Why does a diamond sparkle the way it does?

A diamond's sparkle is the direct result of how its facets redirect light, and that behavior is identical in lab-grown and mined stones because both share the same crystal structure and refractive index of 2.42. The visible effect breaks into three components: brilliance, which is white light reflected back through the table; fire, which is the dispersion of light into spectral color; and scintillation, the contrast pattern of bright and dark areas as the stone moves. Cut quality controls all three. An IGI cut grade of Excellent or Very Good indicates the proportions and angles needed to maximize each component. A poorly cut stone, regardless of color or clarity grade, will appear flat. When comparing lab-grown diamonds, prioritize cut grade above other variables. A well-cut 1.00 ct lab-grown diamond will consistently outperform a poorly cut stone of larger carat weight.