Lab Dips and Shade Approval, Explained

What a lab dip actually is

A lab dip is a small piece of your fabric, dyed at laboratory scale to a trial recipe, submitted so you can judge the colour before a full lot is committed. The important detail is that it is dyed on the same fabric the order will run on, not on a generic cloth, because the same dye recipe reads differently on different constructions and blends.

This matters most in poly-viscose and poly-cotton fabrics, where the polyester and the viscose or cotton components take up dye differently. A shade that looks correct on one blend ratio will not necessarily land in the same place on another, so the lab dip is tied to the exact fabric quality it was dyed on.

From colour reference to recipe

The process starts with whatever reference you can provide, and the quality of that reference sets a ceiling on how tightly the match can be held. A physical swatch of the actual target is the strongest starting point. A colour system reference is workable. A printed image or a screen colour is the weakest, because both are reproductions in a different medium and neither carries the information a dyer needs.

From the reference, the dyehouse builds a recipe: which dyes, in what proportion, at what process conditions. Colour measurement equipment gives a starting point, but a recipe for a specific blend and construction is arrived at by trial, which is why more than one submission is normal rather than a sign of a problem.

• A physical fabric swatch of the target shade, ideally unworn and unwashed
• A recognised colour system reference, quoted with the exact code
• An existing garment, where nothing else exists, understanding that wear and washing have already shifted it
• The light source the uniform will actually be seen under, if it is unusual

Assessing a submission: light, angle and metamerism

How a lab dip is assessed decides whether the approval is meaningful. Two shades that match under one light can differ clearly under another, an effect called metamerism, and it is a real property of dyes rather than a trick of perception. Assessing under a single uncontrolled light is the most common way a shade approval goes wrong.

Assessment therefore happens under defined light sources, commonly a daylight simulator, a store or office light and an incandescent source, so a match can be confirmed across more than one condition. If a uniform will be worn under one dominant light, say a hospital corridor or a hotel interior, the shade should be judged under that condition too and the decision recorded.

• Assess under more than one light source, not just whatever light is in the room
• Lay the submission edge to edge with the standard, with no gap between them
• View both at the same angle, since fabric surfaces reflect differently when tilted
• Check both sides of the fabric, and both directions of the weave, on a textured or twill construction
• Record which light source the decision was made under, so a reorder can be judged the same way

Visual assessment and colour measurement

Two methods run in parallel. Visual assessment is a trained eye comparing submission to standard under controlled light. Instrumental assessment uses a spectrophotometer to give a numeric difference between the two, commonly reported as a single colour-difference value where a smaller number means a closer match.

Neither replaces the other. A numeric difference can sit inside a stated limit while a visual assessment still reads as off, particularly where the difference falls in a direction the eye is sensitive to. Where a program has a colour tolerance, it should be agreed in advance with the method that will be used to judge it, rather than invoked for the first time when a lot is being disputed.

From approved lab dip to bulk dye lot

Approval does not mean the recipe transfers unchanged to production. A laboratory dyeing and a full bulk lot differ in scale, machinery and process conditions, and the recipe is adjusted for bulk. This is why the first bulk lot is itself checked against the approved standard rather than assumed to match by virtue of the recipe.

For us, dyeing and finishing run through our partnered processing houses in Bhilwara while weaving happens in-house on our own looms at Village Atoon, so the fabric and the shade approval are scheduled together. A custom shade is woven and dyed to order from 500 m per shade, which is the quantity at which a dedicated dye lot makes sense; ready-stock shades already exist as running lots and start at 50 m.

Holding the standard for reorders

The approved submission becomes the shade standard, and it only does its job if it is kept properly. A standard stored loose in a drawer, exposed to light, or handled repeatedly will itself shift over months, and then every reorder is being matched against a moving target.

• Keep the approved swatch sealed and away from light, and keep a second copy
• Label it with the fabric quality, the shade name or code and the approval date
• Match every later lot against the standard, never against the most recent delivery
• Re-issue a fresh standard if the original has visibly aged, and record that you did

Matching each lot against the previous delivery rather than the original standard is how a program drifts. Each step looks acceptable, and after several lots the fabric no longer matches where it started. Our guide on dye-lot consistency covers that failure mode in more detail.

FAQ

Frequently asked questions

How many lab dip submissions are normal before approval?

More than one is routine. A recipe for a specific blend and construction is arrived at by trial, and a second or third submission usually reflects the shade being tightened rather than anything going wrong. Deep and highly saturated shades typically take more submissions than mid tones.

Can a shade be matched from a printed image or a screen colour?

It can be attempted, but it is the weakest possible reference and the match cannot be held tightly. Printing and screens both reproduce colour in a different medium, so neither carries the information a dyer needs. A physical swatch of the target, or a recognised colour system code, is worth the effort of obtaining.

Why does the same shade look different on two fabrics?

Because dye uptake depends on the fibre. In a poly-viscose or poly-cotton blend the components take dye differently, and the construction and finish change how light reflects off the surface. A lab dip is therefore tied to the exact fabric quality it was dyed on.

What is metamerism?

Two samples matching under one light source but not under another. It is a genuine property of the dyes involved, not an error in assessment, and it is the reason shade approval is done under more than one defined light rather than under whatever light happens to be available.

Does the approved lab dip guarantee the bulk lot will match?

It sets the target the bulk lot is measured against. Because laboratory and bulk dyeing differ in scale and machinery, the recipe is adjusted for production and the first bulk lot is checked against the approved standard rather than assumed to match.