COLOUR MEASUREMENTS
CIE L*a*b* colour values and reflectance (R) of samples were measured using a reflectance spectrophotometer Spectra flash 600 PLUS-CT (Data colour).From the CIE L*a*b* colour values, colour differences were calculated according to equation 1:
Where ∆L* is the lightness difference, ∆a* is the red/ green difference and Δb* is the yellow/blue difference between standard and batch. From the reflectance measurements, K/S values were calculated according to equation 2:
Where R is the reflectance, K is absorbance and S is the scattering.