**3.4 Effect of variability in measurement of colour value of textiles**

Colour Matching of textiles is very much dependant on the Pigment /dye Database created –dye class based and type of fibre/fabric based and dye company based to be pre-up-loaded in spectro. To match full strength of colour, Light and dark i.e. white and black reduction are very important.

Pigments /dyes should be thoroughly dispersed and uniformly dyed, which is Very difficult with powder pigments, but much easier with Master batch mass pigmentation to produce coloured textiles.

There are so many variations in measuring surface colour of textiles. A measurement is never perfect. The effect of variability of colour measurement is reduced by using multiple measurements and taking avrages at 10 points atlesat. How many measurements should I make for averaging is a good question and Rule of thumb is 10 times atleast for each variability parameter of dyeing for standardising dyeing process variables. For any variable instrumental factors also, measure each spot of colour value for 10 times to take average of it. But for sample uniformity for data base storing data, one should repeat colour measurements at several locations — more than 10 to 100, depending CV % of K/S values or reflectance values of coloured textile surface. One can follow ASTM standard E 1345- 90 to determine how many measurements are necessary in each case.

Some more Practical Aspects of variability in colour mesurement of textile surface [9] are:


The reasons of variation of colours produced in textiles during data base preparations - are


Moreover, different other cares are necessary, without which in-accurate measurement occur for measuring of colour values of textiles –e. g.


Use of Pigment colouring for small quantities where Master-batch development is easier.

#### **3.5 Areas of application of computer colour measuring and matching system**

1.Measurement of tristimulus values, reflectant at maximum absorbance wave length or K/S measurement of transmitants.

#### *Basic Principles of Colour Measurement and Colour Matching of Textiles and Apparels DOI: http://dx.doi.org/10.5772/intechopen.101442*


## **4. Surface appearence measurement in terms of whiteness, yellowness and brightness indices**

Whiteness is assesment of freedom from any colour and contamination/stain / soil and as such it is taken as an indicator of quality for a bleached textile fabric prepared for dyeing. Objective measurement and meaningful numerical expression whiteness index as per CIE and Hunter lab scale are widely used. It represents whiteness index (WI) in terms of colorimetric values for the specimen and the chromaticity coordinates of the illuminant:

$$\text{WI}(\text{CIE scale}) = \text{Y} + 800(\mathbf{x}\_{\text{n}} - \mathbf{x}) = \text{1700}(\mathbf{y}\_{\text{n}} - \mathbf{y}) \tag{23}$$

$$\text{WI(Hunter Labor-Scale)} = \text{L}^\* - \text{3b}^\* = \text{10} \sqrt{\text{Y}} - [\text{21(Y} - \text{Z96})] / \sqrt{\text{Y}} \tag{24}$$

where x, y and Y are the colorimetric values for the sample under illuminant D65, and xn and yn are the chromaticity coordinates of the light source/illuminant used. A value for WI of 100 represents a perfect reflecting white diffuser, equivalent to surface of saturated paste of Magnesium sulphate.

X, Y and Z are the CIE tri-stimulus values of the sample and *L*\* is the lightness/ darkness indicator, *b\** is the blueness/yellowness indicator.

Similrly, yellowness indices [12] as per ASTM-E313/1973 can be expressed as follows:

$$\text{Yellowness Index (YI)} (\text{ASTM-E313/1973}) = 100 \ \left[1 - (\text{B/G})\right] = 100 \left[1 - \frac{0.8477}{\text{Y}}\right] \tag{25}$$

Where, X, Y and Z are the CIE tri-stimulus values of the sample, *L*\* is the lightness/darkness indicator, *b\** is the blueness/yellowness indicator and B = Z/1.181 = 0.847 Z, G = Y = L2/100.

Brightness Index (BI) as per ISO-2469/2470-1977method [13] can be calculated by following formula:

Brightness index ¼

$$\frac{\text{Reflectance Value of the Sample at 457 nm}}{\text{Reflectance value of Standard white diffusivity (white tiles) at 457 nm}} \times 100\tag{26}$$

Treatment with fluorescent brightening agents can lead to reflectance values of up to 150. Although the pattern appears to become whiter, the change in appearance is due to a change in chroma towards blue, and this fact is expressed in quantitative form as the 'tint factor'. Allied to the appearance of the uncoloured fabric is the yellowness, which suggests yellowing by chemical treatment or by heat scorching or degradation by light or by gases. Thus along with colour parameter the said other surface appearance properties are also very very important too in defining the quality of the surface appearance of any textiles.

### **5. Importance of colour measurements and matching in garment industry**

Colour is one of the important element of a design. Colour with aesthetics / texture of anty textile fabrics / garments are as important as its physical and functional property criteria. Matching of colours, especially in specific textiles made from specific or different fibres and their blends is very very crucial in many applications. The task of communicating and measuring and matching of colour becomes more difficult when colours need to be exactly matched with a given standard supplied for different textiles. More and more precision colour matching is required in specialised textile products like defence dress materials, school uniform etc. and also for matching suits for consumer textiles and livestyle products for matched furnishings, bed linen and auto Interiors etc.

This Computer aided reflactance spectrophotometer is an impoartant tools/ intrument for quality up grdation of textiles and garments by maesuring surface colour strength and colour dierences values as per CIE equations/ formulae. Some Other Application of computer aided colour measuring cum matching System used in textiles or apparel industry's Dye House:


*Basic Principles of Colour Measurement and Colour Matching of Textiles and Apparels DOI: http://dx.doi.org/10.5772/intechopen.101442*

