbing, washing, perspiration exposure, and light exposure, as well as the potential for color transfer to adjacent fabrics.

1. What is Fabric Color Fastness?

Colored fabrics during production or garments made from them during use are subjected to various external environmental factors. The ability to resist these external forces is termed the colorfastness property of the fabric or garment.

2. What is Fabric Discoloration?

In dyed textiles, environmental factors can cause fiber color loss, destruction of dye chromophores, or generation of new chromophores. This leads to changes in color saturation, hue, and brightness.

3. What is fabric color migration?

This refers to the phenomenon where, under various environmental influences, dyes detach from the originally coated fibers and transfer to other fabrics, causing them to become stained.

During colorfastness gray scale grading, discoloration and migration gray scales are used to evaluate colorfastness. Currently used gray scales include AATCC, ISO, JIS, and Chinese National Standard GB gray scales. Each gray scale has slightly different gray levels.

4.How to Use Gray Scales to Test Fabric Color Fastness

4.1 Discoloration Gray Scale: Used to evaluate changes in the test sample's own color. It consists of 5 pairs of small gray cards, ranging from Level 5 to Level 1.

Level 5 indicates no change at all, while Level 1 indicates the most severe change. Within each pair, the left card is a fixed neutral gray, and the right card gradually lightens in shade, representing the degree of color change.

4.2 Dye Transfer Gray Cards: Used to evaluate the degree of color transfer from the test sample to an adjacent white fabric (commonly called the backing fabric). Consists of 5 pairs of small white and gray cards, ranging from Level 5 to Level 1.

Level 5 indicates no color transfer whatsoever, while Level 1 indicates the most severe color transfer. In each pair, the left card is a fixed white, and the right card is a progressively darker gray, representing the degree of color transfer.

5. Color Fastness Gray Scale Evaluation Method

Grading Scale Table

Masking Card

(As shown above), during grading, specially designed apertures are used to mask sample cards for evaluating multi-fiber fabric staining, rubbing colorfastness staining, and general staining assessment.

Using masking cards allows better focus on the sample being graded while covering other areas to prevent visual interference.

6. Grading Environment

6.1 Light Source

We commonly use the D65 light source. The bulb lifespan is 2000 hours. Other light sources may be specified, such as F light source, 84-P light source, UV light source, etc.

6.2 Darkroom Lighting

Darkroom: The grading process must be conducted in a darkroom with constant humidity and temperature. Additionally, the walls and furnishings of the darkroom must be painted in a neutral gray shade, approximately matching the level between Grade 1 and Grade 2 on the gray scale (roughly equivalent to Munsell N5). As shown in the image above, the left side displays the neutral gray of the walls with the lights on, while the right side shows the color after the lights are turned off. The entire darkroom must be free of any light sources other than the light source from the grading lightbox. Furthermore, no other objects should be present on the grading table.

7. Observer's Line of Sight

Grading Angle

Grading samples using gray cards requires precise angles! This standard mandates:

- Sample positioned at 45° to the horizontal plane

- Grading light source at 45° to the sample

- Observer's eyes at 90° to the sample

Observer-to-sample distance: 50-70 cm.

8. Precautions for Viewing Color Fastness Evaluation Cabinets

8.1 Light Source is Critical: Grading must never be conducted under everyday indoor lighting (e.g., incandescent or fluorescent lamps), as results will be severely distorted.

8.2 Viewing Angle: During observation, the sample and gray card should be placed on the same plane, with the line of sight forming approximately a 45° angle to the sample surface.

8.3 Multiple-Rater Grading: For greater objectivity, two or more graders should independently evaluate samples, then average the ratings. If discrepancies exceed 0.5 grades, a third grader must re-evaluate or consensus must be reached through discussion.

Gray Scale Maintenance: Gray scales are precision instruments. Avoid soiling, scratching, and light exposure. Store in protective sleeves after use.

Gray scale grading represents the final presentation of colorfastness test results and constitutes the concluding step in colorfastness testing. Regardless of prior process accuracy and standardization, grading errors can invalidate the entire test. Grading remains a challenging task. Ensuring consistency among personnel within the same laboratory is crucial, as is maintaining consistency between testing institutions. As more brands collaborate with multiple laboratories, inter-laboratory consistency becomes increasingly vital.

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