Colour fastness and dye testing methods
Every fastness value on a Nuchem data sheet is produced by a defined laboratory method, and a number is meaningless without the method behind it. A washing-fastness rating of 4-5 is only comparable with another rating produced under the same standard, the same liquor ratio, the same detergent and the same grading scale. Two laboratories can test the same fabric and report different figures when their conditions differ, and neither result is wrong. This section sets out the methods Nuchem Dyestuffs applies to reactive-dyed textiles, the reference each method follows, and how the result is read and reported.
What a test method is, and why it matters as much as the result
The methods are written from the practice followed at Nuchem's own laboratories in Gujarat, and each page names the reference that practice follows. Where a test is governed by a published standard, the page states which standard applies and describes how Nuchem runs it. The standard's own text is not reproduced: those documents are copyrighted, and a buyer needs the practice rather than the clause.
The six tests Nuchem runs
Six method sheets are published here. Each carries the materials used, the test conditions, the procedure followed and the scale on which the result is graded. The reference column names the standard or in-house method behind the test. Where a sheet carries no external reference, the test is a Nuchem laboratory method.
- Washing fastness
- Rubbing and crocking fastness
- Perspiration fastness
- Light fastness
- Dye solubility
- Dischargeability
| Test | Reference followed | Result graded by |
|---|---|---|
| Washing fastness | ISO 105-C10:2006, Test C | Grey scale |
| Rubbing and crocking fastness | ISO 105-X12:2016 | Grey scale |
| Perspiration fastness | ISO 105-E04 | Grey scale |
| Light fastness | ISO 105-B02:2014, xenon arc | Blue wool scale, 1-8 |
| Dye solubility | Nuchem laboratory method | Solubility in g/l |
| Dischargeability | Nuchem laboratory method | Visual, against the ground shade |
How results are graded
Colour fastness results are reported on the grey scale, in half grades from 1 to 5, where 5 means no perceptible change and 1 means severe change. Two things are graded separately: the change in the shade of the specimen itself, and the staining transferred onto the adjacent multifibre strip, which is assessed band by band against each fibre type in the strip. Light fastness is reported on the blue wool scale in grades 1 to 8, which measures fading against eight reference standards rather than against a visual grey contrast, so a light figure of 6 and a light figure of 3 are not variations of the same judgement but two clearly separated degrees of fading.
Where a Nuchem method sheet carries a specification, that figure is the target the laboratory works to. A specification is a target for the grade rather than a guarantee for every shade in a series, because deep shades and certain colour chemistries carry unfixed dye differently.
Where these values appear for each COTFIX grade
Fastness and solubility values for the published COTFIX range are set out grade by grade on the fastness and solubility data page. Each row names the grade and gives the values for that dye, so a buyer can match a grade to the requirement of their own order rather than reading a series average. Where an order needs a test that is not published, the laboratory runs it for the named grade and the report is supplied with the order.
Frequently asked questions
From Nuchem's own laboratories at its Gujarat plants, following the reference named on each method page. Where a buyer's scheme requires testing by an accredited third party, that is arranged for the order.
Yes. Different liquor ratios, detergents, temperatures or grading conditions produce different numbers, and neither result is wrong. That is why a figure should always be read together with the method it came from.
Published standards are copyrighted documents sold by their issuing bodies, and reproducing them is not permitted. A buyer does not need the clause text; they need to know which standard applies and how Nuchem runs the test.
Fastness testing is run as part of product development and grade control, and on request for a specific order. A buyer who needs a report for a named grade against a named requirement should say so in the enquiry.
No. A method specification is the target for the grade. Deep shades and certain colour chemistries behave differently, so the per-grade published values are the authority for a specific dye.
Need a test report for a named grade?
Tell Nuchem the COTFIX grade, the property and the requirement the order has to meet, and the laboratory will run the test and supply the report with the order.