Wash fastness is the most-run colour fastness test in any dyehouse, and the one where two labs most often disagree. The machine is simple. The variables around it are not.
What the test does
A specimen of the dyed fabric is stitched to an adjacent white fabric — usually a multifibre strip carrying acetate, cotton, nylon, polyester, acrylic and wool in bands. The composite goes into a sealed stainless pot with a measured volume of detergent solution, a specified number of steel balls, and is rotated in a thermostatically controlled bath at a set temperature for a set time.
Afterwards you assess two separate things:
- Colour change — how much the specimen itself shifted, graded against the grey scale for colour change (ISO 105-A02).
- Staining — how much colour transferred onto each band of the adjacent fabric, graded against the grey scale for staining (ISO 105-A03).
Both are reported 1 to 5, with half steps. A single number without saying which of the two it refers to is meaningless, and staining is usually the one that fails.
Why the steel balls matter
The balls are not there to agitate. They provide the mechanical action that a domestic wash provides through fabric-on-fabric rubbing and drum tumbling. The count is specified per test condition — and it changes between conditions. Using the wrong number is the single most common reason a result cannot be reproduced at the buyer’s lab.
The same goes for liquor ratio, detergent concentration, temperature and time. ISO 105-C06 is not one test; it is a family of conditions (A1S, A2S, B1S, B2S, C1S, C2S, D1S, D2S and so on) each simulating a different wash severity. “Passed C06” on a report tells you nothing. “Passed C06 A1S, staining 4–5 on cotton” tells you something.
The instrument
A rotary wash fastness tester holds the pots in a heated water bath and turns them at the standard 40 ± 2 rpm. What you are paying for is temperature uniformity across every pot and a seal that does not leak at temperature. A pot that runs two degrees cold gives a flattering result that will not survive the buyer’s retest.
Eight pots of 550 ml covers most mill workloads and lets you run a full multifibre set in one cycle. See the Washing Fastness Tester (Launder-Ometer).
Where results go wrong
- Grading under the wrong light. Grey scale assessment is a visual comparison. Do it in a colour matching cabinet under D65, with the scale and specimen at the same angle. Bench fluorescents will cost you a grade in either direction.
- Tired grey scales. They soil and fade. Keep them in their wallet, replace them on a schedule, and never let them sit open on a bench.
- Wrong adjacent fabric. A single-fibre adjacent tells you far less than a multifibre strip, and buyers increasingly ask for multifibre by name.
- Uncontrolled drying. How the composite is dried after rinsing affects the final assessment. Fix the method and write it into your SOP.
The related tests buyers ask for next
Wash fastness rarely arrives alone. The usual set is:
- Rubbing / crocking fastness — ISO 105-X12, dry and wet
- Perspiration fastness — ISO 105-E04, acid and alkaline
- Dry heat and sublimation — ISO 105-P01, critical on polyester
Equip for all four and you can answer almost any apparel buyer’s fastness protocol without sending work out.
See the full Lab Testing Machines range, built to order in India with installation and training included.