Dyeing Workshops and Lot Shade Control

Shade Is the Complaint That Never Goes Away

Shade variation is the most common reason a zipper is rejected at the garment line, and the most expensive to fix, because by the time the mismatch is visible the tape has already been assembled, plated, packed and shipped. Unlike a broken slider, shade cannot be repaired. It can only be prevented or sorted.

A dyeing audit therefore has two objectives. The first is to establish whether the workshop can reproduce a colour. The second is to establish whether it can keep different colours apart once it has produced them. Factories often pass the first test and fail the second.

Define the Lot Before Judging It

Ask the factory what a dye lot is. The answer tells you whether shade control is possible at all.

Is a lot defined by one dye vessel load, one production day, or one customer order?
Can two vessels produce the same lot number, and if so how is the difference recorded?
How many kilos is a typical lot, and how does that compare with the order quantity?
What happens when an order exceeds one lot: is it split, sorted, or blended?
Are lots numbered before or after dyeing, and by whom?

A factory that dyes in small lots and numbers them at the vessel has the foundation of control. A factory that numbers lots at packing has a labelling system, not a shade system.

Lab Dip and Approval

The lab dip is the contract for colour. Ask to see the approved dip for a colour currently in production, and ask how the dip is stored and re-used.

Approval record with the customer's signature or reference, and the date.
Storage conditions for approved dips: dark, sealed, at controlled humidity.
How long an approval remains valid, and whether it is tied to a dye class or a substrate.
Number of dip rounds before approval, as an indicator of process capability.
Whether the production recipe is derived from the dip recipe, and who converts it.

Recipe, Water and Chemicals

Dyeing is a chemistry process disguised as a wet process. The audit should test whether the inputs are controlled.

Recipe sheet per lot, with dye weights, auxiliaries, pH target and liquor ratio.
Weighing method: calibrated scale, dedicated dye kitchen, and a second-person check for critical colours.
Water source and hardness, tested and recorded; hardness variation is a common cause of shade drift.
pH measurement at the start and end of the cycle, with the instrument identified.
Chemical lot tracking, so a change of auxiliary supplier can be linked to a shade shift.

A passing answer includes a scale calibration sticker, a water hardness record and a recipe signed by the dyer. A common failure is a recipe that exists in a computer while the actual addition is written on the vessel in chalk.

Machine Control and Loading

Ask how the workshop decides load size, and what happens when an order is too small for a full vessel.

Vessel capacity and the minimum load that still gives level dyeing.
Liquor ratio control and whether it is calculated per load.
Temperature ramp rate and hold time, recorded by the controller or by hand.
Whether the controller programme is locked against operator changes.
How a partial load is compensated, and whether it is recorded as a separate lot.

Measurement: Eyes, Light Box and Spectrophotometer

Visual assessment under a defined light source is acceptable. Visual assessment under whatever light happens to be overhead is not.

Light box availability, with the standard illuminants used and the last lamp replacement date.
Viewing procedure: background, angle, observer, and whether metamerism is checked under two illuminants.
Spectrophotometer model, calibration status, and whether it is used for pass or fail decisions.
Colour difference limits stated numerically, with the tolerance method identified.
Who has authority to approve a borderline shade, and whether that approval is recorded.

Segregation and Shade Sorting

Physical separation of lots in the warehouse, with clear lot labels on every roll.
Shade sorting into numbered shade bands when a lot spans a range.
Rule for mixing bands within an order, and whether the customer has agreed it.
Packing instruction that prevents two lots in one polybag or one carton.
Records that allow a shipped carton to be traced back to a lot and a vessel.

Walk the finished goods area and look for a shelf where two lot numbers sit side by side without a divider. That is the finding.

Rework and Re-Dyeing

Ask how often lots are re-dyed, and what happens to the shade after a second cycle. Re-dyeing changes the physical properties of the tape and often moves the shade in a direction that is harder to correct.

Re-dye rate per month, and the top three causes.
Whether re-dyed lots are marked and whether the customer is informed.
Limit on the number of re-dye cycles per lot.
Whether re-dyeing is recorded against the original lot number or given a new one.

The Actionable Audit Checklist

A dye lot is defined by vessel load and recorded at the vessel, not at packing.
Approved lab dips exist for every colour in production and are stored correctly.
Recipes record dye weights, auxiliaries, pH and liquor ratio per lot.
The dye kitchen scale carries a valid calibration sticker.
Water hardness is tested and recorded on a defined frequency.
Vessel controllers are locked and programmes are not edited by operators.
Partial loads are compensated or recorded as separate lots.
Shade assessment uses a light box with a documented procedure.
Colour difference limits are numeric, not verbal.
Lots are physically separated in the warehouse with labelled rolls.
Packing rules prevent mixing lots in one carton.
Re-dye rate is tracked with causes and a cycle limit.

What a Passing Answer Looks Like

Passing sounds like this: "This order needed one thousand two hundred kilos, we ran three lots of four hundred, sorted them into two shade bands, and the packing list shows band one in cartons one to fourteen and band two after that." That answer shows the factory understands that shade control ends at the carton, not at the vessel.

YCC asks for that packing-level answer whenever a colour is critical, because a shade system that stops at the dye house door is only half a system.