Most diamonds have minute inclusions which make every diamond unique. Flawless diamonds, which are extremely rare, would be the most expensive.
The grading scale begins at "FLAWLESS" which would describe a diamond completely free of any inclusions and surface blemishes. As the inclusions become more noticeable in the diamond the stone moves down the grading scale. Gemological Services sells diamonds primarily in the VVS to SI range.
Free of inclusions or surface blemishes under 10-power magnification
VVS-1 and VVS-2
Very, very slight impurities extremely difficult to see under 10-power magnification
VS-1 and VS-2
Very slight inclusions visible only under 10-power magnification
SI-1 and SI-2
Slight inclusions easily visible under 10-power magnification
Small imperfections visible to the unaided eye (may affect durability)
Noticeable imperfections visible to the unaided eye (may affect durability)
Heavy imperfections visible to the unaided eye (may affect durability)
Many diamonds on the market in recent years have been treated to enhance the appearance of clarity by methods such as laser drilling and fracture filling. Because some of these methods of treatment are not stable, it is very important that the consumer be aware as to the presence or absence of treatment in any diamond that is being considered for purchase. The best way for the consumer to protect himself against unknowingly buying a treated diamond is to be certain that the diamond has been certified by a respected gemological laboratory such as the Gem Trade Laboratory of the Gemological Institute of America (GIA). Under the comments section of the GIA certificate any treatment the diamond has received will be noted.