Mastering Color Fastness: Test Methods and Techniques for Exceptional Results

What is color fastness

In thie blog, we will explain: color fastness and test methods. Color fastness, also known as dye fastness or dye color fastness, refers to the resistance of textile colors to various influences during processing and use. It is assessed based on the color change of the sample and the staining of an undyed lining fabric.

Textiles are subjected to various external factors during their use, such as light exposure, washing, ironing, perspiration, friction, and exposure to chemicals. Some dyed textiles also undergo special finishing processes, such as resin finishing, flame-retardant finishing, sand washing, and brushing, which require the color to maintain a certain level of fastness.

Factors influencing color fastness:

Color fastness, also known as dye fastness, refers to the degree of color change that dyed fabrics undergo during use or processing under the influence of external factors such as squeezing, friction, washing, rain, exposure to sunlight, seawater immersion, saliva immersion, water stains, perspiration, etc. It is an important indicator of fabric quality and durability. The most common factors affecting color fastness include washing, light, rubbing, perspiration, ironing, and climate resistance.

When talk about color fastness and test methods, the choice of testing items depends on the final use and product standards. For example, woolen textile products must undergo testing for color fastness to sunlight, while knitted underwear requires testing for perspiration fastness. Outdoor textiles such as sunshades, lightbox fabrics, and canopy materials need to be tested for weather resistance color fastness.

How to Test Color Fastness in Textiles?

Washing Color Fastness:

Sew the test specimen together with a standard lining fabric and subject it to washing, rinsing, and drying under appropriate temperature, alkalinity, bleaching, and friction conditions to obtain test results in a short period. The friction is achieved through tumbling and impacting with a small bath ratio and an appropriate amount of stainless steel beads. The color fastness is evaluated using a gray scale card to determine the test results.

Different color fastness and test methods have specific temperature, alkalinity, bleaching, friction conditions, and sample sizes, which should be selected based on testing standards and customer requirements. Colors with generally poor washing color fastness include emerald, cyan blue, dark red, and navy blue, among others.

Dry Cleaning Color Fastness:

Similar to washing color fastness, but using dry cleaning instead of washing.

Rubbing Color Fastness:

Place the test specimen on a rubbing fastness tester and rub it a certain number of times with a standard rubbing white cloth under specific pressure. Perform both dry and wet rubbing color fastness tests. Evaluate the color transferred to the rubbing white cloth using a gray scale card to determine the rubbing color fastness. You must conduct both dry and wet rubbing tests, rubbing all colors on the specimen.

Light Color Fastness:

Textiles are often exposed to light during use, which can lead to color fading due to dye degradation. Generally, the colors may become lighter, darker, or undergo a change in hue. To test light color fastness, place the test specimen with blue wool standard fabric of different fastness levels under specified sunlight exposure conditions. Compare the test specimen with the blue wool fabric to assess lightfastness, where higher blue wool standard levels indicate better lightfastness.

Perspiration Color Fastness:

Sew the test specimen together with a standard lining fabric and subject it to perspiration treatment. Then, place it on a perspiration color fastness tester, followed by constant temperature drying in an oven. Evaluate the test results using a gray scale card. Different testing methods may have different perspiration liquid ratios, sample sizes, testing temperatures, and times.

perspiration colorfastness tester

Water Stain Color Fastness:

Conduct the same test as above using water treatment.

Chlorine Bleach Color Fastness:

Evaluate the degree of color change in the fabric after being washed in chlorine bleach solution under specific conditions. This determines the chlorine bleach color fastness.

Non-chlorine Bleach Color Fastness:

Evaluate the degree of color change in the fabric after being washed in a non-chlorine bleach detergent. This determines the non-chlorine bleach color fastness.

Ironing Color Fastness:

Cover the dry test specimen with cotton lining fabric and apply pressure with a heating device at a specified temperature and pressure for a certain period. Then, use a gray scale card to evaluate the color change of the test specimen and the staining on the lining fabric. Ironing color fastness includes dry ironing, damp ironing, and wet ironing tests, which should be chosen based on customer requirements and testing standards.

Types of Color Fastness Testing and Analysis:

Color fastness represents the degree of color variation in dyed textiles. It depends on various factors such as dye-fiber binding strength, yarn structure, fabric construction, dyeing methods, dye types, and external forces.

Common color fastness tests include lightfastness, weather fastness, wash fastness, rub fastness, and perspiration fastness, among others, which may have specific requirements for different textiles and usage environments.

During color fastness tests, evaluate color variation and staining on lining materials. Grade the results using a five-level scale, with the exception of lightfastness, which uses an eight-level scale. Higher levels indicate better color fastness.

Sunlight Fastness

Sunlight fastness refers to the degree of color change in colored fabrics when exposed to sunlight. The color fastness and test methods involves comparing the fading degree of the sample after simulating sunlight exposure with a standard color sample. It is graded on an 8-level scale, with level 8 being the best and level 1 being the worst. Fabrics with poor sunlight fastness should avoid prolonged exposure to direct sunlight and are better kept in well-ventilated areas for drying.

Washing Fastness

Washing fastness, also known as water or soap washing fastness, measures the degree of color change in dyed fabrics after you wash them with detergent. Typically, evaluate it based on the color difference between the original sample and the tested sample, using a grey scale as the standard. Grade washing fastness on a 5-level scale, with level 5 being the best and level 1 being the worst. Use fabrics with poor washing fastness more suitably for dry cleaning; if wet washing is necessary, pay special attention to washing conditions, such as avoiding high temperatures and prolonged washing times.

Rubbing Fastness

Rubbing fastness refers to the degree of color transfer in dyed fabrics after rubbing, both in dry and wet conditions. The evaluation is based on the extent of color transfer to a white cloth, using a 5-level scale, with higher values indicating better rubbing fastness.

Perspiration Fastness

Perspiration fastness is the degree of color change in dyed fabrics when exposed to perspiration.

Ironing Fastness

Ironing fastness refers to the degree of color change or fading in dyed fabrics during ironing.

Sublimation Fastness

Sublimation fastness measures the degree of sublimation (direct transition from solid to gas) of dyes in dyed fabrics during storage. Normally, fabrics are required to have a sublimation fastness of 3-4 levels to meet the requirements for wear.

Methods to Improve Color Fastness:

Factors affecting color fastness in textiles can be classified into internal and external factors. Internal factors refer to the firmness of dye-fiber binding, while external factors involve external forces or environmental conditions during product usage. Manufacturers should focus on enhancing the product’s inherent color fastness.

Proper Dye Selection:

Choosing the right dye is crucial for achieving good color fastness. Inappropriate dye selection, regardless of excellent auxiliaries and dyeing processes, can lead to low-quality color fastness. Select dyes suitable for specific fibers, considering dyeing performance and fastness.

1. Selecting Dyes Based on Fiber Characteristics.

Different types of dyes have varying affinities and bond strengths with different fibers. After determining the type of dye, dyes with high dyeing performance should be chosen. The color and bond strength of the dye may also vary depending on the specific dye used. For instance, weak acid dyes may provide higher color fastness for dyeing wool yarn compared to strong acid dyes. Pure cotton fabrics or regenerated cellulose fiber fabrics can be dyed using either direct dyes or reactive dyes, while silk fabrics can be dyed with weak acid dyes, certain reactive dyes, or some specific direct dyes.

2. Selecting Dyes Based on Color Depth.

Once you determine the general type of dye, base the specific dye to use on the color system and depth required for dyeing. Ideally, choose dyes with colors closest to the desired shade, and if there are deviations, use other dyes to adjust the color. Additionally, consider the inherent color fastness of the selected dye. You can improve dyes with lower inherent color fastness through appropriate processing. Also, evaluate the saturation of the dye to ensure it can achieve the desired color depth. Using dyes with very low exhaustion rates can result in temporary high color depth, but the dye may not be firmly bonded to the fiber and could be easily washed off or damaged during subsequent processing or daily use.

Each dye has a specified color fastness rating described in its product information. When selecting dyes, it is essential to choose dyes that meet the color fastness requirements of the product. Additionally, dyes with similar color fastness ratings should be selected for blending. If a dye’s inherent color fastness is low, even with the best auxiliaries and dyeing processes, it won’t be able to achieve a higher color fastness rating (e.g., 4-5) if the dye itself can only reach 2-3 or even 1-2. The color fastness of dyes primarily depends on the bonding strength between the dye and the fiber. If the bond is not strong, external forces such as washing or friction can disrupt the bond and result in color fading.

4. Dye Uptake Rate on Fibers.

Different dyes exhibit different uptake rates, which can vary under different dyeing conditions. Therefore, when selecting dyes, consider the dye uptake rate to avoid competitive dyeing phenomena. This can occur when one dye occupies the dyeing sites on the fiber, preventing other dyes from bonding uniformly to the fiber, leading to color discrepancies after dyeing. For optimal dyeing results, choose dyes with similar uptake rates under the same conditions.

5. Good Compatibility Between Dyes.

  • Dyes within the same class may have different compatibility values, with higher values indicating better blending ability.
  • Ensure good compatibility between dyes when blending.
  • For difficult-to-blend colors, use primary colors, which offer a complete range of combinations.
  • Use primary colors for challenging shades, avoiding other dyes to prevent competition and pattern issues.
  • Reduce the number of required dyes for simplified coloring and improved color purity, brightness, and saturation.
  • Minimize the number of required dyes: First, choose dyes close to the desired shade.
  • Use one or two additional dyes to supplement the primary dye.
  • Select dyes within the same color family for pure, smooth, vibrant colors.
  • Avoid using four or five dyes to achieve the desired shade as it may lead to color matching difficulties and challenges in handling large batches.
  • Even if the color matches, it may lack brilliance and fullness due to poor dye-fiber bonding, resulting in weak color fastness.
Color fastness tester to washing

Selection and use of auxiliaries for textile dyeing:

1. Choose suitable auxiliaries:

After determining the type of dye, the selection of appropriate auxiliaries is crucial. Use auxiliaries compatible with the chosen dye whenever possible. When dealing with regular conventional dyes, pay particular attention to determining the appropriate auxiliary dosage and usage method. If you’re dealing with deep colors where dyes do not easily exhaust, add auxiliaries in separate batches to enhance exhaustion rates and improve the dye’s adhesion to the fibers, which ensures better color fixation.

2. Minimize the use of leveling agents:

When using leveling agents with retarding effects, it is essential to minimize their dosage to avoid stripping the dye. Excessive leveling agents can reduce the exhaustion rate and weaken the bond between the dye and the fiber, leading to reduced color fastness. For colors prone to uneven dyeing, achieving uniform dyeing can be achieved through dye blending and temperature adjustments.

3. Selection of fixing agents:

Using fixing agents can significantly improve the color fastness of the dye. Generally, they can enhance the color fastness by at least 0.5 to 1 level. However, when choosing fixing agents, it is crucial to consider various aspects of dye fastness, not just individual factors. For instance, when using cationic low-molecular-weight or polyamine fixing agents for reactive dyes, the washing fastness of the fabric may be enhanced to level 4-5, but the light fastness may be slightly compromised. Therefore, it is essential to strictly control the dosage, temperature, and time of the fixing process.

4. Soaping and washing:

During the soaping and washing processes, it is crucial to ensure thorough washing and to maintain appropriate water temperature and time. Inadequate washing can result in color bleeding during product use.

5. Use of softeners:

To achieve a full and soft hand feel for the product, softeners should be added during the finishing process. Softeners can be cationic, anionic, nonionic, or organic silicon-based. Softeners are applied after the dyeing process, where further reactions may occur between the dye and the softener. It is essential to note that the use of organic silicon-based softeners can cause color fading. Especially after dyeing with acid dyes, this may result in a slightly lighter color shade. Therefore, carefully adjust the dosage of softeners during the softening process. Avoid not only stickiness but also any negative impact on the dyeing results.

In summary, improving color fastness in textiles requires attention to dye selection, proper use of auxiliaries, appropriate fixing agent usage, careful washing and rubbing techniques, and cautious softener application. By addressing both internal and external factors, textile manufacturers can enhance color fastness and produce products that meet customer expectations for durability and color retention and product longevity.

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