Achieving Textile Colour Accuracy: What Actually Works in Real Life

Digital textile printing offers enormous design freedom and a wide range of materials. However, colour control is significantly more challenging than with smooth, paper-like media. Fabrics stretch, fray and curl at the edges, and often have different optical properties to paper. To achieve reliable, repeatable colour results, the measurement process must therefore be tailored specifically to the textiles used.

Today, virtually every print job starts with a digital file. This is processed via a RIP with colour profiles according to the ICC standard, and then sent to the printing press for output. However, the colour profile is only as good as the spectral data on which it is based. Therefore, a spectrophotometer is the most important tool for creating robust printer and media profiles rather than relying on a visual check or camera.

In the printing industry, the international standard ISO 13655 is the central guideline for colour measurement. It specifies how measurements must be taken to ensure colours are reproducible, comparable and of consistent quality, regardless of where or on which device they are printed.

Measurement geometry
A measurement geometry is defined to ensure that a measuring device captures and reproduces light at the correct angles. For printed products, the standard angles are 45°/0° or 0°/45°. This prevents gloss or texture from distorting the result.

Measuring conditions (M0–M3):
These abbreviations represent the various lighting conditions in which the measurements were taken. This may sound technical, but it is important.

• M0: standard light with uncontrolled UV content.
  The light source is usually a halogen lamp where the UV component is not precisely regulated. Many older measuring devices work with M0. Disadvantage: OBAs (optical brightening agents) can 'glow' to varying degrees depending on the device, leading to non-comparable results.
  
  
• M1: daylight-like with a defined UV component (recommended for OBAs).
  It simulates standardised daylight (D50), as used in standard-compliant light booths. Advantages: Measurements of materials with optical brighteners are more realistic and correspond better to the visual impression.
  
  
• M2: UV component filtered out.
  This uses a light source without a UV component. This completely suppresses fluorescent effects, such as those caused by OBAs. This measurement condition is used when UV-induced brightening is not to be taken into account, for example in a scientific evaluation.
  
  
• M3: Polarised measurement:
  Uses M2 plus a polarising filter to reduce reflections on shiny or textured surfaces. It is ideal for technical fabrics, silk matt fabrics and fabrics with a strong sheen.

Surface for measurement
To prevent distortion of the colour by the material (e.g. thin or transparent fabrics), measurements should always be taken on a defined white or black surface. Using an improvised surface, such as a desk or piece of cardboard, can lead to completely different values.

In short, adhering to the requirements of ISO 13655 ensures that colour measurements are consistent and comparable, regardless of the person conducting the measurement or the device used.

1. Textured surfaces
   Yarns, stitches and fabrics create microstructures with shadows and indentations. If the measuring aperture is too narrow, it will only capture a small area, meaning local deviations will disproportionately influence the measurement result. For structured or low-resolution fabrics, a larger aperture (6–8 mm) produces a more stable and representative result.
   
   
2. Distorted or uneven measurement fields
   Even when fixed carefully, fabrics often do not lie completely flat. Devices with image-based patch recognition can compensate for this by automatically positioning the measurement correctly. In other words, they measure where the patch actually is, rather than where it should be according to the template. Some systems on the market already work successfully according to this principle.
   
   
3. Fixation and backing
   Specialised textile sample holders, such as electrostatic frames and adhesive mats, keep even thin or elastic materials flat and stable. They also ensure that the backing meets ISO standard requirements. For highly translucent fabrics, a white backing or a multi-layered sample prevents distorted measurements caused by light shining through.
   
   
4. Fibres in the measuring optics
   Textiles shed fibres, and loose fibres in the area of the measuring aperture can distort the results. This is particularly the case when fibres from different fabrics accumulate over time. Devices specially developed for use with textiles often have an air purge function to keep the optics clean. However, even these devices – and devices without this function in particular – should be cleaned regularly.
   
   
5. Optical brighteners and the influence of light
   Many textiles contain optical brighteners. If the appropriate UV components are not taken into account during measurement, the results will differ from the visual impression. If fluorescence is a factor, measurements should be taken using M1 in accordance with ISO 13655, as this simulates a D50 light source. M2 is only useful if UV components are to be deliberately excluded. M3 can help to minimise reflections on heavily structured or silk-matt technical fabrics.

After measurement, the ΔE value indicates the degree of colour difference between two samples. A ΔE value between 1 and 2.5 is considered the threshold for visible differences. In practice, the following guidelines apply:

• ΔE < 1: difference not perceptible
• ΔE 1–2: only visible when compared directly (suitable for high-quality products).
• ΔE 2–3.5: Visible, but often still acceptable (standard range for textile printing).
• ΔE > 3.5: Clearly visible and usually unacceptable.

Acceptable tolerances vary considerably depending on the application (e.g. fashion, technical textiles, advertising banners).

The result is influenced by more than just the materials used. The type of ink used also has a significant impact on the colour impression. Not all inks behave in the same way, which is particularly important in textile printing. Depending on the type of ink used, the same motif can appear very different on the same fabric.

There are various types of ink used in textile printing. The following are among the most commonly used:

Pigment ink: This adheres to the surface of the fabric and is therefore well suited to simple applications, although it sometimes has a limited colour spectrum.

Reactive ink: This ink reacts chemically with the fibre and is often used for cotton. It produces brilliant colours, but requires post-treatment.

Dispersion or sublimation ink: This is particularly suitable for polyester fabrics as it 'soaks into' the material, producing vibrant colours that are highly durable.

The number of colours used in the printing system also influences the colour space, i.e. the range of colours that your printing machine can reproduce. For example, 4-, 6- or 8-colour inks may include additional colours such as orange, blue or green.

Colour management does not end with printing. The durability of colours in terms of wash fastness, rub fastness and light fastness is tested by separate ISO standards. Colour durability depends heavily on the ink used and post-treatment: reactive inks are highly wash-resistant when correctly fixed, whereas pigment inks can be damaged if washed without fixing.

Even when two printing systems are fed with the same file, the results can look completely different because the inks react differently.

The only way to reliably predict colour effects and gamuts is to print, measure and compare. However, this must be done for the exact materials, inks and machine configuration used.

To achieve repeatable results, ICC profiles are created. These ensure that images are correctly translated into the 'colour space' of the respective printing environment in terms of colour. This is also why the International Colour Consortium (ICC) recommends profiling each printing process individually.

Nevertheless, not every colour in the design file can be reproduced by every printer. The 'rendering intent' specified in the ICC profile determines how these colours are processed to achieve the closest possible match to the original display.

Perceptual: Compresses all colours proportionally – ideal for photos.

Relative colourimetric: Only shifts colours outside the colour space – ideal for corporate colours.

Saturation: Maximises luminosity, making it ideal for graphics and charts.

However, be careful. Selecting the incorrect rendering intent may result in dull or distorted colours.

Measuring textiles is much more difficult than measuring paper. However, with the right knowledge and precautions, this is perfectly feasible. Adhering to ISO 13655 and using suitable measurement conditions, larger apertures and secure fabric fixation, as well as keeping the optics clean, will result in high-quality spectral data. This will result in colour profiles that the RIP can interpret correctly and impressive print results, even under production conditions. Therefore, if you want to print textiles professionally, you need well-thought-out colour management, not luck.