What is the difference between a "certified diamond" and a "non-certified diamond"?
There is no physical difference between a diamond that is certified and one that is not. A certificate does not change the nature of a diamond in any way. The difference between a certified and an uncertified diamond is that, with the certified diamond, you have tangible, legal assurances as to the particular nature and quality of the diamond you are purchasing.
A certified diamond comes with a diamond grading report guaranteed by an accredited gem lab. This report assures that the diamond is independently recognized as possessing all the qualities specified by that report. When you buy a certified diamond, you are getting a diamond with beauty and pedigree.
An uncertified diamond is not necessarily a bad diamond; certainly, it can be as beautiful as its certified counterpart. Below are some reasons why you would want to buy a certified diamond.
A diamond grading report adds value to a diamond. The quality assessments made by independent labs, such as GIA or AGS, are recognized worldwide. These quality assessments are used by appraisers to determine the insurance or replacement value of your diamond. If you purchase an uncertified diamond, there is no guarantee that the appraiser will appraise your diamond at the same level at which the jeweler who sold it to you did.
A quick note on how reports from various independent labs compare with one another: GIA and AGS are considered the industry leaders, and the final word on gem quality, among diamond dealers worldwide. While plenty of other independent labs exist, some are a bit lax in their assessments of diamond quality and do not command the same respect for consistency and quality of grading that GIA and AGS do. For this reason, if you are in the market for a diamond, make an effort to buy only GIA- or AGS-graded diamonds.
A diamond grading report adds an increased comfort-level to your purchase. Because the quality of your purchase has been independently verified, you can feel assured that you have made a wise purchase and that you have received exactly what you have paid for.