Yes. The 5th C refers to Certificate. The diamond certification (also known as a grading report) is a document that contains vital information on the diamond’s properties, such as the 4Cs, fluorescence, and other remarks.
Untrustworthy jewellers will frequently dismiss this document by saying things like “it’s just a piece of paper” or “you’re buying the diamond, not the paper.” A certificate from a reputable, independent third-party lab, such as GIA, gives you peace of mind and guarantees the diamond’s quality.
This 5th C of diamond shopping confirms the veracity of the 4Cs. If a certificate’s source is untrustworthy and uses dubious grading standards, the diamond’s quality may be overstated.