How Do You Keep Dye-Lot Colour Consistent Across Reorders?

Shade is the single most common reason a reorder is rejected, and the single most avoidable. It is avoidable not because dyeing can be made perfectly repeatable, but because the difference between two lots can be bounded and measured long before a carton is packed. What makes shade disputes painful is that they are usually conducted in words.

The fix has three parts. A physical reference panel from the approved run, stored away from light. A band, written before production, that says how far the reading may move. And a named light source and method, so the reading means the same thing to both sides. None of that requires a laboratory on site.

What Exactly Is a Dye Lot and How Big Is It?

A dye lot is the quantity of fabric dyed together in one bath, or continuously in one run without a recipe change. Its size is set by the dyehouse: it may be a few hundred metres for a small order or several thousand metres for a programme colour. Buyers rarely know the size, which is the first thing worth asking.

Lot size matters because it sets how often the shade can move. If a programme consumes three lots a year, the shade can move three times a year, and each move needs a comparison against the retained reference panel. If one lot covers the whole year, the risk is concentrated in a single booking decision instead.

Why Does the Same Recipe Give a Different Shade?

Six causes account for most lot-to-lot movement. Water quality differs between seasons and between treatment cycles. Dye strength varies by shipment, and a shipment is standardised to a tolerance rather than to an exact value. The liquor ratio shifts with load size and with how wet the fabric enters the bath.

Dwell time and temperature profile shift with the machine and with the operator. The substrate itself differs: two rolls of the same greige fabric can absorb differently if they came from different weaving lots. And the finishing step - coating, calendering, softening - changes the apparent shade again after dyeing is finished.

How Is a Shade Band Agreed Instead of Argued?

A shade band is a number agreed in writing before production, expressed as an instrumental colour difference against the retained reference under a named illuminant and observer angle, with a gray scale grade as the fallback when the two sides read it differently by eye. It is a commercial agreement, not a published limit.

Agreeing the band early changes behaviour at the dyehouse. When the target is a recipe name, the dyer matches to a code and the result is whatever the lot gives. When the target is a panel with a band, the dyer matches to the panel and adjusts the lot until the reading sits inside the band. Same machine, different target, different outcome.

Agreeing the band also means agreeing who measures and when. The reading that settles a dispute is the one taken at inspection, before the cartons are sealed, by a named grader using a named instrument against a named panel. A reading taken later, at the destination, by someone with a different panel under a different lamp, will not match the first one and should not be expected to.

What Does a Retained Reference Panel Do?

The reference panel is a cut piece of the approved finished fabric, sealed, dated and stored away from light, held by both parties from the same run. It is the physical answer to the question the reorder asks: not what does the recipe say, but what did the approved bag looked.

Two panels should be retained from the same run, one working and one archive. The working panel is used at the comparison station and slowly ages; the archive panel is opened only when the working panel is suspected of having faded. Comparing against a faded panel produces a false pass, which is worse than carrying out no comparison at all.

How Is Colour Read by Instrument and by Eye?

An instrument reading produces a colour difference number from a spectrophotometer or a colorimeter, and it is only meaningful when the illuminant, the observer angle and the reference are stated. The same two panels produce different numbers under different illuminants, which is not an error but a property of colour.

A visual reading uses a gray scale, which grades the perceived difference in steps rather than producing a number. It is slower and more subjective, but it is what a customer in a shop actually experiences, so it is worth keeping as the fallback. Use the instrument to settle the arithmetic and the gray scale to settle the argument.

What Is Metamerism and Why Does It Ruin Agreements?

Metamerism is the effect where two panels match under one light and differ under another, because their reflectance curves differ even where their apparent colour does not. It is the reason a shade can be accepted in a booth and rejected in a shop, and it is the single most common cause of a shade agreement collapsing later.

The defence is to compare under more than one named illuminant during approval, and to record which illuminants were used. A panel that matches under two or three sources is far less likely to produce a disagreement downstream than one that matches under a single lamp, however carefully.

Metamerism is also the reason a digital or printed colour reference cannot carry a programme on its own. A printed swatch has one reflectance curve; the approved fabric has another. They can match under the lamp in the office and separate under the lamp in the shop, which is exactly the disagreement a reference is supposed to prevent.

Where a programme cannot afford to compare under three sources, the minimum is two: one daylight-equivalent source and one store-lighting source. Record both on the dye-lot record. That single line converts a later disagreement from a matter of opinion into a question about whether both readings were taken, which has one answer.

How Many Units Should Be Checked for Shade?

Shade is judged per lot rather than per carton, so the sampling follows the standard attribute plan for the lot size and the units are then read against the panel. Under ISO 2859-1 at General Inspection Level II and AQL 2.5, a lot of 501 to 1,200 units takes a sample of 80, and a lot of 1,201 to 3,200 takes 125.

Within each unit, read the body panel at the same named position on every bag, because shade can vary across a panel as well as between panels. A single reading per unit at a fixed position is repeatable; a reading taken wherever looks convenient is not, and it is the reason two inspectors disagree about the same carton.

Shade should also be read across the run rather than only within the sample. A lot that is dyed continuously can drift from the start of the run to the end, so a sample pulled from the first cartons can pass while the last cartons sit outside the band. Reading one unit from the first, middle and last pallet catches that at almost no extra cost.

Where a run is packed into several containers, record which dye lots went into which container. A shade difference confined to one container is a very different commercial problem from the same difference spread evenly across a shipment, and only the mapping can tell the two apart.

What Happens When Two Panels on One Bag Differ?

A bag made from two fabric components - body and base, body and trim, body and lining - can show a difference between its own panels even when each panel matches its own reference. This is usually a greige or a dye-lot mismatch between two components that were approved together but bought separately.

The control is to approve components as a set, not individually, and to retain a reference for the assembled bag as well as for the fabric. Where a programme has several colourways, each colourway needs its own assembled reference, because a panel that matches in one colourway has no bearing on another.

How Does a Dyehouse Match to a Panel Rather Than a Code?

Matching to a panel means the dyer is given the physical reference, adjusts the recipe in small additions, and submits a lab dip for comparison under the named illuminants before the bulk lot is dyed. It costs a little more time than matching to a code and it is the single most effective control a programme can buy.

The lab dip should be retained and dated as well, because it is the record of what the bulk lot was intended to match. Where a dispute arises six months later, the chain is reference panel, lab dip, bulk lot - and a break in that chain is usually where the problem is found.

What Goes Into the Dye-Lot Record?

One record per lot: the lot number, the greige source, the dye shipments used, the machine, the load size, the profile, the lab dip reference, the instrumental reading against the panel, the illuminants used, the units covered, and the date. Ten fields, one sheet, kept with the spec file.

Lot number

Assigned by the dyehouse, cited on the fabric roll tag

Greige source

Weaving lot reference and supplier

Dye shipments

Batch codes for each dye in the recipe

Machine and load

Machine number and load size in metres or kilograms

Profile

Time and temperature profile actually run

Lab dip

Retained dip, dated, matched to the reference panel

Instrument reading

Colour difference and gray scale grade, illuminant named

Coverage

Which units of which run used this lot

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