After grading the color the gemologist checks for fluorescence. When exposed to ultraviolet light about 50% of diamonds will fluoresce or emit light. They usually fluoresce a blue color under long wave ultraviolet light, but yellow, pink, or green fluorescence is also possible.

The fluorescence of diamonds is judged under a long wave ultraviolet light.

On the grading report the strength of fluorescence is noted as “None,” “Faint,” “Medium,” “Strong,” and “Very Strong.” If the fluorescence is greater than faint, we also note the color, i.e. – “Strong blue.”