I am looking for the color grading manual. How do you describe alexandrite colors? Are there any grading specifics or rules? How should I evaluate alexandrite color change?
There are no international standards to grade the strength of color change in alexandrite and the better labs may use master stones to grade the strength of a color change. Most labs use something like strong, moderate, or weak to describe the strength of a color change. For color grading, the GIA system is the most convenient and they offer a program called something like gem Ewizard that is useful. There is some variation as a function of the monitor you are using. Although the system is not perfect, it is the best practical system to grade colored gemstones and we use it.