Denim QC in Pakistan: Shade, Wash and Measurement

Denim shade is read after the wash, under a fixed light

Denim is a warp-faced twill. The warp carries the indigo and the weft stays undyed, and that construction gives denim a different defect profile from a plain dyed fabric.

Indigo penetrates the yarn only partly. Untwist a dyed yarn and the inner layers stay colourless: the colour sits as a ring at the surface, and that ring keeps fading and scratching with wear. Denim shade can't be read the way a piece-dyed shade is read, because the ring responds to every step after dyeing, from the indigo dyeing range through desizing, enzymes, bleach and abrasion to the last rinse in the laundry.

The wash creates the shade the consumer sees. A greige reading does not predict it, so shade is assessed after the actual wash, and under a fixed light source, because matched shades separate under a different lamp. Industrial colour work holds a standard D65 light source, and change in colour is scored against the grey scale for assessing change in colour.

Each defect starts at one stage and becomes unfixable at a later one

Leg twist, shrinkage and measurement drift are cheaper to catch before cutting than after the wash.

A denim production programme tracks weight, shade, shrinkage and wash performance together, because one reading proves one roll, not a lot.

Shade bands are sorted on the cutting floor, and labels keep them traceable to the wash

A large order uses hundreds of rolls from one dye lot, and rolls that differ in depth leave the mill as a shade range. Factories group cut parts by shade band and wash each band separately. The buyer may approve only three or four bands out of ten or twelve. The shade banding and shade sorting methods used on the cutting floor keep one carton to one shade.

Labels keep cut parts traceable from the cutting table to the wash drum. Without them, the laundry sorts by eye under whatever light the floor has, and mistakes there cause mass re-washing. The fix is a shade register with roll number, dye lot and inspection date.

Two laundries rarely match, so each proves its first bulk wash against a signed standard

Machine type, load weight, water hardness, enzyme time and bleach concentration all move the shade, even when two laundries run the same recipe, and the second wash stage separates them again.

The control is one approved wash standard per style, held physically and signed by both sides. Each laundry proves its first bulk wash against it before the order runs, because a laundry that fails a trial load fails on fifty thousand pieces.

Colour fastness testing does not replace that trial. Colour fastness to domestic and commercial laundering measures how a fabric behaves under a defined wash condition, which must match the care label. The recognised tests also cover rubbing and artificial light. Deeply dyed denim with weak fixation generates wet rubbing complaints, and the wet rub is the condition a damp, dark garment meets in wear.

Leg twist and shrinkage come from the fabric, measurement drift from cutting and sewing

Leg twist, also called skew or spirality, is the rotation of a garment's leg after washing. It comes from the fabric, not the sewing. ISO 16322-2 specifies procedures for determining spirality after laundering, and ASTM D3882 covers bow and skew in woven and knitted fabric. Both test the fabric, not the finished pair.

For shrinkage, ISO 6330 sets the washing and drying procedures and ISO 3759 governs specimen preparation and measurement. Together they underpin the test methods a buyer should write into the order.

Commercial programmes commonly allow about 3 to 5 percent shrinkage either way. Latent shrinkage is the risk: cotton that was never mechanically pre-shrunk can contract past that allowance. Pakistani mills differ in whether they apply a Sanforization step, so a pattern cut without accounting for five percent length shrinkage produces a garment five percent short after the first home wash.

Measurement drift is visible in-process. Three pieces per size at the 30 to 60 percent mark show a size curve that has moved before the cartons are sealed.

Whisker placement is checked against the approved sample, hardware by pull checks

Dry processes create the worn look: whiskering, hand sanding and scraping, then the wet stages. Whiskering and hand scraping are applied by hand on many lines, so placement varies with the operator, and the approved sample is the only reference for whisker position and abrasion depth.

A rivet that pulls through, a button that shears or a zip that sticks is an attachment problem. It shows up in an in-line pull check and at final inspection, and one critical attachment failure fails a lot.

AQL counts defects, but shade, whiskering and leg twist are judged against a reference

Pre-shipment inspection for denim works as it does for other apparel. A sample is drawn from packed cartons against a published sampling table, each piece is judged against an agreed defect list, and the lot passes or fails on the count. Tti Labs applies C:0 for critical defects, Mj:2.5 for major and Mi:4.0 for minor at general inspection level II.

AQL handles countable findings: a broken zip, a missing rivet, a measurement outside tolerance. Shade produces a judgment, so it sits outside the count. It is the defect that final inspection catches last and fixes least.

Fabric is graded separately. ASTM D5430 four-point grading charges penalty points by defect length, and shade is checked at grade 4 and above on the grey scale. The AQL sampling method that drives the garment count does not absorb the fabric grade.

The laundry's ZDHC record is a second file beside the quality data

Input chemistry is checked against the ZDHC Manufacturing Restricted Substances List, and discharge against the ZDHC wastewater guidelines. That record is no substitute for the shade and performance data, so ask a denim supplier for both files.

Tti Labs tests and inspects denim in the same accredited system as other softlines

• Fabric and garment testing under ISO/IEC 17025 accreditation, with the scope in PNAC accreditation LAB-022.

• Colour fastness, dimensional stability and wash durability through analytical testing services, plus fabric performance testing as a programme.

• Softlines inspection covering yarn, fabric and denim through inspection and audit services, inside an eight-stage cycle ending in loading supervision.

• AQL sampling with ASTM D5430 four-point grading, and shade assessed against the approved reference.

• ZDHC MRSL v3.1 approved certifier at Level 1 and Level 2, and ZDHC approved wastewater laboratory status.

• Coverage from Lahore, Karachi, Faisalabad and Sialkot, through the textiles and apparel division.

Tti Labs inspects and reports. It does not rework goods, coach lines to pass, or soften a finding for the factory.

Book denim testing and inspection with Tti Labs. UAN 111 786 001. Test the fabric, inspect the wash, grade the shade.

Related guides: REACH Testing for Pakistan Textiles, Leather and Footwear.