1.Color fastness definition: What is color fastness?

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. The fastness grade, i.e., the degree of color fastness of fabric, is evaluated according to the discoloration of a sample and the staining of the undyed lining fabric.

During use, textiles are usually exposed to external factors such as light, washing, ironing, sweat, friction, and chemical agents. Some printed and dyed textiles are also subjected to special finishing processes, such as resin finishing, flame retardant finishing, sand-washing, and grinding. This demands that the color of printed and dyed textiles relatively maintain a specific fastness, i.e. good color fastness tester performance.

2. Harm of poor color fastness of textiles

The danger of a textile’s poor color fastness is quite eminent. When textile products with poor color fastness are exposed to water, sweat, sunlight or physical friction, the dyes may eventually fall off or fade. Thus, the appearance of the textile product is negatively affected. During use, the shed dye molecules or heavy metal ions may be absorbed by the human body through the skin, thereby endangering the user’s health, in short, poor color fastness is unacceptable.

3. Classification of color fastness, what are the different categories of color fastness?

In actual work, it is the end-use of a product and product standards that determine the test elements or conditions used. For example, the wool textile product standard stipulates that producers must test the wool’s color fastness to sunlight. Of course, the sweat color fastness of knitted underwear must be tested, while outdoor textiles (Such as parasols, light box cloth, canopy materials) must undergo a color fastness to ozone test test to weather resistance.

There are six common color fastness classifications:

3.1. Color fastness to rubbing

Rubbing fastness refers to the degree of color fading of dyed fabrics after rubbing. This can either be from dry rubbing or wet rubbing. The rubbing fastness is determined from the degree of a prespecified white cloth’s staining, and it is graded in 5 levels. The larger the value, the better the rubbing fastness.

3.2. Lightfastness

Lightfastness refers to the degree of discoloration of colored fabrics when exposed to sunlight. The Color Fastness to light test is done by comparing the degree of fade of the sample after simulating sunlight with a standard color sample divided into eight grades; 8, as the resulting value, implies the best while 1 implies the worst lightfastness. In essence, for fabrics to remain in optimal condition, they should not be exposed to sunlight for long periods, and they should also always be dried under shade, in a ventilated area.

3.3. Color Fastness to sublimation

This is the degree of sublimation dyed fabrics undergo in storage. The dye fastness of normal fabrics generally requires 3-4 grades in this category to meet wearing needs.

3.4. Washing Color Fastness

Washing or soaping fastness refers to the degree of the color change of dyed fabric after washing with a washing liquid. Usually, a gray graded sample card is used as the evaluation standard; that is, the color difference between the original sample and the faded sample is used for judgment.

Washing fastness is graded into five levels; grade 5 is the best while grade 1 is the worst level of washing fastness tester.

Fabrics with poor washing fastness should be dry-cleaned. But if they must be wet-washed, then other washing conditions may need to be tweaked and watched closely. For instance, the washing temperature should not be relatively high, and the washing time should be kept brief.

3.5. Color Fastness to perspiration

The Color Fastness to perspiration refers to the degree of color fading of a dyed fabric after small perspiration.

3.6. Ironing Color Fastness

This refers to the extent dyed fabrics may discolor or fade from ironing.