Purity, also called clarity of diamond, is with its color a criterion difficult to appreciate for non gemologists.

This is a comparative classification criterion for diamonds based on the number and size of inclusions (various impurities) present at the heart of the crystal and surface defects of the gemstone. This is one of the 4 criteria for assessing white diamonds quality.

The purity index is evaluated by a gemologist with a magnifying glass x10, analyzing diamond under a cold light (typically LED) held by tweezers on a white background.

Putity classification diamond

A magnifying glass x10, tweezers, a white background and a cold light are essential to appreciate diamond purity.

 

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Classification scale of diamonds purity

The following table shows you how diamonds are classified according to the number and size of impurities they present. To summarize this table, the more the impurities will be visible, the more diamond purity will be discounted.

diamond clarity scale

Different types of diamond imperfections

There are many types of inclusions and surface imperfections that can present a diamond, here they are presented as you will find on your report of diamond quality or certificate developed by a gemological laboratory :

  • Crystal : presence of a mineral deposit in the heart of diamond generally seen dark or black
  • Pinpoint : presence of a very small crystal often perceived whitish color
  • Cloud : presence of a tight group of small crystals not visible individually
  • Cavity : presence of a depression on the diamond surface
  • Chip : presence of a chipping on the diamond surface, most often caused during cutting
  • Bruise : presence of a chipping on the diamond surface most often involving a fracture in the crystal for origin
  • Feather : the presence of a fracture with fine lines emanating from it, recalling the motif of a feather
  • Needle : presence of a fracture in the shape of a line (like a needle)
  • Twinning wisp : presence of a flat ribbon of small crystals caused by a natural crystal distortion
  • Natural : presence on the surface of a small portion of unpolished rough diamond, generally present at the level of the girdle
  • Indented Natural : presence of a Natural defect causing a small cavity on the surface
  • Extra Facet : presence of an additional facet not part of the diamond cut standard considered

To visualize these faults in a concrete way, consult the interactive diagram on this page.

Treatments to improve diamonds purity

Because diamond price depends heavily on its degree of purity and since almost all diamonds have surface imperfections or inclusions, different techniques have been developed to either eliminate these defects or make them less visible.

Treatment improving purity

Photo showing a diamond with inclusions before laser treatment and after treatment (source photo)

  • Acid treatment : diamonds are soaked in an acid bath that doesn't attack the crystal lattice of carbon but dissolves all the impurities and crystals present on its surface. This operation is very common and economical.
  • Laser perforation : this technique is used when diamond imperfections are within the crystal lattice and inaccessible from the outside. A laser is used to punch the diamond, creating a channel from the surface to the imperfection. If the imperfection was a crystal, it can now be treated with acid to make it disappear. The hollow cavity is then much less visible than the dark crystal present before.
  • Fracture Filling : this technique is used after laser perforation, when the acid-treated crystal has disappeared and left a cavity within the diamond. A special compound is then injected into the cavity which will prevent the light from being reflected on the walls of this cavity. The cavity is then always present, but made almost invisible. This technique was developed by Yehuda of Yehuda Diamonds.

    Perforation laser treatment

    Photo showing the result of a laser perforation used to remove a foreign crystal inside the diamond (photo source).

    If the first two techniques for improving diamonds purity are tolerated by the GIA, it's different for fractures filling. This institute refuses to certify such diamonds. It should be noted that other laboratories do this, specifying that diamond purity has been improved in the certificate comments.

    Be careful, don't think that such treated diamonds are of poor quality, on the contrary, they're natural diamonds offering a beautiful rendering at a lower price, so it can be a good option if you're looking for a diamond big enough for an affordable price because they're cheaper than diamonds of purity equivalent naturally.

    Anyway, you'll have to turn to a gemologist or choose a certified diamond to find out what it is.

     

    Free Bonus : Download our complete guide on Diamond (fr).

    You'll discover all you need to know to buy diamonds jewelry online or in store.

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    August 08, 2019 — Hugo Maherault

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