White and pastel garments leave the factory clean. Weeks later, after storage in polybags and cartons, they arrive with yellow edges and yellow fold lines — often worst where the garment touched the bag or the cardboard.
Nobody washed or wore them. The usual suspect is phenolic yellowing, and ISO 105-X18 is the screening test for it.
What phenolic yellowing is
ISO 105-X18:2007 defines it as discolouration of textile materials caused by the action of oxides of nitrogen and phenolic compounds, which together produce a yellow colour. Phenolic antioxidants are common in packaging films and other materials around a garment; nitrogen oxides come from the air, for example from combustion exhaust.
The standard is careful about its own limits. It covers phenolic yellowing only, not the many other causes of yellowing in textiles. And it is a screening test: passing it does not guarantee that the material will never yellow. Its value, as the standard notes, is that in practice it significantly reduces complaints by flagging materials that need corrective action.
How the test works
The method builds a sealed package and bakes it:
| Element | Requirement in ISO 105-X18:2007 |
|---|---|
| Glass plates | (100 ± 1) mm × (40 ± 1) mm × (3 ± 0.5) mm; seven per package |
| Test papers | (100 ± 2) mm × (75 ± 2) mm cellulose, treated with a small amount of 2,6-di-tert-butyl-4-nitrophenol; one folded paper per sandwich |
| Specimens | Up to five per package |
| Control fabric | (100 ± 2) mm × (30 ± 2) mm white polyamide known to yellow in this test; one per package, always |
| Wrapping | Three layers of BHT-free polyethylene film, about 63 µm, sealed airtight with tape |
| Load | (5 ± 0.1) kg in a stainless steel test device |
| Incubation | 16 h ± 15 min at (50 ± 3) °C, device placed on its side |
| Assessment | Within 30 min of opening, with the grey scale for staining (ISO 105-A03) or instrumentally (ISO 105-A04) |
Each specimen and the control fabric sit inside a test paper folded along the 100 mm axis, and the six sandwiches are separated by glass plates. The test device is the same type of stainless frame with a closely fitted 5 kg weight used in perspiration testing.
The control fabric is the validity check
The single most important rule in the standard is easy to skip: assess the control fabric first. It must have yellowed to at least grade 3 on the staining grey scale. That proves the test papers were active, the package was airtight and the temperature was right.
If the control fabric has not yellowed, the test has not worked. Every specimen in that package — including the ones that look perfectly white — has no result. Repeat with new materials.
A lab that reports "grade 5, no yellowing" without a yellowed control fabric next to it has not shown that the specimen resists phenolic yellowing. It has only shown that nothing happened in the oven.
Where the test goes wrong
Old or badly stored test papers
The papers are consumables with a shelf life. The standard asks for them to be stored in resealable aluminium foil packaging in a cool, dry place or conditioned lab, and used within six months of opening. New papers and new control fabric are used for every test. Papers left in an open drawer lose their effect, and the control fabric will tell you — if you check it.
The wrong film
The polyethylene film must be BHT-free. BHT (butylated hydroxytoluene) is itself a phenolic antioxidant used in many films. Wrapping the package in ordinary kitchen film or a production polybag adds an uncontrolled source of the very compound the test is trying to dose.
A leaking package
Three firm layers, sealed with tape, airtight. The method depends on a closed package; a loose wrap is a different exposure, and its result cannot be compared with a correctly sealed one.
Fewer plates for fewer specimens
If fewer than five specimens are tested, the package still uses seven glass plates, and the control fabric is still included. The geometry and load stay the same.
Late assessment
Assess within 30 minutes of opening. The standard warns that the colour change may fade rapidly in air on some materials. A package opened at the end of the day and graded the next morning under-reports yellowing.
Dirty plates
Clean the glass plates between tests with a cleaner that leaves no residue, such as alcohol. Residues from the previous run can carry over.
Reading the result
Staining is assessed against the original material from which the specimen was cut, using the grey scale for staining under the viewing conditions of ISO 105-A01 — in practice, a light cabinet with a daylight source. The report gives the numerical staining grade as the expression of the material's potential to phenolic yellowing.
Remember that a poor result points at the material, not necessarily at the packaging: the test asks whether the textile is susceptible when phenolics and nitrogen oxides are present. The chemistry left on the textile by dyeing and finishing can influence that susceptibility, so a failing result is a conversation with the finishing department as much as with the packaging supplier.
Checklist
- Test papers within six months of opening, stored in foil?
- New papers and new control fabric for this test?
- BHT-free film, three layers, airtight?
- Seven plates, 5 kg, 16 h at 50 °C?
- Control fabric ≤ grade 3 before anything else is graded?
- Specimens assessed within 30 minutes of opening?
TLI-TexLabInstruments manufactures its perspiration fastness tester, which also lists ISO 105-X18 among its methods, in its own workshop in Istanbul.