Evaluating color (whiteness) in person

[bar01]

I found many questions and answers about light sources and visual evalaution of fire and brilliance.

But light can affect perceived color too - right? It reflects what it exposed to. If the light sources are slightly blue, yellow, or white then the color would reflect this too?

What is the best way for a normal person to visually evaluate the acceptable level of "whiteness" of a loose diamond? Under diffuse natural sunlight? Halogen lighting sources, or others? Against my skin (between my fingers)? On a white piece of paper?

If this was discussed in another post - sorry.

 

[denverappraiser]

Difused natural light on a white sheet of paper.

This is tough because you are, presumably, wishing to compare several stones that aren't going to all be in the same place at the same time. This means you have differences because of the time of day, the actual color of the paper, and quite a few other things. The paper sellers have lots of products that they call 'white'. It's the reason that the pros always have a known comparison stone and do it with a standardized light source and background that they can repeat for every stone. If you aren't able to repeat these things every time, it's almost impossible to have an accuracy to within a grade or two and even that takes practice. Even with this there is a fair amount of disagreements that come up about color.

Neil Beaty, GG ISA
Independent Appraisals in Denver