The proportions and finish of a polished diamond determine its final face-up beauty. A well proportioned diamond will return most of the light back to the eye for maximum brilliance and dispersion.
Sparkle is created by the facet placement and the surface polish.
How a diamond handles light:
- When a diamond is cut to good proportions, light is reflected from one facet to another and then dispersed through the top of the stone.
- If the cut of the diamond is too deep, some light escapes through the opposite side of the pavilion.
- If the cut is too shallow, light escapes through the pavilion before it can be reflected, thus reducing brilliancy.
Brilliance: is the total light reflected to the eye from both surface and internal reflections.
Dispersion: is the separation of white light into its spectral (rainbow) colors and is caused by its refraction, which bends each wavelength of light a little differently to cause separation into individual colors.
Scintillation: is the flashing or sparkling of light which occurs when either the diamond or light source are moved.
Finish: which includes polish and symmetry, is also an important contributor to a diamond's beauty.
Polish: features largely describe the condition of the surface of the stone, and include abrasions of the facet junctions and the culet, rough and bearded girdles, nicks and pits, and scratches and polishing marks if they do not affect the clarity grade. You will remember some these elements were also listed as blemishes in the clarity-grading scheme.
