How to measure the colour of Fabrics

How to measure the colour of Fabrics

Measuring the colour of fabrics

The different types of fabric, both natural and synthetic, are a broad spectrum of materials that have many different uses in many different industries. Each fabric has its own qualities and physical characteristics that make it adept at certain functions and uses. For fabrics used in the clothing and fashion industry, quality and consistency are extremely important factors to consider during production. Even if appearance is not as important to a manufacturer and worth is the main factor focused on during production, appearance can still be an indicator of the quality of the production process.

When to measure

• Finished Product
When we speak of measuring the colour of fabric, the main point at which to measure would be right at the end of production when no more changes are to be made to the material and it is ready to be shipped to a customer. This stage in the manufacturing process is the absolute final point that can prevent any sub-standard product being sent out and any complaints being received. This doesn’t mean that this is the only point that requires appearance analysis; there are multiple stages that could be markers for colour measurement to ensure a truly top quality product but a measurement at this point will provide useful data.

• Raw Material
The raw material right at the start of production can be analysed for suitability; there is little point in subjecting fibres to an entire production process if they are not of normal quality and appearance. The same principle applies for blended fabrics, any material being used in manufacturing, at any point, should be analysed for quality before use. Taking a colour measurement here could save a lot of time and money further on in production however, there are impurities to think of. Some fibres go through at least two cleaning processes before being processed into the relevant fabric so the decision lies with the manufacturer whether or not it is feasible to take measurements after cleaning as this is a more ideal stage.

• After Mixing Materials
When making some fabrics such as jackets or sportswear, fibres of one variety may be blended with fibres of another to get the desired physical characteristics and qualities required by a fabric of that nature. Blending the fibres can sometimes alter the appearance and is something that could be monitored.

• After Drying
Different fabrics have different drying methods and these different methods can have an effect on the end appearance. For example, wool can either be dried using a hot-air process or a cold-air process. Cold air is undoubtedly better for the wool but takes time and is more expensive. Hot-air drying processes are quicker and more effective however they can cause yellowing of the wool which then affects the final appearance and, if using dyes, could affect the amount of dye needed to get the desired colour of the finished product.

• After Dyeing
If a customer has requested a specific colour, for example a certain shade of indigo for jeans, then they will expect all products produced to be of the same colour from garment to garment over the period of time that they are stocking it. If some materials are being dyed with a slightly different colour than others then it will be noticeable and cause complaints and, possibly, the product to be returned.

• Dyes / Colorants
Before getting to the stage where the fabric has already been dyed, the dyes themselves can be analysed for quality. Dyeing a fabric resulting in the wrong hue can often lead to products being returned and unhappy customers. Making sure the dye used is of the correct quality and colour before use can prevent any wasted products or unsatisfactory final products.

Suitable Instrumentation

A spectrophotometer would be able to drastically increase the efficiency of any quality control processes already in place. Gauging colour quality by eye is a very subjective task that varies from person to person. Being able to provide numerical data to describe the colour can negate any errors made by human observation and allow for a detailed record of fabric appearance to be kept.

The type of spectrophotometer to use would depend on what materials there are to measure. If there was simply the fibres or the fabric to be measured then a reflectance instrument could be used. If liquid dyes need measurements, then an instrument would be needed that can do both reflectance and transmission colour measurements.

There are a variety of Hunterlab Spectrophotometers that are capable of taking the measurements needed. For reflectance measurements, the LabScan XE can be used. This instrument is used with EasyMatch QC software to allow for perfected standard data to be used and all samples of that type compared to the standard.

The above instrument excels at reflectance measurements but if analysing the dyes used in production is a requirement, then an instrument that can handle transmission measurements is a must. The state of the dye, (opaque, transparent or translucent) dictates which type of colour measurement is to be taken, reflectance or transmission. The versatile UltraScan VIS can accommodate both measurements meaning that it can take measurements at all the stages listed above; very handy for manufacturers and dyers.

Both instruments above are used in conjunction with EasyMatch QC software that can hold an unlimited number of standards and samples; this makes it adaptable to any factory’s processes and able to keep up with a change of products produced. This software also allows for comparisons from one product made to another if any changes in production processes have taken place. Pass or fail notifications can also be set to allow for operators to tell at a glance if the fabric being produced is of sufficient quality or if changes need to be made without having to analyse the data themselves.

Through the use of software, both instruments can gain the spectral data needed to be able to calculate it into the necessary colour scales and indices. The useful colour scales to use are CIE L*a*b* and its corresponding difference values (dL*, da*, db* and dE*). Delta E CMC (dE CMC) is also a good index to use; this is an elliptical tolerance that can help match different shades by providing a clear numerical value for comparison.

Depending on the purpose of the testing, brightness indices could also be used to determine the effect that cleaning products (washing powders etc.) has on the fabric itself. Z% brightness or similar may be used in conjunction with a UV filter to monitor the effect of any treatment to the finished fabric.

The simplicity of colour measurements within the textile industry is dependent on how thorough operatives need to be but it needn’t be a hard task. With all the instrumentation listed above, appearance analysis of fabrics produced can be a beneficial, simple task that can dramatically improve the quality of the finished products and allow for improvements and changes with any processes to be monitored.

Recommended Product
How to measure the colour of Fabrics

HunterLab UltraScan VIS Spectrophotometer

A host of measurement features and specialized sample-handling devices make UltraScan VIS a highly versatile colour measurement spectrophotometer. Because of its exceptional inter-instrument agreement and long-term stability, you can be confident that differences between measurements are due to product color changes, not instrument variability. Materials on the borderline of accepted tolerances will not be unnecessarily rejected.

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