Washing fastness testing
Washing fastness is the measure of what a dyed textile does when it is laundered. Two things are assessed at the same time: how far the shade of the specimen itself changes, and how much colour transfers onto the fabrics laundered alongside it. A reactive dye that has fixed properly to cellulose resists both, because the dye is bonded to the fibre rather than sitting on it. Unfixed or hydrolysed dye behaves differently, and it is that fraction the test exposes.
What washing fastness measures
The property matters commercially before it matters technically. A garment that bleeds onto a lighter fabric in the same wash produces a customer complaint, and a shade that shifts after five home washes is a rejected lot. Buyers in the apparel, home-textile and uniform trades therefore treat washing fastness as a gate rather than a preference, and it is usually the first fastness property written into a dyehouse order.
The reference Nuchem follows
Nuchem runs the washing fastness test to ISO 105-C10:2006, Test C. The conditions are stated in full on the method sheet, so a Nuchem result can be compared with a result from another laboratory only when that laboratory works to the same test letter and parameters.
| Test method | Test no. | Temperature | Detergent | Sodium carbonate | Liquor ratio | Steel balls | Time (min) |
|---|---|---|---|---|---|---|---|
| ISO 105-C10:2006 | C | 60 °C ± 2 °C | 5 g/l | 2 g/l | 1:50 | None | 30 |
How the test is run
The method uses a Launder-Ometer, a specimen of the dyed fabric, and a multifibre adjacent fabric carrying bands of the fibre types a garment is likely to be washed with. The sequence below is the one followed in the Nuchem laboratory.
- A specimen 4 cm × 10 cm is cut from the dyed fabric.
- The specimen is attached to a multifibre fabric of the same size at one corner.
- A solution of 5 g/l ECE detergent and 2 g/l sodium carbonate is prepared.
- The specimen and multifibre fabric are placed in the solution in the Launder-Ometer at 60 °C for 30 minutes.
- The specimen is rinsed with warm water.
- Excess water is squeezed out with cold water and the specimen is dried.
- Staining and change in colour are measured on the grey scale and recorded in a test report.
How the result is read
Change in colour and staining are graded separately on the grey scale, in half grades from 1 to 5, where 5 is no perceptible change. Change in colour is judged against an unwashed specimen of the same fabric. Staining is judged band by band against the multifibre strip, so a single test can return one change-in-colour figure and several staining figures, one for each fibre type in the strip.
The agreed values for each published COTFIX grade are listed on the fastness and solubility data page. Because deep shades and certain colour chemistries carry unfixed dye differently, the per-grade table rather than a series average is the authority for a named dye.
Frequently asked questions
A washing fastness test run at 60 °C for 30 minutes at a liquor ratio of 1:50, with 5 g/l detergent and 2 g/l sodium carbonate and no steel balls. The letter denotes the severity of the wash conditions.
Because a garment is laundered with more than its own fibre type. The strip carries bands of several fibres, so one test shows which of them the dye would stain.
It means no more than a half-grade of change under the conditions of this test. Real laundering varies in temperature, detergent and load, so the rating is a comparative measure rather than an absolute guarantee.
Yes. The specimen is rinsed, squeezed and dried, then graded against an unwashed specimen of the same fabric.
The laboratory runs the test at the conditions a buyer's order specifies. Test C is the condition Nuchem publishes, and a different severity should be named in the enquiry.
Need a washing fastness figure for a specific shade?
Give the COTFIX grade and the wash conditions the buyer's order specifies, and the laboratory will run the test and report the change in colour and the staining.