Colour Fastness
Introduction:
Consumers don’t like their textiles to change colors or bleed during washing, under the sun or anywhere else. But how can anyone ensure textiles keep their color over time? Color fastness testing in a laboratory can help us to ensure fabric’s colors stay fresh and vibrant after many uses. Color fastness testing is essential to ensuring customer satisfaction with fabric products.
Colour Fastness:
Colorfastness is defined as the strength of the clothes against fading or running out of clothing colors. Another name for color fastness is dye fastness. It refers to the resistance of textile colors to effects such as color change or transfer during processing and use.
Types of Color Fastness in Textile and Apparel Sector:
1. Colorfastness to washing,
2. Colorfastness to heat,
3. Colorfastness to water,
4. Colorfastness to friction/rubbing,
5. Colorfastness to cold,
6. Colorfastness to burning.
Dependence Factors of Color Fastness:
Many factors affect the strength of colorfastness:
1. Chemical nature of clothing,
2. Molecule structure of dye (Dye Types),
3. Molecular state of dye,
4. Amount of dye.
5. Types of Fibre and compatible Dye
6. Type of conditions to which clothing is exposed
Some Terms Related to Colour Fastness:
Discoloration:
In printing and dyeing textiles under specific environmental factors, certain activities and reactions within the textile may result in color chroma, hue, and brightness changes. This effect is referred to as discoloration. Some of these occurrences within textiles include; when part of the dye is separated from the fiber, or the luminescent group of the dye is destroyed, or a new luminescent group is generated.
Staining:
Staining is a phenomenon where part of the dye on a piece of fabric is separated from its originally attached fiber and transferred to other lining fabrics when placed under various environmental factors, thereby staining the lining fabric.
Color changing gray card:
This contrast card comprises one standard scale of gray and a decreasing scale of gray chroma. The grayscale rating for the color change is determined using 5-grade levels and nine grades system with grade 5 representing the best Color Fastness and grade 1 representing the worst Color Fastness. The middle levels can be assessed as half grade such as grade 4-5, grade 4, and grade 3-4.
Stained gray card:
This comprises of a standard scale of white with a corresponding group of increasing gray chroma. There are five grades and nine grades system; grade 5 implies virtually no staining occurred. Hence great Color Fastness while grade 1 signifies the worst Color Fastness, and the middle can be assessed as half grade, such as grade 4-5, grade 4, and grade 3-4.
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Environmental requirements for Color Fastness ratings
Environment: darkroom:
The rating process should be done in a darkroom of constant humidity and constant room temperature. The color of the darkroom wall and the objects on the wall should be painted in neutral gray as well, which is similar to the rating gray card between level 1 and level 2 (approximately Monsell color Card N5). It is required that the entire darkroom must not have any other light sources except the light source of the rating lightbox. Also, ensure that no other sundries appear on the rating platform.
Light source and equipment:
The preferred general light source is the D65 light source. Its service life tube is 2000 hours. Customers can also specify other light sources, such as the F light source, 84-P light source, UV light source, etc.
Personnel requirements:
The grader should not be color-blind. They can be tested using a color-blindness detection chart or Farnsworth-Munsell 100 hue test kit.
Clothing requirements:
• Gray clothes are best.
• Avoid bright-colored clothes, bright-colored nail polish, and any items that may reflect the light source.
• Do not wear colored glasses.
• Do not rate when tired or sick. Rating is a subjective activity, and mood will affect the psychological, subjective judgment of color; for the same sample, when one is happy, it is one result and when they are down, it is another result.
• Observers must adapt to standard lighting conditions for at least 2 minutes before observation commences. This is to let the eyes adapt to the current light source environment.
• The raters require strict training and must pass the preset assessment.
Rating angle:
To use the gray card to rate the samples, you need to use the correct rating angle. The standard generally used entails that the sample and the horizontal plane be at 45° while the light source for rating and the sample are kept at 45°.
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How professional laboratories evaluate color fastness:
The American Association of Textile Chemists and Colorists (AATCC) and the International Organization for Standardization (ISO) color fastness standards are the most commonly used in the U.S.A and EU, respectively.
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