The details of a diamond’s cut are referred to as its finish. Finish is made up of two categories; Polish and Symmetry. Polish is the overall condition of the diamond’s facet surfaces and symmetry is the exactness of the shape and placement of its facets.
Diamonds that are well polished will look brighter and will produce sharper light reflection than those that receive a lower polish grade. Poorly polished diamonds may reduce the light reflected to, into, and out of the diamond even if it has the best proportions possible.
Because of their hardness, diamonds can take a better polish than any other gemstone. Polish characteristics can be a result of the finishing process or be affected by blemishes created after cutting. Polishing characteristics are caused by the minute diamond crystals embedded in the polishing wheel used by a diamond cutter to polish the surface of the diamond. When gem laboratories evaluate polish, the diamond is examined under 10x magnification and the Gemologist will examine the diamond facet by facet. They look for blemishes that don’t affect the clarity grade.
A diamond’s polish grade and the abbreviation of the polish characteristic are listed on all diamond grading reports.
The GIA polish grades are: Excellent (E), Very Good (VG), Good (G), Fair (F), and Poor (P)
The AGS polish grades are: Ideal (AGS 0), Excellent (AGS 1), Very Good (AGS 2), Good (AGS 3 and 4), Fair (AGS 5, 6, 7), Poor (AGS 8, 9, 10)
Common polish characteristics
Abrasions (ABR) – minute nicks along the facet junction that look white and fuzzy
Burn mark (Brn) – whitish haze across a facet caused by excessive heat
Lizard skin (LS) – wavy or bumpy area with a transparent pitted texture
Nick (Nk) – small notch on a facet junction with no depth when viewed under 10x magnification
Pit (Pit) – very tiny opening that looks like white dot
Polish lines (PL) – fine groves and ridges left by the polishing process
Rough girdle (RG) – an irregular girdle surface
Scratches (S) – thin tiny white lines across the surface of the diamond that have no depth
Surface grain lines – transparent line that is part of the grain of the diamond
When budget allows, Since 1910 recommends purchasing a diamond for an engagement ring with a polish grade of Good or higher.