Colour Fastness Testing for Knit Bags: Which ISO 105 Part Covers Which Risk, and How to Write the Ratings into a Purchase Order

The Risk List First: Six Ways a Bag Loses or Transfers Colour

Colour fastness is not one property. It is a family of behaviours, and each one has its own method because each one is caused by a different mechanism. A bag can be excellent against light and poor against rubbing, or excellent dry and poor wet, and a single generic colour fastness clause cannot express either.

Start by listing the exposures the bag will actually meet. A shopper carried against a light coat risks colour transfer by rubbing. A beach bag risks light, water and chlorine. A bag sold with a care instruction risks laundering. A backpack risks perspiration against a shirt. Each line on that list maps to a different part of ISO 105.

The reason to do this in order is that it stops over-testing. Most bag programmes need three or four parts, not twelve, and a laboratory asked for a full colour fastness panel will run many more methods than the bag will ever meet in service. The risk list is what keeps the testing proportionate.

Checklist: Assigning an ISO 105 Part to Each Risk

1. Carried against clothing: rubbing, dry and wet. Use ISO 105-X12, or AATCC 8 on a crockmeter for North American programmes.
2. Sold with a wash care instruction: laundering. Use ISO 105-C06, or AATCC 61 for the accelerated route used in North America.
3. Displayed in daylight or used outdoors: light. Use ISO 105-B02 with a xenon arc source, rated against blue wool references 1 to 8.
4. Caught in rain or used at the beach: water. Use ISO 105-E01, with ISO 105-E02 for sea water where the bag meets it.
5. Worn against the body: perspiration. Use ISO 105-E04 with acidic and alkaline artificial perspiration solutions.
6. Dark colourway against a pale lining or trim: staining onto adjacent material. Check the multifibre staining result from the laundering test.
7. Printed or panel-joined designs: colour transfer between panels. Test the assembled construction, not a single-colour swatch.
8. Bleach or chlorine exposure: ISO 105-C06 variants with bleach, or the relevant part for chlorinated water where the bag will meet a pool.

Eight lines, and most bag programmes need the first four. The value of writing them down is that the specification then names a part for each exposure, so a report can be checked against it rather than merely accepted as a colour fastness pass.

Rubbing Fastness: ISO 105-X12 and AATCC 8

Rubbing, or crocking, is the test most bag programmes need first, because a bag rubs against clothing constantly and the complaint is visible immediately. ISO 105-X12 rubs a white cloth over the specimen under controlled conditions, once dry and once wet, and rates the staining of the cloth against a grey scale.

AATCC 8 is the North American equivalent, run on a crockmeter, and AATCC 116 covers rotary rubbing for smaller or irregular areas. The methods are broadly comparable in principle but not identical in stroke, force and cloth, so results should not be converted between them.

The pattern buyers need to expect is that wet rubbing rates lower than dry, commonly by one to two grades on a dark shade, because moisture helps loosely held dyestuff detach. Setting one minimum rating for both conditions effectively sets the requirement at the wet figure, which is correct for a bag but worth stating deliberately.

Rubbing

ISO 105-X12, dry and wet, rated against the grey scale for staining

Rubbing, AATCC route

AATCC 8 on a crockmeter, AATCC 116 for rotary rubbing on small areas

Laundering

ISO 105-C06, with single and multiple test variants at defined temperatures

Laundering, AATCC route

AATCC 61, accelerated, with numbered conditions representing home washes

Light

ISO 105-B02, xenon arc source, rated against blue wool references 1 to 8

Water

ISO 105-E01, with ISO 105-E02 for sea water

Perspiration

ISO 105-E04, acidic and alkaline solutions

Rating scale, staining and change

Grey scale 1 to 5, with half steps, 5 being no change

Rating scale, light

Blue wool 1 to 8, higher being better

Laundering Fastness: ISO 105-C06 and AATCC 61

Laundering fastness measures two things at once: the colour change in the specimen itself, and the staining of adjacent material. The adjacent material is a multifibre strip combining several fibre types in one strip, so a single test shows which fibre the dye tends to migrate onto.

ISO 105-C06 offers single and multiple test variants at defined temperatures and chemical intensities, and the multiple variants are more severe because of increased mechanical action. AATCC 61 uses numbered conditions designed to approximate a given number of home launderings in an accelerated cycle. The two serve the same purpose and should not be converted one to one.

For a knitted bag the common cause of a poor laundering result is residual hydrolysed dyestuff left after inadequate washing following dyeing. That is a process issue rather than a dye selection issue, which is why a failed laundering test is often fixable without changing the colour at all.

Light Fastness: ISO 105-B02 and the Blue Wool Scale

Light fastness is rated differently from everything else in the family. ISO 105-B02 exposes the specimen to a xenon arc source representative of natural daylight alongside blue wool reference strips numbered 1 to 8, and the rating is the number of the reference whose fading matches the specimen.

That scale runs the other way from the grey scale in terms of expectation. A grey scale rating of 4 or better is the usual commercial floor for staining and change. On blue wool, a rating of 4 is unremarkable, and anything sold for outdoor or window-adjacent use typically needs materially higher.

Light fastness matters for bags more than buyers assume, because a bag left on a car seat, on a beach or in a shop window receives far more exposure than a garment worn indoors. Where a range has an outdoor colourway, test that colourway rather than the house dark.

Water, Perspiration and the Other Parts

Water fastness under ISO 105-E01 covers rain and accidental wetting, and ISO 105-E02 covers sea water where a bag will meet it. Perspiration fastness under ISO 105-E04 covers prolonged contact with skin, using both acidic and alkaline artificial perspiration solutions, and it belongs on any bag worn against the body.

Both are usually lower priority than rubbing and laundering for a tote or a shopper, and both become first-order for a backpack or a bag carried against a shirt. This is precisely why the risk list comes first: the same range justifies different test sets depending on how it is carried.

One part worth knowing about for bags with printed decoration is that a print can behave differently from the base fabric. Testing the printed area, or the assembled bag where the print sits against another panel, catches transfers that a plain swatch test will never show.

There is a commercial argument for running the wider set on the first programme even where the risk list is short. Each additional part costs a small increment against one order and produces a reference file for the whole range, so that a later question about a poolside or rain-exposed colourway can be answered from records rather than from a fresh commission and another wait.

Reading a Grey Scale Rating: What 4 Actually Means

The grey scale runs 1 to 5 with half steps, where 5 is no visible change or no staining and 1 is severe. A rating of 4 represents a slight but perceptible difference, and it is the usual commercial floor for change and staining on apparel and accessories.

Half steps matter in practice. A result reported as 3 to 4 means the assessor placed it between the two, and a specification requiring a minimum of 4 is not met by a 3 to 4 result. Writing the minimum as a whole number and requiring the report to do the same removes the ambiguity.

The other thing to understand is that grey scale assessment is a controlled comparison, not a promise that a customer will never notice anything. It is repeatable between trained assessors under defined lighting, which is exactly why it is useful, and it says nothing about whether a particular shade change is acceptable on a particular product.

Colour Fastness on a Knitted Panel Specifically

A knitted surface behaves differently from a woven one under rubbing, because the loop presents more surface area to the rubbing cloth and holds loose dyestuff at the crown where the cloth meets it first. The practical consequence is that a knit can rate lower on rubbing than a woven of the same colour and dyeing.

Structure shade is the second knit-specific issue. A knitted body and a knitted handle from the same dye lot can read as different colours because the two structures reflect light differently, and no colour fastness test detects that. It is caught by visual assessment of the assembled bag under the lighting it will be sold under.

The third is that pile and raised finishes hold more loose dyestuff at the surface. Where a bag uses a brushed or raised knit, expect wet rubbing to be the binding test in the range, and consider whether the finish is worth the rating it costs on the darkest colourway.

Writing the Colour Fastness Clause

The clause needs the ISO 105 part, the condition, the scale and the minimum rating, stated per colourway. Four fields per line, one line per exposure, and a report can then be checked line by line rather than accepted as a general colour fastness pass.

Add the colourway clause and the clause is complete. Naming the darkest colourway as the one to be tested first, and requiring the report to state which colourway was tested, prevents the common outcome where the laboratory tests whichever swatch arrived first.

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