Denim QC in Pakistan: Shade, Wash and Measurement

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. Indigo only partly penetrates the yarn, so the colour sits as a ring at the surface around an undyed core. That ring responds to every step after dyeing, from the indigo dyeing range through desizing, enzymes, bleach and abrasion to the last rinse.

So a greige reading does not predict the shade a consumer sees. Shade is judged on the washed garment, against the approved standard, in a light booth with a fixed source such as the D65 standard light, because two shades that match under one lamp can separate under another.

Change in colour is scored on the ISO 105-A02 grey scale: five steps, or nine with half steps, where grade 5 means no visible change. The pass grade is set in the buyer's specification, not in the scale.

Where each defect starts, and when it can no longer be fixed

Sort cut parts by shade band and keep the label to the wash

A large order uses many 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, so one carton holds 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 a wrong sort means rewashing. A shade register that records roll number, dye lot, shade band and inspection date makes the sort checkable.

Prove the first bulk wash against a signed standard

Machine type, load weight, water hardness, enzyme time and bleach concentration all move the shade, so two laundries running the same recipe rarely match. 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.

Colour fastness tests do not replace that trial. They measure how the fabric behaves under a defined condition: ISO 105-C06 for laundering, which should match the care label, ISO 105-X12 for dry and wet rubbing, and ISO 105-B02 for light. Wet rubbing matters most on dark denim, because a damp, deep shade is what transfers onto skin and upholstery.

Test shrinkage on the bulk fabric, then cut to the result

A shrinkage test has three parts. ISO 3759 sets how the specimen is marked and measured, ISO 6330 sets the washing and drying procedure, and ISO 5077 gives the method for calculating the dimensional change. Buyers selling in the US often specify AATCC TM135 for fabric and AATCC TM150 for garments instead.

The result is a percentage of the original length, reported separately for warp (length) and weft (width), with a minus sign for shrinkage. The acceptable figure comes from the buyer's specification. No standard sets one.

Worked example. A lab marks 50 cm in the warp and 50 cm in the weft. After washing and drying, the marks measure 47.5 cm and 49.0 cm, so the fabric shrinks 5.0 percent in length and 2.0 percent in width.

• A 32 in finished inseam is cut at 32 ÷ 0.95 = 33.7 in.

• A 16 in finished leg opening is cut at 16 ÷ 0.98 = 16.3 in.

• Cut at 32 in instead and the inseam finishes at about 30.4 in, more than an inch and a half short.

Rolls from different finishing lots can shrink differently, so the test belongs on bulk fabric from the lot being cut, not only on the development sample.

Leg twist comes from the fabric, not the sewing

Leg twist, also called skew or spirality, is the rotation of a garment leg after washing. The fabric carries it and washing releases it, so it can't be corrected on a finished pair. ASTM D3882 measures bow and skew in the fabric, ISO 16322-2 measures spirality in fabric after laundering, and ISO 16322-3 does the same on finished garments. AATCC TM179 is the US method for skew change after home laundering.

Which test proves which result

Every method in this table is on Tti Labs' ISO/IEC 17025 accreditation scope LAB-022.

A denim QC checklist, stage by stage

Before cutting

• Approved shade standard and approved wash standard, signed by buyer and factory

• Light booth source agreed, for example D65

• Fabric inspection report per roll, with a shade band register

• Bulk fabric tests: shrinkage warp and weft, skew, rubbing dry and wet

• Pattern adjusted to the measured shrinkage

During production

• Cut parts labelled by shade band through sewing and washing

• First bulk wash approved against the wash standard

• In-line measurement checks against the size chart

• Whisker and abrasion placement checked against the approved sample

• Rivet, button and zip pull checks

Before shipment

• Final inspection on packed cartons, with an AQL sample and agreed defect list

• Shade and leg twist judged on washed garments against the references

• Washed garment tests where the buyer requires them

• The laundry's ZDHC chemical and wastewater records filed beside the quality data

AQL counts defects; shade and whiskering are judged against a reference

Final inspection draws a sample from packed cartons against a published sampling table, judges each piece against an agreed defect list, and passes or fails the lot 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, unless the buyer specifies otherwise. The AQL sampling guide and the pre-shipment inspection guide show the sample sizes and pass limits.

AQL handles countable findings: a broken zip, a missing rivet, a measurement outside tolerance. Shade, whisker placement and leg twist are judgments against a reference, so they sit outside the count, and one critical attachment failure fails the lot.

Fabric is graded separately, roll by roll. ASTM D5430 gives the procedure for visually inspecting and grading fabric, and it is used for acceptance only when buyer and seller agree it. The penalty-point limit a roll must meet comes from the buyer's contract, not from the standard.

The laundry's ZDHC record is a second file

Input chemistry is checked against the ZDHC Manufacturing Restricted Substances List and discharge against the ZDHC Wastewater Guidelines. That record says nothing about shade or shrinkage, so ask a denim supplier for both files. The ZDHC wastewater guide for denim mills and laundries covers the chemical side.

How Tti Labs tests and inspects denim

• Fabric and garment testing under ISO/IEC 17025, scope PNAC LAB-022, through analytical testing services.

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

• AQL sampling with ASTM D5430 fabric grading, and shade judged against the approved reference.

• ZDHC MRSL V3.1 certification at Level 1 and Level 2, and ZDHC approved wastewater laboratory status, through sustainability services.

• Offices in 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.

Related guides: REACH Testing for Pakistan Textiles, Leather and Footwear, During Production Inspection (DUPRO).