Same Dye, Same Recipe… So Why a Different Colour?

The Hidden Impact of the Substrate Factor in Colour Formulation

When preparing a colour recipe, attention is often focused entirely on the target colour. The customer’s sample is measured, its colour coordinates are analysed, suitable dyes are selected, and the colour-matching software is expected to generate a recipe.

However, an accurate colour formulation does not begin solely with the question, “Which colour are we trying to achieve?” There is another question that is just as important:

On which substrate will this colour be created?

A dye recipe does not exist in isolation. Dyes are not applied to a completely neutral, colourless and standard surface. Before dyeing, every fabric already has its own initial shade, whiteness level, degree of yellowness, brightness and spectral characteristics.

Therefore, even when the target colour, dyes and process conditions remain the same, a change in the substrate can also change the final result.

In short, successful colour matching begins not with measuring the target colour, but with correctly defining the substrate.

The substrate is not simply undyed fabric

In dyehouses, the substrate is often regarded as raw, pretreated or undyed fabric. From the perspective of colour measurement and formulation, however, the substrate is the material in its actual, process-ready state immediately before the dye recipe is applied.

Preparing the correct substrate therefore does not mean selecting any undyed fabric from stock and measuring it. The substrate must have undergone the same pretreatment processes that will be used in production, must be homogeneous and must accurately represent the production fabric.

Scouring, bleaching, washing, neutralisation, optical brightening and similar pretreatment processes can change the fabric’s initial colour and spectral reflectance. If the substrate used in the recipe calculation is measured before these processes, the software will base its calculation on a previous state of the fabric that will no longer represent the actual starting point of production dyeing.

Where necessary, the substrate should also be prepared through a blank process, in which the auxiliaries, temperature, time, pH and washing conditions of the actual dyeing process are applied without adding any dyes. This is important because the whiteness, yellowness and overall colour characteristics of the substrate can be affected not only by the dyes, but also by the chemicals and process conditions involved.

A correctly prepared substrate should:

• Have the same fibre composition and construction as the actual production fabric.

• Undergo the same pretreatment processes that will be applied in production.

• Be free from oil, dirt, stains and surface irregularities that could affect the measurement.

• Be conditioned under standard atmospheric conditions before measurement.

• Be measured using consistent fabric orientation, number of layers, measurement surface and instrument aperture.

• Not be taken from edges, creased areas or irregular sections that do not accurately represent the production batch.

In addition, the substrate used for recipe formulation should be as consistent as possible with the substrate on which the dye calibrations were created. Calibration data generated on a substrate with a different fibre type, pretreatment process or optical whiteness level may not produce the same result on the actual production substrate.

The human eye may not immediately detect some of these differences. A spectrophotometer, however, measures the spectral reflectance of the substrate across the wavelength range. This reveals how differently two substrates that both appear “white” can actually behave.

If this difference is not correctly included in the recipe calculation, the software may calculate the effect of the dyes from the wrong starting point. As a result, even if the laboratory recipe appears theoretically correct, the target colour may not be achieved in the first dyeing.

Why can the same recipe produce a different colour?

Consider a pale beige shade that will be applied to three different substrates.

The first substrate is slightly yellowish, the second is neutral white, and the third is a bluish white containing an optical brightener.

If the same dye combination and concentrations are applied to all three substrates, the resulting colours will be different. The yellowish substrate may make the target shade appear warmer, while the optically brightened substrate may make it appear cooler and brighter. A recipe that produces the correct result on the neutral substrate may fall outside the target on the other two.

This effect is especially noticeable in light and pastel shades. At low dye concentrations, the original colour of the substrate makes a greater contribution to the final appearance. In darker shades, the dye may significantly reduce the visible influence of the substrate, but it would still be incorrect to assume that the substrate becomes entirely irrelevant.

Therefore, the answer to the question, “This recipe worked last month, so why does it not work today?” should not always be sought in the dyes, the operator or the machine.

Sometimes, the only variable that has changed is the substrate.

The substrate factor is the starting condition of the calculation

In colour-matching systems, the substrate factor—or SF approach—essentially allows the initial optical and colour characteristics of the material to be included in the recipe calculation. Although the way SF is calculated and applied may vary between systems, the fundamental objective remains the same:

To predict the colour that the dyes will create on the actual production substrate.

Colour-matching software cannot determine the correct recipe merely by evaluating the L*, a* and b* values of the target colour. It must consider the spectral behaviour of the dyes at different concentrations, the dyeing method being used and the initial reflectance of the substrate together.

The measured final colour is not produced by the dyes alone. It is the result of the interaction between the optical characteristics of the substrate and the way the dyes absorb and reflect light.

If the substrate data is incomplete or incorrect, the starting condition of the mathematical model will also be incorrect. Even the most precise calculation based on the wrong starting point may fail to produce the expected result in production.

Why are substrates containing optical brighteners more critical?

Fabrics containing optical brighteners are among the cases in which substrate management requires the greatest attention.

Optical brighteners can absorb ultraviolet energy and re-emit it within the visible spectrum, particularly in the blue wavelength region. This can make the fabric appear whiter, brighter and cooler. However, this appearance can change depending on the amount of UV energy present in the light source.

A recipe prepared on an optically brightened substrate may appear correct under D65 but look different under retail lighting, LED illumination or another standard light source. For this reason, evaluating colour harmony under only one light source is not sufficient when working with optically brightened substrates.

The UV characteristics of the substrate, the measurement conditions and whether the target sample contains optical brighteners must be evaluated together. Otherwise, a colour that appears numerically acceptable may fail visually under actual conditions of use.

Are the laboratory and production substrates genuinely the same?

One of the key causes of colour variation is the assumption that the substrate used in the laboratory has the same characteristics as the fabric entering production.

The laboratory substrate may have come from a different pretreatment batch. The whiteness of the production fabric may have changed, or the desizing and bleaching processes may have been carried out differently. There may also be small differences in fibre composition, fabric weight or surface structure.

If these differences are not recorded and the recipe is prepared using an earlier substrate, the discrepancy between the laboratory and production is already present before dyeing even begins.

A well-managed colour process therefore archives more than dye recipes alone. It also links each recipe to the substrate on which it was created, the substrate’s measurement data, the dye set used and the relevant process conditions.

The true value of a recipe lies not only in the quantity of each dye it contains, but also in knowing the exact conditions under which it produced the correct result.

How should the substrate be managed correctly?

For a reliable colour formulation, the actual substrate to be used in production must first be measured with a spectrophotometer under appropriate measurement conditions. Variables such as the number of fabric layers, orientation, measurement surface and instrument aperture must be standardised.

The substrates should then be classified according to information such as fibre type, fabric structure, pretreatment process, whiteness level and optical brightener status.

When preparing a new recipe, the substrate record closest to the actual production material should be selected instead of using any previously measured white substrate. If there is a significant change in the production substrate, the old recipe should not be applied directly. It should be recalculated or corrected using the new substrate data.

Establishing a standard procedure for substrate measurement offers a major advantage, particularly for frequently repeated colours. A previously successful recipe can then be reused not only by referring to its colour name, but together with the substrate and process information that made it successful.

Not more dye, but more accurate data

Failure to achieve the target colour in the first dyeing does not result only in additional dye and correction costs. It can also require new laboratory samples, extend