Poor or Inferior Cut diamonds are diamonds that do not reflect a good amount of light and seem dull. Deep Cut diamonds are diamonds that have extra weight on the bottom that results in a dark appearance in the center of the stone. Too Shallow Cut diamonds will look glassy and have reduced brilliance. Instead, our results suggest that there are many combinations of proportions that would yield equally 'bright' round brilliant diamonds. Dispersion is the amount of rainbow colors returned to the eye from within the diamond.
White light separates into spectral colors, each of which vibrates at different frequency.
As light passes through an optically dense material, such as a diamond, different wavelengths are refracted to different degrees and have slightly different refractive indices. Dispersion is usually expressed as the difference between the RI's of the red and violet rays. Diamond's dispersion is 0.044. Doublet is an assembled stone made up of a crown and pavilion cemented or fused together. Doublets designed to imitate diamond may be composed of colorless synthetic or natural sapphire, synthetic or natural spinel, quarts, or glass.