Colourfastness is a fabric's ability to keep its colour when it is washed, rubbed or exposed to light. It is tested under the ISO 105 series, and the result is a grade from 1 to 5 for washing and rubbing, where 5 means no change, and from 1 to 8 on the blue wool scale for light. For a purchasing manager buying woven fabric from India, these grades are the difference between a shirt that still looks new after twenty washes and a complaint from your customer about a white collar turned pink.
Each test looks at a different kind of stress. Washing fastness covers colour loss and staining of adjacent fabrics during laundering. Rubbing fastness, also called crocking, covers colour that transfers when the fabric rubs against another surface, dry or wet. Light fastness covers fading under daylight or a lamp that imitates it.
The three tests in plain terms
- Washing (ISO 105-C06, AATCC 61): a specimen is washed with a multifibre strip at a set temperature. Two grades are reported, one for colour change and one for staining of the strip.
- Dry and wet rubbing (ISO 105-X12, AATCC 8): a white cotton cloth is rubbed across the fabric a set number of times, once dry and once dampened. Colour transferred to the cloth is graded against a grey scale.
- Light (ISO 105-B02, AATCC 16): the fabric is exposed to a xenon arc lamp alongside blue wool references, and the fading is matched to the reference that faded by the same amount.
What grades to ask for
Most buyers set a minimum of grade 4 for colour change in washing and for dry rubbing. Wet rubbing is harder to achieve on dark shades such as indigo, navy and black, so a minimum of 3 to 3.5 is the usual expectation there. Light fastness requirements depend on the end use; shirting usually sits at 4 or above on the blue wool scale, while curtains and outdoor items need more.
Put the grades in writing on the purchase order, with the standard and method, and state which shades the wet rubbing exception applies to. A mill that accepts a vague "good fastness" has accepted nothing. Grey scale assessment is done by eye against reference cards, so results from two labs can differ by half a grade, and agreeing on one lab in advance avoids arguments.
Where fastness problems usually come from
Poor washing fastness often traces back to insufficient washing off after reactive dyeing, which leaves loose dye on the fibre surface. Wet rubbing failures on dark shades are common when the dye is heavily loaded or the finishing adds a surface film. Light fastness is mainly a property of the dye class chosen, so a cheaper dye selection at the lab dip stage shows up as fading months later. Testing the bulk fabric, not only the lab dip, is what catches these.
How we handle fastness checks
We send sealed samples cut from the bulk rolls to an NABL-accredited lab and report the grades against your specification before the goods are loaded. We also check the mill's own lab reports during our visits. If you want a second opinion on your fastness requirements, we offer a free 20-minute sourcing review.