Crockmeter Rubbing Fastness: How AATCC 8 and ISO 105-X12 Differ, Why Wet Always Scores Lower, and What to Do About Dark Knit Panels

What a Crockmeter Actually Does

A crockmeter is a deliberately simple machine. A white cotton rubbing cloth is mounted on a finger of defined diameter, loaded onto the specimen with a defined force, and drawn back and forth a defined number of times over a defined stroke. The cloth is then removed and the colour it has picked up is rated against a grey scale for staining.

The output is a staining rating only. Unlike a laundering test, the specimen's own colour change is not assessed, because rubbing is not expected to fade the fabric. This is worth stating on a specification, because buyers sometimes ask for a colour change figure from a crocking test and no such figure exists.

The machine is small, the test takes minutes, and the cost per result is low relative to any other method in the colour family. That is why crocking is usually the first colour fastness test a bag programme runs and often the only one a first order carries, which is reasonable for a tote and insufficient for anything washed or sun-exposed.

AATCC 8 Against ISO 105-X12, Point by Point

The two methods are built on the same idea and differ in detail. Both mount a white cotton cloth on a finger of around 16 mm diameter, load it at around 9 newtons, and draw it over the specimen for ten rubs across a stroke of roughly 100 millimetres. The differences are in the cloth specification, the wet pick-up level, and the way the specimen is prepared and mounted.

Those differences are small enough that the two often agree and large enough that they sometimes do not, particularly on a dark shade near a rating boundary. A result of 3 to 4 under one method can read 4 under the other, and both are correct. This is why a specification must name the method rather than a rating alone.

The second practical difference is geography. AATCC 8 is the default in North American programmes and ISO 105-X12 in European and most Asian ones, and a buyer supplying both markets should specify both rather than assume one covers the other. Running both is inexpensive and removes a recurring argument.

Rotary and Vertical: When AATCC 116 Is the Better Choice

AATCC 116 runs the same principle through a rotary motion on a vertical crockmeter, which lets a small or irregularly shaped area be tested. It is the right choice for a printed logo, a narrow woven label, a piece of trim, or any place where the area of interest is smaller than a standard flat specimen.

It is not a better version of AATCC 8, it is a different one, and results from the two should not be mixed within one specification line. Where a bag has both a large body panel and a small printed mark, the correct approach is two lines: AATCC 8 or ISO 105-X12 on the panel, and a rotary method on the mark.

There is also a method for textile floor coverings, which appears in laboratory catalogues and occasionally in bag specifications by mistake. A bag is not a floor covering, and citing that method on a bag order is a sign that a clause was copied from a template rather than chosen.

Why the Wet Result Always Sits Below the Dry One

Every buyer sees this and some treat it as a fault. It is not. Water acts as a carrier: it loosens dyestuff held at or near the fibre surface and helps it transfer to the rubbing cloth, so more colour moves when the cloth is wet. The mechanism is physical rather than a defect in the dyeing.

The size of the gap depends on shade and on how much unfixed dyestuff remains on the surface. On a pale colourway the dry and wet results are often identical. On a deep navy, a black or a saturated red, a gap of one grey scale grade is normal and two grades is not unusual.

The two methods also prepare the wet cloth differently, each to a pick-up level the method defines, and the levels are not the same. That is one more reason a wet crocking figure written for one method cannot be read as satisfying the other, and one more reason to name the method in the clause.

Machine

Crockmeter, flat reciprocating, or rotary for AATCC 116

Finger

Around 16 mm diameter

Load

Around 9 newtons

Rubs

Ten cycles over a stroke around 100 mm

Conditions

Dry and wet, prepared and reported separately

Rating

Grey scale for staining, 1 to 5 with half steps, 5 being no staining

Colour change

Not assessed; crocking reports staining only

Typical floor, dry

4

Typical floor, wet on dark shades

3 to 4, occasionally 3 on saturated colours

Specimen

The production construction, with the tested colourway named on the report

What Moves a Crocking Rating on a Knit

Four things dominate the result, and knowing them turns a failed rating into a fixable one. The first is unfixed surface dyestuff, which is the most common cause and is a washing-off problem after dyeing rather than a colour selection problem. The second is shade depth, because a deeper shade has more dye present and more of it near the surface.

The third is structure. A knitted loop presents more surface to the rubbing cloth than a flat woven of the same yarn and colour, and holds loose dyestuff at the crown of the loop where contact begins. A knit therefore typically crocks worse than a woven in the same shade, and that is a property of the structure rather than of the dyeing.

The fourth is finish. Raised, brushed and pile surfaces hold more loose material at the surface and rate lower still. Where a programme wants a brushed knit in a saturated colour, wet crocking is very likely the binding test in the whole specification, and it is worth deciding that early rather than at the report stage.

Choosing a Minimum Rating: Three Colourways, Three Answers

A single minimum across a range is the usual approach and the wrong one where the range spans pale and saturated shades. A pale natural shade will rate 4 to 5 wet without any effort. A deep navy may sit at 3 to 4 wet on a raised knit and still be perfectly saleable. Setting 4 across the board either over-constrains the dark end or under-constrains it.

The workable approach is to set the dry floor at 4 for all colourways and the wet floor per colourway band: 4 for pale and mid shades, 3 to 4 for deep shades, and 3 where a raised finish in a saturated colour is a deliberate design choice. Three lines, and each one is defensible against a retailer's question.

Where a buyer has an existing product that performs acceptably in the market, test it and use the result as the floor. A measured figure from a bag the buyer already sells is worth more than any published table, because it already includes the buyer's own tolerance for what a customer notices.

Fixes When a Dark Knit Fails Wet Rubbing

Work down the list in order of cost. First, improve washing-off after dyeing, because residual unfixed dyestuff is the most common cause and the fix changes nothing about the appearance of the bag. Second, consider a fixation or aftertreatment step, which costs a little more and usually buys a half grade or more.

Third, look at the finish: a raised or brushed surface can sometimes be reduced slightly, or a different raising intensity used, without changing the look materially. Fourth and last, change the shade, which is the most expensive option because it resets lab dips, approvals and any existing marketing material.

One option is not a fix at all and should be named as such: switching to whichever of ISO 105-X12 and AATCC 8 gives the better number. That is selecting a method to obtain a result, and it produces a bag that still marks the customer's coat exactly as before.

Reading the Report and Avoiding the Half-Step Trap

A crocking report should name the method and edition, the dry and wet results separately, the tested colourway, and the construction. Four fields, and the third is the one most often missing, which matters because a report on a pale colourway tells a buyer nothing about the navy in the same range.

The half-step trap is the second thing to watch. Grey scale ratings are given in half steps, so a result of 3 to 4 sits between the two and does not meet a minimum written as 4. Where a buyer intends to accept 3 to 4, write it as 3 to 4 rather than as 4, or the report will fail a requirement the buyer thought it met.

Conditioning matters here too, though less than in physical testing. Textiles are conditioned under ISO 139 before colour fastness testing, and a laboratory that skips it introduces variability into a test whose whole value is comparability.

Writing the Crocking Clause

The clause needs the method and edition, the dry minimum, the wet minimum, the colourway each applies to, and a statement that the tested colourway must appear on the report. Five fields, and for a buyer supplying both North America and Europe, specify both AATCC 8 and ISO 105-X12 rather than assuming one satisfies the other.

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