Fabric lustre and colourfastness
- The light reflectance of fabric is referred to as the colourfastness and lustre properties.
- Colour is one of the most important factors in consumer acceptance of fabric materials and in terms of their applications at end usage.
- The colour appearance of an object depends on the source of illumination, the object’s interaction with light, and the response of sensors in the observer’s eye to the light reflected from the object.
- Current technology offers the possibility of measuring colour very precisely. Two theories the tristimulus theory and the opponent theory are used as the basis of instrumental colour measurement.
- The CIELAB colour system is widely used in the colour measurement of textiles. The CIELAB values L, A, and B are mathematically derived from the tristimulus colour values X, Y, and Z-axis.
- CIELAB provides a method for quantifying colour differences into a single term. The overall colour difference between two specimens can be designated by the term ΔE.
Measurement of the colour of the fabric
Fabric colour measurements can be classified according to their sophistication and precision in colour measurement.
The measurements of colour include the components of colour, the specimen viewing geometry, and instrument portability.
In this type of instrument, a light source, a port or opening onto which the specimen is placed, and a detector are provided.
The number of colour sensors that sensed the specimen colour affects its accuracy in colour measurement.
To measure the colour of any specimen, some instructions need to be followed.
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| Spectrocolorimeter |
To measure the colour of the specimen first proper Instrument setup is required. The measuring instrument has to be set up in the proper mode before colour measurement, according to the instrument manufacturer’s recommendations.
I.e. - in the case of a sphere-type reflectance spectrophotometer, the possible list of parameters to be set up includes the spectral range, the polychromatic/monochromatic mode, the specular component in/out, the sample port size, and the selection of filters. With the instrument set up, it must calibrate properly. (To clarify this first arrange a mock test of the instrument for known coloured objects.)
The performance of the instrument in terms of precision and accuracy can be checked by the measurement of colour standards with calibrated spectral data.
For testing, A standard-sized Sample is prepared. It is then placed into a condition in a room or chamber with controlled humidity and temperature for a suitable period before colour measurement.
The sample usually is folded to complete opacity to avoid background influence during colour measurement.
All samples to be inter-compared are folded into the same number of layers. Colour measuring instruments are generally designed for the measurement of flat samples to be placed at the sample port therefore extra hairiness is removed from the sample.
(If the sample extends inside the port or is displaced away from the port, different measured readings may result. If the textile sample flatness is difficult to achieve, due to surface texture, measurement behind the glass will help. However, the measurement results must be corrected for effects of the cover glass, such as the Fresnel reflection.)
There are three types of instruments: colourimeters, spectre-colourimeters, and spectrophotometers.
The principles of colourimeters and spectrophotometers are the same.
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| Fabric colour identification test |
Colourimeters determine the reflected colour of a specimen using three sensors that respond to red, green, and blue. However, colourimeters don't have a wide range of the colour spectrum.
While in the case of spectra-colourimeters, it is more accurate and has more colour sensors that sense particular intervals of the spectrum.
The accuracy of colour depends on the number of sensors, which can be between three and 16.
Spectra-colourimeters can provide more flexibility in the choice of illuminants than is possible in colourimeters.
Spectrophotometers are the most accurate of the three levels of instruments and can safely be used to set colour standards. Spectrophotometers sense the reflected colour of a specimen at several individual wavelengths within the visible spectrum, at either 10 nm intervals or 20 nm intervals throughout the visible spectrum.
The instruments are sometimes referred to as 16-point or 31-point instruments according to the number of measurement points across the visible spectrum, 400–700 nm.
Some textiles have colourants that are sensitive to heat and light. Colour change on exposure to heat and light is called thermochromic and photochromism respectively.
Both the thermo-chromic effect and the photochromic effect can be eliminated or reduced by minimizing the time of sample exposure to the illuminating source during measurement.
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| Fabric colour identification test |
- What is fabric lustre?
- What is colourfastness?
- How colorfastness is measured?
- What is spectrocolormeter?
- How fabric color is identified?
References
Booth, J. E. :. (n.d.). Principles of textile testing an introduction to physical methods of testing textile fibres, yarns, and fabrics. London: National Trade Press Ltd,1961. from https://www.abebooks.co.uk/Principles-Textile-Testing-Introduction-Physical-Methods/19989810376/bd
Cenote, M. (2015). Google Books. In The SAGE Guide to Key Issues in Mass Media Ethics and Law (pp. 847–858). SAGE Publications, Inc.
Ferreiro López-Riobóo, J. I. (2015). Long-term (2001–2012) study of a proficiency testing scheme for textiles. Accreditation and Quality Assurance, 20(4), 239–245. https://doi.org/10.1007/s00769-015-1128-1
Burkhart, M. (n.d.). 5 colour fastness tests to prevent textile fading and staining. Intouch-quality.com. from https://www.intouch-quality.com/blog/5-color-fastness-tests-to-prevent-textile-fading-and-staining
Trivedi, Y. (2020, April 14). Colour fastness in Textile testing. Textilesphere.com. https://www.textilesphere.com/2020/04/colour-fastness-in-textile-testing.html
(N.d.). Textilelearner.net. from https://textilelearner.net/different-types-of-colour-fastness-test/
- Part-1 Fabriccolourfastnesss introduction
- Part-2 Fabric Colorfastness properties and affecting factors
- Part-3 Fabriccolourfastnesss towards various factors
- Part-4 Measurement of fabric colourfastness by sunlight, washing, and perspiration
- Part-5 Measurement of fabric Colorfastness by crocking or frosting and gas fumes
Writer - DSPAT Team
