Color analysis
A Labscan XE colorimeter (HunterLab, Inc., Reston, VA.) with the UV
filter at nominal position, calibrated with standard white and black
plates was used to analyze the color of oil samples. Oil was resented in
a sample cup with a black ring and a white disk covered with a black
sample cover. Three readings of each sample were recorded. The mean
values of the color coordinates L* (lightness - darkness), a* (redness -
greenness), and b* (yellowness -blueness) are reported.