Fabric defects · Woven fabric - Denim fabric defects: from the indigo range to the loom

Most denim is a cotton twill with an indigo-dyed warp and a white filling. Many of its defects are ones any woven fabric can have. Its indigo warp adds its own: range stops, uneven dyeing, and shade that drifts from lot to lot. Because denim garments are washed after they are sewn, small differences in the dyeing show.

Fine diagonal twill lines with a band across the width, the way an indigo range stop shows, outlined in cyan.

What ConductVision Textile records

ConductVision Textile is designed to flag each defect with its place on the roll, its size, its points and a still image. Your inspector names the defect and confirms or dismisses it.

On the defect map in the roll report, each denim defect keeps its own shape: a spot, a line along or across the roll, or a band.

ConductVision Textile does not measure bow, skew, width or shade.

Fabric inspectionDefects, points and a final points forecast

What denim is

Cotton Incorporated's textile glossary describes denim as a cotton fabric of warp yarns "dyed continuously with blue indigo dye and filling yarn which is kept white" ¹. As a rule it is woven as a 3/1 or 2/1 twill, or a 3/1 or 2/2 broken twill ².

Indigo has a very low affinity for cotton, so it stays in the outer layers of the yarn and leaves "an intense ring of color around a white core." With most other dyes, that ring would count as a dyeing defect ².

Most denim is yarn-dyed, with the warp dyed in indigo and the filling left undyed. Since denim garments came to be washed after they are made, the consistency of indigo dyeing has become "crucially important" to their quality ².

Denim defects by stage

They run in order from spinning to garment washing. Most are denim examples from Cotton Incorporated's defect glossary ³.

Denim defects by stage
Defect	What it is
Thick places	Two ends of roving that run into one end of filling in spinning make a yarn twice its normal size, which shows as a thick place ³. Some denims carry slubs on purpose, in the filling or in the warp ¹.
Color fly	Small amounts of colored fiber spun into yarn of another stock, from reworked waste or from colors run close together without enough care to keep them apart ³.
Uneven dyeing on the range	Dirt, minerals, ash, pectin and natural waxes have to come out in the scouring baths for even wetting and dyeing. A rope of yarn dried too fast draws the dye to its surface ².
Glazed yarn	Drying cans that are too hot can overstress the yarn, "producing an undesirable glazed appearance that reduces absorbency in later processing" ².
Indigo dye range stop	A machine stop on the indigo range. In Cotton Incorporated's example, the stop shows as "a filling wise band of approximately fifteen inches" ³.
Shade from lot to lot	To keep color even between garment panels after washing, denim makers use sequential dyeing. It is based on the idea that indigo yarn dyed at one time most closely matches the yarn dyed just before and just after it ².
Dye streaks from sizing	Size protects the indigo from rubbing off in weaving. Too little size lets the yarn abrade, "resulting in dye streaks," clinging, and broken and tangled ends ².
Ends out	A missing end leaves "a thin dark line on the face of the fabric with short filling floats on the back" ³.
Open reed	A bent reed wire holds the warp ends apart and exposes the filling ³.
Ends woven without tension	An end that broke far back on the loom and was woven in without tension puckers as it goes into the cloth ³.
Drawbacks	Excess tension builds up behind some abnormal restriction, and when the restriction clears, the extra yarn is woven in gradually. Drawbacks can run from inches to yards and often break ends. In a small drawback, a mat-up behind the harness pulls the ends taut, and the undyed filling takes over the face ³.
Temple bruise	Discoloration where the loom temple scuffed or abraded the fabric ³.
Mispicks	One pick of filling missing. How it looks depends on the weave ³.
Floats	A knot with long ears now and then interferes with the interlacing of warp and filling on its way through the harness, leaving filling floats. On a shuttle loom, a shuttle thrown out of the shed leaves filling floating on the face, an overshot, or on the back, an undershot ³.
Knots	A spooler knot left in the yarn ³.
Double ends	An extra end woven into the fabric makes small, flat distortions in the twill line ³.
Kinky filling	Filling that twists on itself, from too much twist in the yarn or, on a shuttle loom, a shuttle not boxing properly, a faulty filling fork or too much power on the picker stick ³.
Wavy cloth	A let-off that does not work properly lets the warp tighten and ease by turns, which makes thick and thin places ³. Together, the let-off and take-up speeds set the picks per inch ².
Poor cover	Loom settings that let too much filling show through give a chopped look. Set properly, the warp dominates and forms a smooth face of clear twill lines ³.
Buttonhole selvedge	Tension built up in the shuttle pulls the filling taut, draws the selvedge toward the body of the fabric, and splits the shed near the edge ³.
Mixed filling	A bobbin of lightweight filling subdues the twill line and changes the shade. On a 3/1 left hand twill it shows more from the back ³.
Starting marks	Many loom stops come from improper tying-in of the warp ². A stop or start can leave a band across the full width or part of it, with picks thicker or thinner than normal, or more or fewer of them ⁴.
Abrasion streaks	In garment washing, garments can be turned inside out to cut unwanted abrasion streaks, especially when creases are pressed in ⁵.

What causes denim defects

After weaving, greige denim is normally singed, finished with starch and a lubricant, and then mechanically shrunk ⁵.

What causes denim defects
Stage	What happens	What to check
Spinning	Colored fiber spun into another stock gives color fly, and two roving ends running into one end of filling give a doubled, thick yarn ³.	Waste rework, and colors kept apart in spinning
Indigo dyeing	Impurities the scouring baths fail to remove, ropes dried too fast, or drying cans too hot ². A stop on the range leaves a band ³.	Scouring baths, drying speed, can temperature and range stops
Beaming	Crossed, lost or tangled ends on the beams, or yarns wound onto a section beam at unequal tension ².	Ends and tension on each section beam
Sizing	Too much size chafes the yarn and sheds size at the loom. Too little lets the yarn abrade into dye streaks and broken ends ².	How much size goes on
Weaving	Improper tying-in of the warp causes many loom stops ². Bent reed wires, temples, knots with long ears and loom settings leave open reeds, bruises, floats and poor cover ³.	Tying-in, reed wires, temples and loom settings
Filling supply	Alternating picks from different filling packages helps break up repeating yarn defects in any one package ².	Picks alternated between packages
Garment washing	Abrasion in garment washing can leave streaks. Turning garments inside out cuts them, especially when creases are pressed in ⁵.	Garments turned inside out

Where denim defects show on a roll

Some denim defects have a known place. Kinky filling "is most common approximately eight to ten inches in the selvage and is erratic in its placement," and when a center filling fork causes it, "the kinks will appear in a line down the center of the fabric" ³.

A buttonhole selvedge may occur in isolated instances or "continuously with the running out of each bobbin," depending on its cause ³. An indigo range stop shows as a filling wise band, across the fabric, while an end out leaves a thin line along it ³.

Defect positionWhat a defect's place on the roll points to

How denim defects count

Point limits for denim are set by the buyer. One buyer manual, which follows the 4-point system of ASTM D5430, sets them in points per 100 square yards by weight and yarn type, with a lower limit across a shipment than for a single roll ⁶.

Rolls over the limit come out of the shipment, and a shipment whose total is over its limit is rejected. Every order is also checked for shade: a swatch from every roll is compared within its lot in a lightbox kept from ambient light, and the rolls are marked by shade group. Roll to roll shading counts as a continuous defect, with up to 4 points for each yard or metre of the shipment that has it ⁶.

Cotton Incorporated's defect glossary rates its denim examples of an end out, an open reed and an indigo range stop major, and a knot and a double end minor ³. Its grading guide defines a major defect as one severe enough, if exposed, to make the end item a second ⁷.

Sources

Pilot - How a pilot starts

We start with recorded video of your inspection frame and agree with your team on one fabric to test. The pilot runs for a set time, and before it starts we agree on what counts as success. For each defect it marks, ConductVision saves a still image and its place on the roll on your network for your inspector to check.

You bring: Recorded video of fabric running over your inspection frame
We set up: One fabric, and the limit you grade it against
You get: Marked defects, running points and a final points forecast for each roll, and a results report checked against what we agreed

One question to start with

Which denim style shows the most defects?

Plan a pilot