Color fastness is a key indicator that measures a textile’s ability to resist external factors and retain its original color during processing and use. For textile companies, color fastness not only directly affects product appearance and the consumer experience but is also a core testing requirement in export trade and brand certification.

I. Wash Fastness

1.1 Testing Principles and Standard Basis

The core concept of wash fastness testing is as follows: After sewing the test specimen to a standard backing fabric (such as cotton, polyester, or wool), it is subjected to simulated washing in a washing solution at a specific temperature and for a specific duration using a designated detergent formulation. Subsequently, the degree of color change in the test specimen and the degree of color transfer to the backing fabric are evaluated. Rating is based on the gray scale comparison method, with Grade 1 being the poorest and Grade 5 the best.

In China, the primary standard is GB/T 3921-2008 “Textiles—Color Fastness Tests—Color Fastness to Soap Washing,” while internationally, the ISO 105 C series and AATCC 61 standards are widely adopted. Different standards vary in terms of washing temperature, duration, and detergent formulations. For example, GB/T 3921 specifies multiple temperature levels ranging from 40°C to 95°C, while AATCC 61 employs an accelerated washing method that simulates multiple home washes by shortening the duration and increasing the temperature.

1.2 Key Considerations for Equipment Selection

Temperature Control Accuracy and Uniformity: Washing temperature is the primary variable affecting test results. High-quality equipment should maintain temperature control accuracy within ±1°C, with a temperature difference of no more than 2°C at any point within the drum. Some budget-friendly models use water bath heating, which suffers from significant temperature fluctuations and uneven heating across different test specimens. This is particularly prone to causing data deviations for samples with high heat capacity, such as down jackets and heavy fabrics.

Drum Rotation Speed and Mechanical Action: Standards specify the drum rotation speed (typically 40±2 r/min); deviations in speed directly affect the degree of dye migration. When selecting equipment, verify the stability of the motor drive system and prioritize models with variable-frequency speed control and closed-loop control.

Sample Capacity and Fixture Design: Select the number of drums based on daily testing throughput; common configurations include 6, 8, or 12 cups. Fixtures should allow for quick loading and unloading while ensuring that samples do not become tangled or shift during the washing process. For printed fabrics, ensure that the samples cover all color areas; increase the number of samples if necessary.

1.3 Key Quality Control Points

The selection of interlining must strictly adhere to the standard—pure-fiber specimens should use interlining made of the same fiber, while blended-fiber specimens should be matched separately according to the major and minor fibers. The pH of the washing solution, detergent concentration, and bath ratio (volume ratio of specimens to washing solution) must all be precisely controlled. In addition, the conditioning of specimens prior to testing (equilibration under standard atmospheric conditions for at least 4 hours) directly affects the consistency of the final rating.

II. Rub Fastness

2.1 Differences Between Dry and Wet Rubbing

Colorfastness to rubbing evaluates a textile’s ability to resist color transfer when subjected to repeated rubbing on a dry or damp surface. It is divided into two test conditions: dry rubbing and wet rubbing. Dry rubbing simulates the friction between garments and between garments and skin during everyday wear; wet rubbing simulates friction in sweaty or damp environments and is particularly critical for dark denim and reactive-dyed cotton fabrics.

During testing, a standard white cotton rub sheet is secured to the rubbing head and rubbed back and forth across the surface of the test specimen 10 times at a specified pressure (typically 9 N) and stroke length (104 ± 3 mm). The degree of color transfer to the rub sheet is then evaluated using a gray scale.

2.2 Key Considerations for Equipment Selection

Stability of Pressure and Stroke: The pressure applied by the rubbing head to the test specimen must be constant, and stroke consistency directly affects the repeatability of results. Electric models offer better speed control than hand-cranked models; it is recommended to select an electric colorfastness to rubbing tester equipped with an electronic counter that allows presetting the number of rubs and automatically stops the test. Dual-station models can significantly improve testing efficiency and are suitable for daily quality control in mass production.

Rubbing Head Material and Surface Treatment: Standard rubbing heads are typically cylindrical steel pins with a diameter of 16 mm; their surfaces should be smooth and free of burrs. Certain special materials (such as leather and coated fabrics) may require the use of round friction heads or other specialized fixtures.

Water Control Capability for Wet Rubbing: Wet rubbing tests require the uniform application of a specified amount of water to the friction cloth (typically at a moisture content of 95%–100%). The equipment should be equipped with a precise, metered water dispensing device or clear operating instructions to prevent result fluctuations caused by uneven water distribution.

2.3 Key Quality Control Points

The wet rub colorfastness of dark-colored fabrics (especially black, navy blue, and bright red) is often a major source of customer complaints. Special attention must be paid during testing: The rubbing cloth must be a cotton fabric that has undergone desizing, bleaching, and mercerization in accordance with the standard; the surface of the test specimen should be flat and free of wrinkles, and for printed areas, ensure that all colors are subjected to rubbing; grading should be conducted under a standard light source (such as D65) to avoid visual deviations caused by the color temperature of ambient light.

Ⅲ. Rub Fastness

3.1 Differences Between Dry and Wet Rubbing

Colorfastness to rubbing evaluates a textile’s ability to resist color transfer when subjected to repeated rubbing on a dry or damp surface. It is divided into two test conditions: dry rubbing and wet rubbing. Dry rubbing simulates the friction between garments and between garments and skin during everyday wear; wet rubbing simulates friction in sweaty or damp environments and is particularly critical for dark denim and reactive-dyed cotton fabrics.

During testing, a standard white cotton rub sheet is secured to the rubbing head and rubbed back and forth across the surface of the test specimen 10 times at a specified pressure (typically 9 N) and stroke length (104 ± 3 mm). The degree of color transfer to the rub sheet is then evaluated using a gray scale.

3.2 Key Considerations for Equipment Selection

Stability of Pressure and Stroke: The pressure applied by the rubbing head to the test specimen must be constant, and stroke consistency directly affects the repeatability of results. Electric models offer better speed control than hand-cranked models; it is recommended to select an electric colorfastness to rubbing tester equipped with an electronic counter that allows presetting the number of rubs and automatically stops the test. Dual-station models can significantly improve testing efficiency and are suitable for daily quality control in mass production.

Rubbing Head Material and Surface Treatment: Standard rubbing heads are typically cylindrical steel pins with a diameter of 16 mm; their surfaces should be smooth and free of burrs. Certain special materials (such as leather and coated fabrics) may require the use of round friction heads or other specialized fixtures.

Water Control Capability for Wet Rubbing: Wet rubbing tests require the uniform application of a specified amount of water to the friction cloth (typically at a moisture content of 95%–100%). The equipment should be equipped with a precise, metered water dispensing device or clear operating instructions to prevent result fluctuations caused by uneven water distribution.

3.3 Key Quality Control Points

The wet rub colorfastness of dark-colored fabrics (especially black, navy blue, and bright red) is often a major source of customer complaints. Special attention must be paid during testing: The rubbing cloth must be a cotton fabric that has undergone desizing, bleaching, and mercerization in accordance with the standard; the surface of the test specimen should be flat and free of wrinkles, and for printed areas, ensure that all colors are subjected to rubbing; grading should be conducted under a standard light source (such as D65) to avoid visual deviations caused by the color temperature of ambient light.

Ⅳ. Lightfastness

4.1 Test Principle and Selection of Light Sources

Lightfastness testing simulates the color stability of textiles when exposed to sunlight and is a mandatory test item for products such as curtains, outdoor apparel, and automotive interiors that are subject to long-term exposure to light. The testing principle involves simultaneously exposing the test specimen to an artificial light source alongside a set of blue wool standards with known lightfastness ratings (18 levels, where Level 1 indicates the poorest lightfastness and Level 8 the best). The rating is determined by comparing the color changes in the test specimen with those of the blue wool standards.

The choice of light source is the key differentiator among lightfastness testing instruments. Currently, there are three mainstream options:

Xenon Arc Lamp: Its spectral energy distribution most closely resembles natural sunlight, covering the ultraviolet, visible, and infrared bands. It is currently the internationally recognized preferred light source, corresponding to standards such as ISO 105 B02, AATCC 16, and GB/T 8427.

Carbon Arc Lamp: Historically the first light source used for textile lightfastness testing, but its spectrum differs significantly from natural sunlight. The energy distribution in the short-wave ultraviolet and visible light regions does not match that of natural sunlight, resulting in poor correlation between test results and actual weather resistance. It is now gradually being phased out.

Mercury Vapor Lamps: Their spectral lines are primarily concentrated in the ultraviolet region (around 365 nm) and are mostly used for durability testing of outdoor products; they are rarely applied in the field of textile colorfastness.

4.2 Key Considerations for Equipment Selection

Light Source Cooling Methods: Xenon arc lamps are divided into two types: air-cooled and water-cooled. Air-cooled models have a relatively simple structure and low maintenance costs, making them suitable for laboratories with modest testing volumes; Water-cooled models use high-power xenon lamps and offer a large test area, but they require a high-purity cooling water circulation system, resulting in significantly higher acquisition and maintenance costs. For most textile company laboratories, air-cooled flat-panel xenon lamp testers are sufficient to meet daily needs.

Irradiance Control System: Irradiance directly determines the rate of dye photodegradation and is the key variable affecting the stability of test results. High-quality equipment should support irradiance settings of 1.1 W/m² at 420 nm or 42 W/m² in the 300–400 nm wavelength band, and feature closed-loop automatic adjustment. Be wary of some budget-friendly models that offer only “power adjustment” rather than “irradiance control”; as the xenon lamp ages and its output power decreases, the actual irradiance will drift, severely affecting data comparability.

Coordinated Temperature and Humidity Control: The combined effect of light and high temperature accelerates the degradation of textiles; therefore, precise control of Black Panel Temperature (BPT) or Black Standard Temperature (BST) and relative humidity is critical. Both ISO and AATCC standards impose strict requirements in this regard, and the equipment should be equipped with independent temperature and humidity sensors and control systems.

Calibration System: The irradiance of xenon lamps may decay by 5% to 15% over their service life, so a regular calibration mechanism must be established. Common calibration methods include the standard lamp method, the irradiance meter method, the standard blue wool method, and the spectrometer method. Among these, the irradiance meter method and the standard blue wool method are adopted by most laboratories due to their ease of operation and moderate cost.

4.3 Key Quality Control Points

Lightfastness testing typically involves long durations (ranging from several hours to hundreds of hours), and any loss of control over conditions can result in significant losses. Daily quality control should focus on the following: the aging status of the xenon lamp and filters, ensuring timely replacement; the position and surface condition of the black panel temperature sensor to ensure it is in the same thermal environment as the test specimens; the mounting method of the test specimens to avoid edge effects; and the storage conditions of the blue wool standard to prevent changes in its own lightfastness rating.

Conclusion

Colorfastness testing is the cornerstone of textile quality control. The three key tests—washfastness, rubfastness, and lightfastness—cover the most common scenarios of color fading encountered by consumers during daily use. Selecting the right equipment provides laboratories with a reliable data foundation, while a rigorous quality control system is the fundamental guarantee of data accuracy and comparability. In today’s increasingly competitive textile industry, an accurate, efficient, and compliant color fastness testing solution is not only a prerequisite for meeting customer factory audit and export certification requirements but also a vital pillar for companies to enhance product value and build brand credibility.

If you have any questions regarding the selection of color fastness testing equipment or laboratory setup, please feel free to contact the UTSTESTER technical team. We will provide you with professional consultation and customized solutions.

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