There are many organizations/labs that certify diamonds - a diamond certification is a document that notes a diamond has been graded by an outside source, and lets the client know specific details of the diamond they are purchasing.
A debate has broken out as weak and incorrect diamond certifications have infiltrated the market. How do you know what you’re buying if the certificate is incorrect? Working with a diamond professional will help answer questions and alleviate concerns you may have about purchasing a particular diamond - make sure to have an expert your side!
A respected, well-known lab is GIA - the Gemological Institute of America. GIA is a nonprofit institute that has been in action since 1931 - their grading has become the benchmark for certification standards. While diamond grading can be a little subjective, GIA is very consistent in their system and produce reliable certifications.
There is absolutely nothing wrong with a diamond that is not certified by GIA - it’s still a diamond! You just cannot compare it “apples to apples” with a GIA certified stone. The grading could be correct, but it could also be 4 grades off GIA standards, depending on the lab and what kind of day the particular grader was having when he or she looked at the diamond.
Some clients choose to purchase non-certified or non-GIA certified diamonds. If you are working with a trained diamond professional, often times you can find huge value and great deals on non-certified/ non-GIA certified diamonds. If you purchase one of these diamonds, make sure to have a proper appraisal respected by your insurer in case you ever need to replace your diamond.