Understanding Diamond Polish Grade

In the GIA Diamond Grading System, “Polish” refers to the quality of a diamond’s surface condition as a result of the polishing process or the blemishes created after the cutting process, often referred to as “wear and tear” during the cutting process. Polish features are located on the surface and do not visibly penetrate into the diamond at 10X magnification. Polish is assessed on a scale consisting of Excellent, Very Good, Good, Fair and Poor.

Polish Imperfections

Below a number of features are considered in the evaluation of Polish.

  • Pit: tiny opening appearing as a white dot.
  • Nick: small notch on a facet junction, usually along the girdle or culet; minute chip with no visible depth at 10X magnification.
  • Scratch: surface mark is normally seen as a fine white line, curved or straight.
  • Abrasion: area of minute scratches or pits along a facet edge producing a fuzzy white line instead of a sharp facet junction.
  • Polish lines: parallel lines left by the polishing process; may appear white or transparent.
  • Lizard skin: transparent uneven texture confined to one facet; caused by polishing a facet off-grain, at the hardest direction near a cleavage plane.
  • Burn mark or burned facet: whitish haze across a facet or on a concentrated area caused by excessive heat during polishing or occasionally by a jeweler’s torch.
  • Rough girdle: irregular pitted or granular surface of a bruted girdle due to pits and nicks.

Polish Grading Categories

Diamond graders consider the amount and visibility of the polish features present. The general appearances of GIA’s five Polish Categories are:

Excellent: ranges from no polish features to a few minute polish features that can be viewed with difficulty face-up at 10X magnification.

Very Good: minor polish features are seen face-up at 10X magnification.

Good: Noticeable polish features are seen face-up at 10X magnification. The luster of the diamond may be affected when viewed with the unaided eye.

Fair: Obvious heavy polish features are seen face-up at 10X magnification. The luster of the diamond is affected when viewed with the unaided eye.

Poor: Prominent heavy polish features are seen face-up at 10X magnification. The luster of the diamond is significantly affected when viewed with the unaided eye.

What is the Polishing Process?

Both cutting the facets of the diamond and the final polishing are included in the polishing process. For the faceting process, a diamond cutter creates each facet using a dop to hold the diamond at the correct angle, grinding the diamond against a blade while spinning it with diamond powder and lubrication like oil or lanolin. This process is repeated for each facet of the diamond. A polishing wheel and polishing pads are used to polish faceted diamonds and are a time-consuming process. This stage is for removing any coarse marks left from faceting the diamond and for ultra-fine polishing to bring out all the light-reflecting properties of the diamond.

Diamonds are unlike any other material on earth. Most gemstones can be polished with substances that are harder than themselves, however, there is nothing harder than a diamond; hence diamonds must be polished with diamond dust. Diamond carbon atoms are tightly packed in a lattice-like an arrangement which means careful attention must be paid to determining the graining direction of the diamond, if a diamond is polished in the wrong direction, damage to the diamond will result.

Is it Necessary to Spend More for an Excellent Polish Grade?

The feature that most commonly affects the perfection of the diamond’s surface is microscopic polish lines, this blur the diamond’s surface. These surface grain lines occur because of variations in hardness or grain of the facets. If these lines are very pronounced they will be able to be seen with the naked eye. Most often you will need a jeweler’s loupe to be able to view these lines. If your diamond has anything upwards of a “Good Polish” grade you will not see any of these marks with the naked eye, however lower polish grades lower the luster of the diamond.

Final Tips:

  • Avoid Fair and Poor Polish Grades
  • Excellent and Very Good Polish Grades are most desirable
  • Excellent Polish Grades can be found at reasonable prices relative to all other grades
  • Diamonds having superior cutting grades should take precedence over Excellent Polish Grades.
  • Always pay particular attention to entries under Keys To Symbols

This article was contributed by Frank Fisher.

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learn everything you need to know before you buy a diamond in this detailed book!

learn everything you need to know before you buy a diamond in this detailed book!