Color Fastness Standards & Grey Scale Rating

In our daily lives, the color of clothing plays a significant role. However, as garments are worn and washed repeatedly, fabric colors often fade gradually. This is where color fastness becomes crucial. So, what exactly is color fastness? What are the common standards for color fastness ratings?

Color fastness ratings primarily utilize grey scale cards, with variations including:

• AATCC (American) Standard Grey Scale
• ISO (International) Standard Grey Scale
• JIS (Japanese) Standard Grey Scale
• GB (Chinese) Standard Grey Scale

Each grey scale card consists of 5 grades and 9 steps, denoted as 1, 2, 3, 4, and 5, where 5 is the highest grade and 1 is the lowest. Intermediate half-grades can also be assessed. Notably, AATCC employs a decimal notation (e.g., 3.0, 3.5), while ISO, JIS, and GB use a hyphenated format (e.g., 3, 3-4).

Color Fastness refers to the degree to which a fabric resists color fading during usage and washing. Ratings are typically determined through standardized testing methods. Common color fastness rating standards include:

1. American Standard (AATCC): Developed by the American Association of Textile Chemists and Colorists, AATCC ratings range from 1 to 5, with 1 indicating poor fastness and 5 indicating excellent fastness.

2. European Standard (ISO): Established by the International Organization for Standardization, ISO ratings also range from 1 to 5, following the same scale as AATCC.

3. Japanese Standard (JIS): Formulated by the Japanese Industrial Standards Committee, JIS ratings range from 1 to 5, aligned with the international scale.

4. Chinese Standard (GB): Based on China’s national standards, GB ratings similarly range from 1 to 5.

Different fabrics adhere to distinct color fastness standards. For instance, cotton, linen, silk, and wool typically follow AATCC and ISO guidelines, whereas polyester and nylon often conform to JIS standards.

Understanding color fastness ratings is vital as they impact both the aesthetic longevity and quality of fabrics. When purchasing clothing, considering color fastness ratings can help select more durable and high-quality garments.

What is Color Fastness?
Color fastness, also known as dye fastness or colorfastness, refers to a textile’s resistance to color fading or transfer when subjected to various external factors during processing or usage. Ratings are assessed based on color change in the sample and staining on adjacent fabrics. Color fastness testing is a routine quality check for textiles, as fabrics are exposed to light, washing, ironing, perspiration, friction, chemicals, and other agents. Special finishes like resin treatments or flame retardants further necessitate color stability.

Key Testing Methods and Ratings:

1. Color Fastness to Rubbing:
   • For wet rubbing tests, excess fibers are removed from the cotton cloth after drying. Three layers of cotton are placed behind each tested cloth, and staining is evaluated using a grey scale for staining.
2. Color Fastness to Soaping, Water, Perspiration, Saliva, and Seawater:
   • Ratings are based on comparisons between tested samples, original samples, and untreated adjacent fabrics, assessing both color change and staining.
3. Staining of Wash Liquor:
   • Post-soaping (per FZ/T 73020-2019), the liquor is evaluated within 15 minutes. After impurity removal, it is compared to an unwashed reference using a grey scale for staining under D65 lighting with a white backdrop.
4. Light Fastness:
   • Following GB/T 8427-2019 Method 3, samples are exposed alongside blue wool references until fading occurs. Ratings are determined by comparing sample fading to the blue wool standards. If results vary across stages, an arithmetic mean is used, rounded up to the nearest half or whole grade (AATCC uses a grey scale for post-exposure comparisons).
5. Composite Light and Perspiration Fastness:
   • Per GB/T 14576-2009, samples are exposed with blue wool references, then washed, dried, and rated for color change using a grey scale.
6. Thermal Pressing Fastness:
   • Immediate color change rating is conducted post-testing, followed by a reassessment after 4 hours of standard conditioning, focusing on heavier staining on cotton adjacents.
7. Crocking Fastness in Composite Fabrics:
   • After washing and drying, light-colored fabrics are rated for staining using a grey scale.
8. Dry Cleaning Fastness:
   • New (GB/T 5711-2015) and old (GB/T 5711-1997) standards exist. The old method uses solvent filtration and transmission light for staining assessment, while the new method compares samples to references for color change and staining.
9. Phenolic Yellowing Resistance:
   • Post-testing, samples are cooled and rated within 30 minutes. Control fabric yellowing is assessed first (≥3 grade for validity), followed by sample yellowing using a grey scale. Testing methods vary by yellowing cause:
     • Light-Induced: GB/T 8427-2008 (xenon arc) and GB/T 30669-2014 (UV).
     • Phenolic: GB/T 29778-2013, SN/T 2468-2010 (BHT exposure).
     • Chlorine Bleach-Induced: FZ/T 01078-2009 (chlorine exposure and comparison).
10. Color Fastness to Chlorinated Water, Ozone, and Hypochlorite Bleach:
    • Ratings are based on color change comparisons using a grey scale.

Rating Methodologies:

• Color Change Rating: Post-test samples vs. originals using a grey scale.
• Staining Rating: Post-test light samples/adjacents/liquor vs. references using a grey scale.
• Light Fastness Rating: Sample fading vs. blue wool standards (GB) or originals (AATCC).

Consistent rating accuracy is critical, requiring intra- and inter-laboratory comparisons to maintain reliability.