Diamond blemishes are all the fun stuff on the outside of a diamond…
Pit – A tiny opening that doesn’t extend into the diamond. It might have been an inclusion that was present in the diamond rough but didn’t get completely polished away during the cutting process.
Nick – A small chip on the girdle or a facet edge that doesn’t extend into the diamond. Most likely a sign of some wear and tear as the stone has been worn.
Abrasion – Tiny nicks along the facet junctions producing white fuzzy lines instead of sharp facet edges. Again a wear and tear issue. Can also be seen when many diamonds are kept together in a jewelry box or travel pouch, “paper worn” as it’s called in the trade…. this is when gemstones are kept in a paper parcel or plastic bag, they end up rubbing together during normal handling.
Scratch – A fine white line, curved or straight. Remember only one thing can scratch a diamond!
Natural – Part of the original rough diamond’s “skin” that hasn’t been completely polished away. Normally seen around the girdle area.
Polish Lines – Fine parallel grooves and small ridges left on a diamond’s surface during the polishing process. This occurs when the diamond cutter’s polishing wheel is in need of resurfacing.
Polish Mark – A whitish cloudy film on the surface of a facet from excessive heat during the polishing process. Diamonds can get red hot while being polished and the surface can actually start to burn.
External Surface Graining – This occurs when the diamond is being formed…. the growth orientation changes direction and so when it is being polished it is difficult to get a perfectly smooth surface. This is just like the grain you can see and feel in a piece of wood.
Extra Facet – This is done when there is some something on or near the surface that would the Clarity grade if it was left untouched. The diamond cutter will polish away the imperfection and so it leaves a facet that is not part of the symmetrical layout of the facets. Many times this can be seen on or near the girdle area.
– Important Take Away Points –
Diamond blemishes are usually only a very minor component of determining the diamond’s clarity, however… as a diamond is worn it might start to accumulate a lot of chips and nicks, especially around the outer edge (the girdle) of the diamond.
The girdle should be just thick enough to protect the stone but no thicker because a thicker girdle only starts to add additional weight to the diamond without any greater beauty. The crown angle also should be set to a proper amount (34.5°) and not to a shallow angle, this makes for a thin crown portion of a diamond. Usually a medium girdle along with a proper crown angle, will provide for a stronger diamond.
Most diamond blemishes can be polished away if they become too numerous and it would warrant the time, trouble, and expense of having the diamond recut.