The term "polish" refers to the overall condition of the surfaces of a finished diamond. A rating is assigned based on the amount of polishing lines that are visible. These polishing lines are caused by very small diamond crystals which are embedded in the polishing wheels used by diamond cutters to polish the surface of the diamond after cutting. Diamond polish is important because it can affect the degree to which light is able to pass through a diamond, rendering it more or less brilliant. Diamonds that are laboratory certified with a good, very good, or excellent polish rating are the most desirable. Diamonds that have poor polish will be less brilliant and not as desirable or valuable. Reputable jewellers diamonds are graded after examining the diamond facet by facet. They are then assigned one of these five polish ratings:
|Very Good||Not visible to the unaided eye|
|Good||May be visible to the unaided eye|
|Fair||Visible to the unaided eye|
|Poor||Visible to the unaided eye|
GIA has established a diamond polish scale. The grades are based on the visibility of polish lines or other blemishes on the skin or surfaces of the diamond. The diamond is examined by gemologists at 10x magnification when determining the polish grade:
There are not visibility of polish lines or other blemishes at 10x magnification. Light is able to perfectly enter and exit the diamond, without affecting diamond sparkle or brilliance.
There are minor polish details visible at 10x magnification. These polish lines or blemishes may have little or no impact on the diamond's sparkle. The diamond can still earn an Excellent cut grade.
There are some visible polish lines or blemishes, most likely only at 10x magnification. The diamond's sparkle may be affected because light is not perfectly able to penetrate the diamond. The diamond can earn at most a Very Good cut grade.
There are noticeable finishing errors in the form of polish lines or blemishes. These blemishes have an impact on light performance and reduce the diamond's ability to sparkle. The diamond can earn, at most, a Good cut grade.
To the unaided eye, 'excellent' and 'very good' ratings are hard to decipher. The differences become visible only when a stone is magnified. A rating of 'fair' or 'poor' means that the flaws in the polish are noticeable to the unaided eye and will have some effect on the overall beauty of the diamond.
Poorly polished facets may reduce the intensity of a diamond's reflected light or light which is refracted into and out of a diamond. This can affect the brilliance and visual performance of diamond. When a diamond has a 'good' or lower polish grading, the stone may appear as if it needs to be cleaned.
For diamonds with a polish grade of Excellent to Good, any polishing defects are not visible to the naked eye, and should have no impact on the diamond's overall appearance.
For diamonds with clarity grades of I1 or lower, even a polish grade of Fair is acceptable, since these diamonds already possess internal inclusions that are visible to the naked eye, making any polish markings less relevant. An inclusion is an internal flaw in the diamond. The position, size, number, color, and reflectivity of a diamond's inclusions has a significant impact on its appearance and value. Clarity refers to the degree to which these natural flaws are present. Diamonds graded by the GIA and other labs have their clarity rated on a scale of F (flawless) to I3 (significant inclusions).
For diamonds less than 0.75 carats, any polish grade of Fair or better will not affect the appearance of the diamond to an untrained observer.
Poor is the only polish grade that should be avoided regardless of the size or clarity of the diamond.
Feature 1 - Polish Lines: Small grooves located on facets resulting from diamond polishing. You can tell they are difference from surface graining because they do not cross facet junctions. Only when extreme, they can affect a diamond's sparkle.
Feature 2 - Abrasion: Small nicks and cuts along the junctions where facets meet. Typically a result of wear and tear.
Feature 3 - Extra Facet: During manufacturing, an extra facet is manufactured on a diamond, typically in order to remove an inclusion.
Feature 4 - Lizard Skin: A bumpy looking surface on the facet that almost looks like natural rough diamond skin.
Feature 5 - Nick: A small notch on a diamond's surface that doesn't appear to have depth. It can be like a very minute chip.
Feature 6 - Pit: A tiny white dot on the surface of skin that resembles a pinpoint.
Feature 7 - Natural: A portion of rough diamond skin that remains on a surface during the manufacturing process. Typically, it occurs near the diamond's girdle.
Feature 8 - Burn Mark: A whitening of the diamond surface resulting from excess heat applied during the polishing process. It is very difficult to reverse a burn mark on a diamond.
Feature 9 - Rough Girdle: Rough skin patches on the girdle that cannot be polished away easily.
Feature 10 - Scratch: A small line on the surface of the diamond that doesn't appear to have depth. It is very difficult to scratch a diamond. A scratch can be repolished away.
Ranges from no polish features to a few minute features that can be viewed with difficulty face-up at 10X magnification.
Some typical features that would establish an excellent category include a few pits or nicks, a small area with faint transparent polish lines or negligible scratches or abrasion.
Minor polish features are seen face-up at 10X magnification.
Some typical features that would establish a very good category include several pits or nicks, a few small areas of abrasion, a limited extent of moderate transparent polish lines, a small area with faint white polish lines, several faint scratches or a few heavier white scratches, a faint lizard skin or a small area of very faint burn.
Noticeable polish features are seen face-up at 10X magnification. The luster of the diamond may be affected when viewed with the unaided eye.
Some typical features that would establish a good category include moderate to heavy transparent polish lines, white polish lines, many heavy scratches, lizard skin or burn.
Obvious heavy polish features are seen face-up at 10X magnification. The luster of the diamond is affected when viewed with the unaided eye.
Some typical features that would establish a fair category include heavy white polish lines or burnt facets over most of the crown or pavilion.
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.
Some typical features that would establish a poor category include heavy white polish lines or burnt facets over most of the crown and pavilion.
Note - Some features were enlarged for the purpose of illustration; it is the appearance at 10X magnification that is considered during evaluation. Note, too, that each finish category encompasses a range of appearances and the selected examples do not represent the highest or lowest point of that category.
Of the recorded attributes on the GIA report, the polish grade has the least impact on the diamond's price and value. With updates in technology, a larger percentage of diamonds earn a Very Good or Excellent polish grade, especially in round cut diamonds. Therefore, if you find a diamond with a Very Good cut grade and that is part of the reason for a good value, it may be well worth your while.