Fastness is a dyed material's ability to keep its colour, and not stain other materials, under real conditions. The properties a dye should meet depend on the end product, so start from your customer's quality standard.
Fastness depends on the dye, the depth of shade, the fibre and the dyeing and finishing. A dye cannot be given a fastness grade on its own; it must be tested on dyed material.
This is why a supplier's shade card is only a starting point. The card shows results under the supplier's conditions, often at a standard depth on a standard fabric. Your fabric, your depth and your finishing can give different results.
Main tests
Most buyers use the ISO 105 series or the matching AATCC methods in the United States. The common tests are these:
- Wash fastness, for example ISO 105-C06, measures colour change and staining on adjacent fabrics after a set wash.
- Light fastness, for example ISO 105-B02, exposes the sample to a xenon arc lamp and compares it with blue wool references.
- Rubbing fastness, ISO 105-X12, measures staining on a white cloth rubbed dry and wet.
- Perspiration fastness, ISO 105-E04, uses acid and alkaline test solutions.
- Water, chlorinated water, sea water and sublimation tests apply where the end use needs them.
How results are graded
Colour change and staining are graded on grey scales from 1 to 5, where 5 means no change. Light fastness is graded against blue wool references from 1 to 8, where 8 is best. Half grades such as 3–4 are common.
Your customer's standard usually sets a minimum for each test. Childrenswear, workwear, swimwear, upholstery and outdoor fabrics each have different needs. A curtain needs high light fastness. A swimsuit needs chlorine and sea water fastness. Polyester sportswear needs sublimation and wash fastness that survive heat-setting.
Dark shades are usually harder to pass. If you sell navy, black or deep red, test those shades first, because they show weak wash and rubbing fastness soonest.
What to ask a dye supplier
- Ask for fastness data on your fibre, at the depths you dye, using the methods your customer names.
- Ask whether results were obtained with an after-treatment or fixer, and which one.
- Ask for test reports from an accredited laboratory for key shades, not only the supplier's own card.
- Ask for results in the same units your customer uses, so ISO and AATCC grades are not mixed up.
- Recheck fastness on bulk lots now and then, not only on the first sample.
- Ask what changes the supplier makes when a raw material changes, since a new intermediate can shift fastness slightly.
Next step
Fastness belongs in your dye specification and, where useful, on the dye COA. We check supplier data and arrange independent tests. To start, book a free sourcing review.