Perspiration fastness testing
Perspiration fastness measures what a dyed textile does when it is exposed to human sweat. Sweat is not simply water: it is a saline solution whose acidity varies between people, across the body and with diet, so the test is run twice, once with an alkaline solution at pH 8.0 and once with an acidic solution at pH 5.5. Each solution is applied to the fabric in contact with a multifibre strip, and both the change in the specimen's own shade and the staining of the strip are graded.
What perspiration fastness measures
The property decides whether a shade can be used next to skin. A lining, a collar, an underarm panel or a waistband sits in contact with perspiration for hours, and a dye that migrates there marks both the garment and whatever is worn over it. Buyers in apparel, sportswear, workwear and uniform supply treat perspiration fastness as a condition of the order, and because the alkaline and acidic cases can give different figures, both are usually specified.
The reference Nuchem follows
Nuchem runs the perspiration test to ISO 105-E04. Two solutions are prepared, one alkaline and one acidic, each made to a fixed composition and adjusted to a fixed pH with sodium hydroxide, because the pH of the solution is what determines how the dye behaves.
| Solution | Component | Quantity |
|---|---|---|
| Alkaline, pH 8.0 | L-histidine monochloride monohydrate | 0.5 g/l |
| Alkaline, pH 8.0 | Sodium chloride | 5 g/l |
| Alkaline, pH 8.0 | Disodium hydrogen phosphate dihydrate | 2.5 g/l |
| Acidic, pH 5.5 | L-histidine monochloride monohydrate | 0.5 g/l |
| Acidic, pH 5.5 | Sodium chloride | 5 g/l |
| Acidic, pH 5.5 | Sodium dihydrogen phosphate dihydrate | 2.2 g/l |
How the test is run
The sample and the multifibre fabric are weighed together to a total of one gram and treated in fifty millilitres of solution, a liquor ratio of 1:50. The mechanical part of the test is the load applied while the specimen dries, because that is what reproduces the pressure of a garment against skin.
- One gram of dyed sample is weighed with multifibre fabric attached, so the two together weigh one gram.
- Fifty millilitres of the acid or alkaline perspiration solution is placed in a petri dish at room temperature, giving a material to liquor ratio of 1:50.
- The specimen is kept in the solution for 30 minutes at room temperature.
- The specimen is removed and excess water is taken off with filter paper.
- The specimen is placed between two glass or acrylic plates with a 5 kg weight on top.
- It is dried in an oven at 37 °C for four hours with the plates and weight still in place.
- The sample is then hung to dry in warm air in an oven at 60 °C.
- The sample is removed, cooled, and the change in colour and the staining of the multifibre are assessed on the grey scale.
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 untreated specimen of the same fabric, and staining is judged band by band against the multifibre strip, so one test returns a change-in-colour figure and a staining figure for each fibre type in the strip. Because the alkaline and acidic solutions are run as separate treatments, a single shade carries two sets of figures rather than one.
The agreed values for each published COTFIX grade are listed on the fastness and solubility data page. Where the alkaline and acidic results differ, both are reported, because an order that specifies perspiration fastness usually names the condition it applies to.
Frequently asked questions
Because human sweat varies in acidity. An alkaline solution at pH 8.0 and an acidic solution at pH 5.5 are both tested, and a shade can perform differently in each.
The 5 kg load reproduces the pressure of a garment held against skin during drying. Without it the test would not represent the way a collar or waistband actually behaves against the body.
No. The solutions, the temperature and the mechanical conditions are all different, and the two properties are specified separately on an order.
It varies with the dye and the shade, which is why both are run rather than assuming one is always the tighter case.
Selection between grades is made on the fastness values published for each, and where an order needs a figure that is not published the laboratory tests the named grade and reports it.
Need perspiration figures for a skin-contact shade?
Give the COTFIX grade and whether the buyer's order specifies the alkaline or acidic condition, and the laboratory will run both and report the figures.