When looking to purchase a Diamond, there are a few more factors to consider than just the 4 C's, (Cut, Color, Clarity & Carat Weight).  You will want to look at Cost, and one of the most overlooked criteria, but one of the most important; Certification.  A Certification is different than an appraisal.  An Appraisal puts a value on the item you have purchased, and is often used for retail replacement.  A Certificate is done by an independent laboratory, and certifies the quality of your stone, but does not place a monetary value on it. There are many labs that issue certifications, but they do not all grade at equal standard levels. The Gemological Institute of America (GIA) and the American Gem Society (AGS), are the two most recognized and respected laboratory in the world.  They set the standard for the entire diamond industry.  If you choose to buy a non GIA or AGS certified diamond, understand that what they say you are getting and what you are actually getting, could be quite different.

Certifications for colored stones are not as common. It is hard to standardize the colored stone industry.  If you are going to get a certified colored stone, GIA and AGS, are the most trusted and recognized.