Keeping Colors True: The Science of Textile Color Fastness Testing

Color fastness, also known as dye fastness, refers to the ability of dyed fabrics to maintain their original color when subjected to various external factors during use or processing. These factors include pressure, friction, washing, rain, exposure to sunlight, perspiration, ironing, and dry cleaning. The level of color fastness directly determines the fabric’s appearance stability and durability during use.

The importance of color fastness is mainly reflected in the following three aspects:

• Impact on the quality of textiles:

Color fastness is one of the key indicators for evaluating dyeing quality. Fabrics with poor color fastness tend to fade or discolor during use, which not only affects their aesthetic appearance but also lowers product quality, leading to consumer complaints and damage to brand reputation.

• Impact on staining of other materials:

When dyed fabrics come into contact with other textiles or materials, poor color fastness may cause dyes to migrate or transfer, resulting in staining of adjacent items. For example, dark-colored garments may bleed during washing or wearing, contaminating light-colored clothing and affecting overall usability.

• Impact on human health and safety:

When dyes are not firmly fixed to fabrics, they may be absorbed by the human body through skin contact or perspiration. Some dye decomposition products (such as aromatic amines) may pose allergenic or potential carcinogenic risks. Therefore, color fastness is not only a matter of quality but also an important health and safety indicator.
In summary, testing and controlling color fastness is essential for ensuring textile quality, protecting consumer safety, and promoting fair international trade.

General Rules for Color Fastness Testing

Color fastness testing simulates the external conditions that fabrics experience during actual use under standardized test methods, in order to evaluate the degree of color change and staining. Test results are typically expressed in gray scale ratings.
To ensure scientific accuracy and consistency, national standards provide detailed specifications for the types of adjacent fabrics, their combinations, sample preparation, and test solutions.

Types of Adjacent Fabrics
In color fastness testing, adjacent fabrics are auxiliary materials used to assess whether dyes from the test specimen will transfer to other materials. According to their composition and use, adjacent fabrics are divided into two types: single-fiber adjacent fabrics and multifiber adjacent fabrics.
Single-Fiber Adjacent Fabrics
According to standards GB/T 7568.1–7568.6-2002 Textiles — Tests for Colour Fastness — Specification for Standard Adjacent Fabrics — Parts 1–6,
six types of single-fiber adjacent fabrics are specified: Wool fiber (FZ/T 01057.1),Cotton and viscose fiber, Polyamide fiber, Polyester fiber, Polyacrylonitrile fiber, Silk fiber.
Single-fiber adjacent fabrics are generally used in specific tests for single-component or blended textiles.
Multifiber Adjacent Fabrics
According to GB/T 7568.7-2008 Textiles — Tests for Colour Fastness — Standard Adjacent Fabrics — Part 7: Multifiber, the multifiber adjacent fabric is a plain-woven fabric composed of several commonly used fibers—typically cotton, wool, polyester, nylon, acrylic, and acetate fibers. This type of adjacent fabric allows simultaneous evaluation of dye staining on different fiber materials in a single test, offering high efficiency and convenience, and is widely used in routine color fastness testing.

Dimensions and Use of Adjacent Fabrics​
When Using Two Pieces of Single-Fiber Adjacent Fabrics

• When single-fiber adjacent fabrics are used, two pieces are typically required: The first piece should be made of the same fiber type as the test specimen. The second piece should be selected according to the test method or the fiber composition of the specimen. If the specimen is a blended or interwoven fabric, the first adjacent fabric should correspond to the main component fiber, and the second to the secondary component fiber. The dimensions of the adjacent fabrics should be the same as the specimen, generally 40 mm × 100 mm.
• When Using One Piece of Multifiber Adjacent Fabric. When a multifiber adjacent fabric is used, it should cover only the face side of the specimen. The dimensions are also 40 mm × 100 mm.

Preparation of Composite Specimens
The method of assembling composite specimens varies depending on the type of test sample:
1.Ordinary Fabrics
Place the face side of the specimen in contact with one piece of multifiber adjacent fabric, or sandwich it between two pieces of single-fiber adjacent fabrics. Sew along the short edge to form a composite specimen.
2.Printed Fabrics
Ensure that all colors and patterns of the printed specimen are fully in contact with the adjacent fabric. Common methods include:
Placing the face side of the specimen in contact with half of each of two single-fiber adjacent fabrics, with the other halves overlapping the back side; or
Placing the face side in contact with one piece of multifiber adjacent fabric and sewing them together.
If a single composite cannot cover all printed colors, prepare multiple composite specimens.
3.Double-Sided Fabrics
For double-sided fabrics with different primary fibers on each side, ensure that each side is in contact with the corresponding single-fiber adjacent fabric. If necessary, prepare twocomposite specimens, each paired with a multifiber adjacent fabric.
4.Yarns or Loose Fibers
Take a sample weighing approximately half the total mass of two pieces of single-fiber adjacent fabrics, and place it between two single-fiber adjacent fabrics;
or take a sample weighing approximately equal to one piece of multifiber adjacent fabric, sandwich it between a multifiber adjacent fabric and an undyed fabric (such as polypropylene cloth), sew along all four edges, and add additional stitching at 10 mm intervals.

Conditioning Requirements
In general, the specimen and adjacent fabrics do not require special conditioning before testing. However, if differences in moisture content may affect the test results, conditioning must be carried out in accordance with GB/T 6529-2008 Textiles — Standard atmospheres for conditioning and testing.
The standard atmospheric conditions are: Temperature: 20 ± 2 °C, Relative humidity: 65 ± 4 %
The purpose of conditioning is to allow the fibers to reach moisture equilibrium before testing, ensuring the accuracy and comparability of test data.

Test Solution Requirements
The test solution used in color fastness testing must comply with the quality standards for laboratory-grade water, to prevent impurities from affecting the test results.
Water Quality
The solution should be prepared using Grade 3 distilled water, as specified in GB/T 6682 Water for analytical laboratory use — Specification and test methods (ISO 3696).
Definition of Liquor Ratio
The liquor ratio refers to the ratio of the volume of the test solution to the mass of the specimen or composite specimen (including the adjacent fabrics). Volume is expressed in milliliters (mL). Mass is expressed in grams (g).
A proper liquor ratio directly affects dye dissolution, migration, and interaction, and therefore must be strictly controlled according to the requirements of the specific test method.

More details can be found here.