Legolas, one of the diamond grading traditions is that the best time to color grade diamonds is in the morning, and that a color grader should grade continuously for no more than one and a half hours.
Another tradition is that a window positioned to receive northern daylight is considered the best location for color grading.
Both of these traditions are valid, although not usually followed rigorously in today's hustle-bustle diamond world. The reason for the morning grading (for no longer than 1.5 hrs) is that your eyes start out fresh, and then you knock off before they get fatigued.
The reason for northern daylight is because of the diffused lighting received from that direction. It's the easiest to color grade with. Southern lighting is more difficult, in that it can throw "color" into the grading scenario.
Today's diamond graders out of necessity and workload usually skirt around these traditions by using full spectrum fluorescent lighting and copious amounts of coffee...
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Sarasota Gemological Laboratory
