Clarity is one of the four c's you consider when you are purchasing your diamond. It is a pretty important one too as inclusions or natural flaws can impact on how well a diamond can refract light; "sparkle".
Clarity enhanced diamonds usually started out as an I1 or I2, the lowest grades on the clarity scale. A lazer is used to clean out the inclusion, a resin; molten glass and boron solution, is then injected into the flaw. The diamond is then re-polished so you are unable to see where the enhancement has been done. The diamond then appears to be a higher clarity grade.
Although the grade may appear to be higher to the naked eye, a trained gemologist will be able to see the resin with their specific equipment. But what you can see with the naked eye, is a diamond that may now be labeled as VS2, but does not sparkle as nicely as what you would expect it to. This is because the resin, although hiding the inclusion, does not allow for any more light refraction than when the diamond was I2.
A jeweller who is selling these diamonds must disclose that the diamond is clarity enhanced and also is obliged to advise of the cons that go along aside purchasing one of these diamonds. The most common and most annoying of which is enhancement reversal.
Clarity enhancement is not permanent, even though many jewellers will claim it to be so. If a jeweller is advising you that clarity enhancement is permanent then they are purposefully misleading you.
The resin does not like strong UV rays, so sunbeds and even some bright sunlight can reverse the enhancement over time. The resin also does not like acid. You must advise your local jeweller if your diamond is enhanced because if he/she is unaware and is repairing or even cleaning your ring the enhancement can reverse! Diamonds with enhanced clarity have reversed just by being placed in a jewellers ultrasonic cleaner!
No matter how well you treat your diamond over time the resin will change to have a greyish tint giving the diamond a very unpleasant appearance.
I do not recommend anyone purchase these diamonds. Although the lower price for a larger stone might seem attractive in the first instance, this is a false economical view.
I have had very disappointed customers arrive in my store with their diamond clarity enhancement reversed wanting to know what their options are now. These clients have bought these diamonds off dodgy jewellers. They have not had the true nature of the enhanced diamonds explained to them and would never have considered buying one if they had.
The Gemological Institute of America will not issue a grading report for clarity enhanced diamonds. This to me this says it all! It is my recommendation to not buy enhanced diamonds, they just end up being a huge disappointment, especially to the person wearing the ring!