What is a lab-dip and why is the approval process a starting point?
Lab-dip (laboratory dip dyeing) is a dyed sample prepared at laboratory scale to reach a reference colour supplied by the customer (a Pantone, a physical fabric, a lab standard or a digital value). The aim is to verify the recipe, the dyestuff combination and the process parameters before going into production. Several variants are usually prepared for the same target, because even when different dyestuff trichromies produce the same shade, they can behave differently under different light (see metamerism).
An approved lab-dip is not merely "a nice colour" but a measurable standard. This standard is used as the reference in all subsequent stages (bulk dyeing, batch repeats, shipment control). For the details of colour-difference evaluation you can consult our colour difference and ΔE guide. This process is as closely linked to how the dye fixes onto the fabric as it is to the fixation and finishing steps.
How is colour difference evaluated with ΔE, and what does ΔE<1 mean?
Colour difference is based on a measurable number rather than the observer's subjective judgement. Delta E (ΔE) measures the difference between the standard and the batch in the CIELAB space (L* lightness, a* red-green, b* yellow-blue). As a general rule, the larger the ΔE value, the greater the visible difference; at very low values the difference becomes practically imperceptible. Our target is to stay within the ΔE<1 band against the approved standard, although the acceptance threshold is finalised according to the customer tolerance and the colour.
An important point: although ΔE is a single number, which formula it is calculated with changes the result. Classic CIELAB (ΔE*ab) and the perceptually more consistent CMC or CIEDE2000 can produce different values. For this reason, when a tolerance is defined, not only the number but also the formula must be agreed.
| ΔE band (approx.) | Perceptual interpretation | Practical meaning in production |
|---|---|---|
| ΔE < 1 | Very difficult to distinguish even with a trained eye | Generally accepted as safe; our target band |
| 1 ≤ ΔE < 2 | Perceptible in side-by-side comparison | Evaluated according to the colour and customer tolerance |
| 2 ≤ ΔE < 3.5 | Distinct difference | Considered out of tolerance for most shipments |
| ΔE ≥ 3.5 | Clearly different shade | Requires recipe/process correction |
The bands above are indicative and not absolute; for example, in dark or highly chromatic colours the eye perceives the difference differently compared with light colours. For this reason let us define the acceptance threshold together for each project.
How do light source and metamerism affect colour approval?
How a colour appears depends on the spectral content of the light falling on it. Two samples may look identical under one light source and differ under another; this phenomenon is called metamerism and arises from different dyestuff combinations producing the same shade. For this reason a lab-dip is not evaluated under a single light.
A standardised light cabinet is used during approval, and the sample is compared under the agreed light sources. One of the common reference illuminants is the D65 (approximately 6500 K, average daylight) standard illuminant; alongside this, sources such as incandescent/store lighting (e.g. A) and fluorescent (e.g. TL84/CWF) are used. The aim is for the colour to remain close to the standard under all these sources — that is, for the metameric shift to be small.
| Light source (illuminant) | Approximate character | Role in approval |
|---|---|---|
| D65 | Average daylight, ~6500 K | Primary reference illuminant |
| A (incandescent / store) | Warm, yellowish, ~2856 K | Store environment simulation |
| TL84 / CWF (fluorescent) | Store fluorescent | Metamerism control |
| UV component | Triggers optical brighteners | Evaluation of white/light shades |
Spectrophotometer measurement supports the subjective eye assessment: by measuring the spectral reflectance of the sample, the instrument gives the calculated ΔE value for each illuminant. In this way both numerical and visual approval are documented together.
What is the difference between the CMC and CIEDE2000 formulae?
Classic CIELAB ΔE*ab gives the straight geometric (Euclidean) distance between two points. The problem is that our eye is not equally sensitive to differences in lightness, chroma and hue; for this reason the same ΔE*ab value can be "visible" in one region of the colour space and "invisible" in another. The CMC (Color Measurement Committee) formula introduces weightings for lightness (l) and chroma (c); in textiles CMC(2:1) is frequently used. CIEDE2000 further improves perceptual consistency by adding corrections such as lightness, chroma and hue weightings together with hue-chroma interaction.
| Formula | Key feature | Practical use |
|---|---|---|
| CIELAB ΔE*ab | Simple Euclidean difference, unweighted | Quick, basic comparison |
| CMC(l:c) | Lightness/chroma-weighted elliptical tolerances | Common in textiles; CMC(2:1) frequent |
| CIEDE2000 (ΔE00) | Lightness/chroma/hue + interaction corrections | Most perceptually consistent; modern standard |
In practice, what is critical is that the same formula and the same tolerance are agreed at the outset for the standard and the batch. Whether the expression ΔE<1 is defined according to CIELAB or to DE2000 directly affects the accept/reject outcome. For this reason, at the start of approval the formula, illuminant set and tolerance are put in writing together.
How is the approved colour carried into bulk production without shifting?
A recipe that "holds" at lab scale does not automatically give the same result at production scale. The liquor ratio, the heating/cooling curve, the mechanical action and the machine geometry differ from the laboratory. For this reason a scale-up bridge is established between the approved lab-dip and bulk production: the recipe is adapted to the production machine, the first bulk batch (bulk-up) is dyed and measured against the approved standard.
The main practices that safeguard colour continuity:
- Standard fixing: The approved lab-dip is archived digitally (spectral data) and, where possible, physically; all batches are measured against this single standard.
- Recipe scaling: Dyestuffs and auxiliary chemicals are recalculated according to the production liquor ratio.
- First-batch verification: The bulk-up batch is measured against the standard using the chosen formula (e.g. DE2000); if it does not fall within the ΔE band, a correction bath or a fine recipe adjustment is carried out.
- Within-batch and between-batch control: Within the same batch, head-middle-end and, across different batches, the shade are monitored to remain close to the same standard.
- Accounting for the finishing effect: Because finishing steps such as sanforising, compacting and stenter — part of finishing — can shift the shade slightly, approval is ideally confirmed on the post-finish shade.
Colour continuity is the result not only of the dyeing step but of the fabric's entire journey. We explain how a single coordinated flow — in-house knitting plus a vetted contract network for dyeing and finishing — makes this easier on our coordinated contract network advantage page. For the effect of dyeing methods on colour, you can look at our reactive and disperse dyeing comparison.
What are the steps of the lab-dip approval flow?
The table below summarises a typical lab-dip approval flow in terms of step, the output produced and the control criterion at that step. The exact order and number of steps are finalised according to the project.
| Step | Output | Control criterion |
|---|---|---|
| 1. Target definition | Reference colour (physical fabric / Pantone / spectral data) | Illuminant set, formula and tolerance put in writing |
| 2. Lab-dip preparation | Several recipe variants (samples) | Metamerism option via different dyestuff trichromies |
| 3. Evaluation | Light cabinet + spectrophotometer measurement | ΔE against the standard; metamerism under multiple illuminants |
| 4. Approval and standard fixing | Approved lab-dip = reference standard | Spectral + physical archive; locking to a single standard |
| 5. Recipe scaling | Recipe adapted to the production machine | Correction of liquor ratio, temperature curve and time |
| 6. Bulk-up verification | First bulk batch | ΔE<1 target against the standard; post-finish confirmation |
| 7. Series production control | Subsequent batches | Within-batch/between-batch shade consistency monitoring |
This flow runs together with colourfastness tests: as much as the approved shade matters, so does that shade's durability against washing, rubbing and light. The ISO/AATCC fastness tests for the fastness side, and again our colourfastness and ΔE guide for rubbing/crocking evaluation, are complementary.
Common tolerance questions in the approval process
The tolerance band is not a fixed universal value; it is set according to the colour, the fabric structure and the end use. The eye tolerance of a dark navy single jersey and a pastel interlock may not be the same. Likewise, while the UV component is decisive in light shades containing optical brighteners, in dark shades the chroma direction comes to the fore. For this reason, instead of a single "let ΔE be this for everything" rule, a project-specific agreement is preferred.
Practical recommendation: at the start of approval, put three things in writing — (1) the acceptance formula (e.g. CIEDE2000), (2) the illuminant set (e.g. D65 + A + TL84) and (3) the numerical tolerance (e.g. ΔE<1 target, upper limit subject to customer approval). These three decisions ensure that both the laboratory and production work towards the same target and minimise disputes that may arise later. For any threshold that remains uncertain, rather than inventing a specific value, let us define it together.
Frequently asked questions
What is a lab dip, and why is it the starting point of the color approval process?
A lab dip is a dyed sample prepared at laboratory scale to match the reference color the customer has supplied (Pantone, a physical fabric, a lab standard or a digital value). Its purpose is to validate the recipe, the colorant combination and the process parameters before moving into production. An approved lab dip is not merely an attractive shade but a measurable standard; in bulk dyeing, batch repeats and shipment control it is measured numerically against this reference.
What does ΔE<1 mean, and which ΔE band is acceptable?
ΔE is the numerical measure of the difference between standard and batch in CIELAB space (L*, a*, b*); the closer it is to zero, the closer the colors are to each other. ΔE<1 is our safely accepted target band, very hard to distinguish even by a trained eye. 1≤ΔE<2 is judged according to the color and the customer tolerance; 2≤ΔE<3.5 is out of tolerance for most shipments; ΔE≥3.5 calls for a recipe or process correction.
Why is color approval not done under a single light source, and what is metamerism?
The appearance of a color depends on the spectral content of the light striking it; two samples may look identical under one light yet differ under another source. This phenomenon is metamerism, and it arises when different colorant combinations produce the same shade. For this reason approval is carried out in a standard light booth under several agreed sources: D65 (~6500 K daylight) as the primary reference, with A (incandescent/store) and TL84/CWF fluorescent used to check for metamerism.
What is the difference between the CIELAB, CMC and CIEDE2000 formulas?
The classic CIELAB ΔE*ab gives the unweighted Euclidean distance between two points; however, the eye is not equally sensitive to differences in lightness, chroma and hue. The CMC formula introduces weightings for lightness (l) and chroma (c); CMC(2:1) is widely used in textiles. CIEDE2000, with its lightness, chroma and hue weightings plus a hue-chroma interaction correction, is the modern standard that is perceptually most consistent. Because the same ΔE value can vary by formula, the formula must also be agreed at approval.
How is an approved color carried over into bulk production?
A recipe that holds at lab scale does not automatically give the same result at production scale; the liquor ratio, heating/cooling curve, mechanical action and machine geometry all differ. For this reason the approved lab dip is archived both digitally and physically and locked as the single standard, the recipe is recalculated for the production liquor ratio, the first bulk batch (bulk-up) is measured against the standard, and within-batch and batch-to-batch shade consistency is monitored. Since sanforizing, compacting and the stenter can shift the shade, approval is ideally done after finishing.
Why should the color tolerance be put in writing from the outset for every project?
The tolerance band is not a universal fixed value; it is set according to the color, the fabric construction and the end use. The visual tolerance of a dark navy single jersey and a pastel interlock may not be the same. For this reason three things are put in writing at the start of approval: the acceptance formula (e.g. CIEDE2000), the illuminant set (e.g. D65 + A + TL84) and the numerical tolerance (e.g. ΔE<1 target). This way the laboratory and production work to the same target, and accept/reject disputes in bulk production are minimized.