How to Test and Assess Colorfastness of Textile?

Colorfastness, also known as dye fastness, refers to the fading or color change of textiles during use and storage due to light, perspiration, rubbing, washing, ironing, etc. The colorfastness test is a routine test for the intrinsic quality of textiles and is generally based on the color change of the specimen and the staining of the adjacent fabric to assess the colour fastness level of the textile.

How many common colorfastness tests of textiles are there?

Depending on the application environment of the textile fabric in the actual production and application process, colour fastness of textile mainly includes light fastness, washing fastness, rubbing fastness, perspiration fastness, etc.

1 Light fastness test of textile

Light fastness refers to the degree of colour change of dyed fabrics by the action of light. The test method can be used for both daylight and artificial light exposure. The textile specimen is exposed to artificial light with a group of blue wool specimens under the prescribed conditions. Assess the light fastness by comparing the degree of colour change of the two after exposure to light. The European standard is divided into 8 levels, with 8 being the best and 1 the worst; the American standard is divided into 5 levels, with 5 being the best and 1 the worst.

2 Colorfastness to washing

Colorfastness to washing is the most common colorfastness test of textile. Colorfastness to washing refers to the degree of fading of the coloured fabric after washing under specified conditions. It consists of the evaluation of the fading of the original sample and the staining of the white fabric. As is fading refers to the fading of the coloured fabric before and after washing. White fabric staining refers to the staining of white fabric after washing when the white fabric and the coloured fabric have been sewn together in a certain way and the coloured fabric has faded. Observe the degree of fading or staining under a specified light source and assess it with a standard grey scale. The result are graded on a 5-point scale, with 5 being the best and 1 being the worst.

3 Colorfastness to crocking / rubbing

The rubbing fastness test is a test in which the coloured specimens are rubbed against a dry and a wet rubbing cloth and then assess the degree of staining of the cloth. The test results are divided into 5 levels, with level 5 being the best and level 1 the worst. Although the test process is simple, it is the most basic test for colour fastness of textile products and is one of the items that buyers from almost every country must assess when placing orders. The technical conditions for the rubbing fastness test are very similar from country to country, but there are some differences.

4 Colorfastness to perspiration

The colour fastness to perspiration reflects the color change of the textile itself and the staining of the adjacent fabric in different test solutions containing histidine under the combined effect of pressure, temperature. As the composition of the artificially prepared sweat solution varies, the colour fastness to perspiration is generally assessed in combination with other colour fastnesses. The results are divided into 5 levels, 5 being the best and 1 being the worst.

6 Color fastness to sublimation

Color fastness to sublimation refers to the sublimation of dyed fabrics in storage. Sublimation fastness is assessed by using grey scale to assess the degree of color change, fading and staining of the fabric after the dry heat pressing treatment. The colour fastness to sublimation is divided into five grades, with grade 1 being the worst and grade 5 being the best. This test is generally used for disperse dyed polyester fabrics.

In addition, there are weather fastness, saliva fastness, ironing fastness, dry cleaning fastness, etc. These fastnesses put forward increasingly high requirements for the printing and dyeing process of textiles. Generally speaking, fabrics with a color fastness of 3 to 4 levels can only meet the needs of wearing.

How to assess the colorfastness of textiles?

The fading or transfer of the colour of dyed textiles can be assessed by means of a colour fastness test, the results of which are generally assessed in two ways: staining and color change.

The transfer of some of the dye from the original attached fibres to other adjacent fabrics is called staining. Staining is a function of how much of the sample colour has been applied to the standard adjacent fabric, or how much the adjacent fabric has changed colour.

Colour change is a phenomenon in which the dyed textile is subjected to various environmental factors that cause a change in colour, hue and brightness as part of the dye is removed from the fibre, or the luminous group of the dye is destroyed or a new luminous group is created. The assessment results will vary depending on the adjacent fabric and the grading method.

Colour fastness is assessed using the colour change grey scale and the staining grey scale. The grey scale currently in use are the AATCC grey scale, the ISO grey scale and the JIS grey scale. The grey scale differ slightly in their shades of grey.

Grey scale for assessing color change: original grey scale versus decreasing grey scale contrast card, 5-step, 9-grade system, grade 5 best, grade 1 worst, with half-grade rating in between, e.g. grade 4-5, grade 4, grade 3-4.

Grey scale for assessing staining: original whiteness versus increasing grey scale, 5 steps, 9-grade system, 5 being the best and 1 the worst, with a half grade in between, e.g. 4-5, 4, 3-4.

grey scale for assessing color change
grade	CIELAB color difference	tolerance
5	0	0.2
4-5	0.8	±0.2
4	1.7	±0.3
3-4	2.5	±0.35
3	3.4	±0.4
2-3	4.8	±0.5
2	6.8	±0.6
1-2	9.6	±0.7
1	13.6	±1.0
grey scale for assessing staining
grade	CIELAB color difference	tolerance
5	0	0.2
4-5	2.2	±0.3
4	4.3	±0.3
3-4	6.0	±0.4
3	8.5	±0.5
2-3	12.0	±0.7
2	16.9	±1.0
1-2	24.0	±1.5
1	34.1	±2.0
Note: The above data are from ISO 105 A02 grey sample card for assessing color change ISO 105 A03 grey sample card for assessing staining

As can be seen from the above data, the gradient decreases in the form of 1:2:4:8:16. The grey scale looks at the gradient level of the colour change, so it is important to get this gradient level of change right when grading.

How to assess the colorfastness rating of textiles?

For the rubbing colour fastness rating, wait until the wet rubbing cotton has dried, stick off any excess fibres that may affect the rating, then place three layers of cotton on the back of each rubbing cloth being rated and finally use the grey sample card to assess the degree of staining.

Soap fastness, water fastness, perspiration fastness, saliva fastness and seawater fastness: for these colour fastness tests, a reference sample of the original and an untested adjacent fabric are used to assess the color change of the sample and the staining of the adjacent fabric.

Color fastness to light: In the light fastness test rating ISO 105 B02, for example, one sample and two sets of blue wool reference are jointly exposed to the light. The exposed samples are then graded against the blue wool reference. The rating is made by matching each stage of the sample to the blue wool reference, and if different stages give different grades, the arithmetic mean of the grades of the different stages can be used to make the grade rating.

Colour fastness to light and perspiration compound: expose the sample to light with a blue wool reference to the end of the exposure, using ISO 105 B07 as an example. At the end of the test, wash and dry the sample, and then assess the color change using a grey scale.

How to use the grey scale correctly when assess colorfastness?

As shown in the diagram, the cover up card used for grading has small holes for assessing multi-fibre fabric staining, rubbing colour fastness staining and general staining. The use of cover up card allows us to focus our attention on the sample to be graded, while covering up other areas to prevent other colours from affecting our vision.

When grading, the original sample needs to be stitched together with the sample to be graded, keeping a minimum gap to prevent the colour of the backing from showing through and interfering with vision. Use the cover up card to cover the perimeter of the original sample and the sample to be graded and keep it at the same level as the graded grey card.

Light source: generally use D65 light source. The lamp life of the light source is 2000 hours. Other light sources specified by the customer are also possible, such as F light sources, 84-P light sources, UV light sources, etc.

Darkroom: The grading should be carried out in a darkroom with constant temperature and humidity. The walls of the darkroom and its wall items should be painted in a neutral grey colour, approximating to a grading grey card grade 1 to 2 (approximating to the Monsell colour card N5). As shown above, the walls are painted a neutral grey when the lights are on on the left, and when the lights are off on the right, the entire darkroom is required to be free of any light source other than that of the grading light box. And ensure that no other debris is present on the grading table.

Grading angle: grading a sample using a grey scale requires the correct grading angle. The standard requires the sample to be at 45° to the horizontal, the grading light source to be at 45° to the sample and the grader’s eyes to be at 90° to the sample. The distance between the eye and the sample is 50-70cm.

When grading, ensure the following:

• Ensure that the weave pattern of the measured and unmeasured sample is in the same direction (some warp knitted fabrics may not have a very visible weave pattern).
• For multi-coloured fabrics, e.g. striped fabrics, the stripes and the colour sequence should be in the same direction.
• Multifibre fabric: trim the edges of the multifibre fabric neatly, leaving the largest possible piece adjacent to the relevant test sample pinned to the card. Make sure that the heavily stained side is facing upwards.
• Cotton cloth for the rubbing fastness test: trim the edges of the tested cotton cloth neatly. As the colour staining is rated against the surrounding cotton, the lining area should be as large as possible. To avoid poor results due to wrinkling of the test sample, the cloth must be stapled to the white card on both sides so that there is a slight tension on the cloth.

Assessor requirements

• The assessor is not colour blind and is able to test with a colour blindness test chart card or the Farnsworth-Munsell 100 hue test kit.
• The assessor are advised to wear grey clothing, no brightly coloured clothing, no bright nail polish, and any items that may reflect light. Also, don’t wear coloured glasses.
• Do not assess when you are tired or ill. Grading is a subjective act and mood affects the psychological subjective judgement of color.
• The observer must be acclimatised to standard light conditions for at least 2 minutes before observation. The eyes are allowed to adjust to the current light environment.
• The assessor should pass a training and assessment. For different personnel, gaze calibration of the same sample should be carried out from time to time to minimise errors.

Care and maintenance of grey scale

• Keep the grey scale clean and it should be put into its packaging sleeve after use.
• The grey scale should always be checked for finger marks and must be replaced if the marks are found to have interfered with the grading.
• Try to avoid physical damage from touching and replace the grey scale if it has an effect on the rating.