Color measurement of the powder samples was carried out using a
HunterLab Color spectrophotometer (I-5 Model, GretagMacbeth). The
results were expressed in terms of L, a and b values, where ‘L’ was
used to denote lightness, ‘a’ to redness and greenness and ‘b’ to
yellowness and blueness. Chroma, indicating color intensity, was
calculated by the formula (a2 + b2
)
1/2. The hue angle (H°) was calculated
by the formula H° = tan−1 (b / a).