Cut

Diamond has total internal refraction so to maximise it’s brilliance the cut is extremely important. If the cut is done well the stone has a wonderful lustre. If done badly, even the best diamond will look flat, dull or even “fish eye”. A term used when the cut is too shallow.

GIA Classification of cuts read as follows:

Excellent
Very Good
Good
Fair
Poor

For more detailed information please go to the official GIA website.