Color Fastness in Textiles: Testing Methods, Standards, and Equipment

Color fastness testing answers one commercial question: will the colour survive the way the product is actually washed, worn and stored, and will it stay off everything it touches? A dyed fabric that bleeds onto a co-washed garment, rubs off onto a bag strap or fades in a shop window becomes a return, a claim or a rejected shipment, even when every other specification is met.

Because colour is lost through different routes, no single test covers it. Each method simulates one route under controlled conditions and reports the result as a grade, and a specification is only enforceable when it names the method, the test code and the minimum grade.

What Color Fastness Testing Covers

Color fastness is the resistance of a dyed or printed textile to colour change, and to transfer of colour onto adjacent material, when it is exposed to a defined condition. The same test run produces two readings: change in colour of the specimen itself, and staining of the undyed adjacent fabric it was in contact with during the test.

Most fastness properties are graded on a grey scale from 5 (no visible difference) down to 1 (severe change or heavy staining), with half grades in between. Light fastness is the exception and is graded against blue wool references on a scale from 1 to 8.

Results are comparable only when the method and test code match. A report citing ISO 105-C06 A1S and a report citing AATCC 61 have both measured washing, but under different conditions, so their grades are not interchangeable.

Color Fastness to Washing: ISO 105-C06, AATCC 61 and GB/T 3921

In a washing fastness test, the specimen is sewn to a strip of adjacent multifibre fabric, placed in a sealed stainless pot with a detergent solution and, depending on the method, steel balls to add mechanical action. The pots rotate in a heated water bath for a set time; the specimen is then rinsed, dried and graded against the grey scales.

Two details change the severity of the result. ISO 105-C06 offers single (S) and multiple (M) test codes, where a multiple test is harsher because it adds mechanical action and can approximate up to five launderings. AATCC 61 works differently: one accelerated 45-minute cycle is roughly equivalent to five typical home or hand launderings. The letter in the code also sets the temperature and detergent regime, which should match the care label the product will carry.

Equipment for this test is often called a rotawash or launderometer. A color fastness tester of this type determines fastness to washing or dry cleaning, and the AT010 Series illustrates the practical details that matter in daily use: a touch-screen interface for heating temperature and running time, five built-in test programs plus three programmable ones, a 304 stainless steel working chamber, a door interlock that stops the machine when opened, and 550 ml pots for ISO and GB methods or 1200 ml pots for AATCC methods.

Color Fastness to Rubbing (Crocking): ISO 105-X12 and AATCC 8

Rubbing fastness measures how much dye transfers from the fabric surface to another material under friction. A standard white cotton rubbing cloth is rubbed against the specimen under a fixed load of 9 N for ten cycles, either dry or wet, and the staining of the cloth is then graded.

Wet rubbing is usually the harder test, because moisture allows dye to migrate more freely; dark shades such as indigo denim are the classic case where a dry grade passes and the wet grade does not. Upholstery, automotive interior fabrics and workwear specifications typically set separate dry and wet limits for this reason.

Color Fastness to Light: ISO 105-B02 and Blue Wool References

Light fastness is assessed by exposing the specimen to a controlled artificial light source, usually a xenon arc lamp, alongside blue wool reference samples. The references fade at known rates, and the specimen is graded by matching its fading to the reference that faded by the same amount, producing a value between 1 and 8.

Two sets of blue wool references are permitted under ISO 105-B02, and results from different sets may not match, so the report should state which set was used. Light fastness is graded on the 1 to 8 scale rather than the 1 to 5 grey scale, which is a frequent point of confusion when a buyer compares it with washing or rubbing results.

Perspiration, Water and Dry Cleaning Fastness

Several further tests cover the other ways colour leaves a textile. They share the same specimen, adjacent fabric and grey scale logic but change the exposure medium.

• Perspiration. ISO 105-E04 and AATCC 15 use acidic and alkaline artificial sweat solutions, with the specimen held under pressure in a perspirometer at body temperature.
• Water and sea water. ISO 105-E01 and ISO 105-E02, or AATCC 107 and 106, soak the specimen in distilled or artificial sea water and grade the change and staining.
• Dry cleaning. ISO 105-D01 and AATCC 132 use perchloroethylene in a suitable machine, which is relevant for garments labelled dry clean only.
• Chlorinated water. AATCC 162 addresses pool water, mainly for swimwear and towelling.

Reading Grey Scale Grades and Setting Pass Limits

Grades are assigned by visual comparison under standardised lighting, normally a D65 daylight source in a light box. The table below summarises what each step of the grey scale means; half grades such as 4-5 and 3-4 are used routinely.

A washing or perspiration report gives one change grade and a separate staining grade for each fibre in the adjacent fabric, for example cotton, polyamide and polyester. The lowest staining grade is the one that matters commercially, because it identifies the fibre a garment is most likely to mark in a mixed wash. Writing a limit as a method, a code and a number, such as ISO 105-C06 A1S with change 4 and staining 3-4, makes the requirement testable; writing good colour fastness does not.

Preparing Specimens and Adjacent Fabrics

Consistency in preparation is what makes grades reproducible between laboratories.

• Cut specimens to the size the method specifies and sew them to the correct adjacent fabric, single-fibre or multifibre as required.
• Condition specimens before testing in the standard atmosphere instead of pulling them straight from a humid store.
• Use distilled or deionised water of the hardness the method states, and prepare detergent solutions to the stated concentration.
• Record the number of specimens tested; a single specimen is not evidence of a batch.
• Keep grey scales in good condition and grade under the specified light source, not under mixed office lighting.

Equipment for a Color Fastness Laboratory

A working fastness section usually combines five items: a washing fastness machine for ISO and AATCC pots, a crockmeter for dry and wet rubbing, a light fastness tester with a calibrated light source, a perspirometer with a drying oven, and a set of grey scales used in a light box.

Fastness results also depend on what happened before the test. Dye class, depth of shade, fixation and the efficiency of washing-off after dyeing all influence the grade, so laboratories that prepare their own samples pair the fastness bench with sample dyeing equipment. Laboratory dyeing and finishing machine options such as infrared and jig dyeing machines reproduce production recipes at sample scale, while the wider range of fabric testing equipment covers thickness, tear strength, air permeability and other properties assessed alongside colour.

From Test Result to Production Decision

A failing fastness grade is information about a process, not only about a fabric. The usual causes sit upstream: a dye selected for the shade rather than the end use, insufficient fixation, poor washing-off of unfixed dye, or a shade so deep that the fibre is saturated. Reading the change grade and the staining grade together points to which of these is happening, and whether the fix belongs in dye selection, in the dyeing cycle or in the finishing line.

That is why fastness testing works best as a routine check on production rather than a final inspection hurdle. Tested early and reported with the method and code, it tells a mill whether a shade is commercially viable before the bulk order is dyed.