Why the certificate matters more than the seller
A grading report from an independent laboratory — GIA or IGI are the global standards — is the only objective description of your diamond. It is what makes two stones comparable across sellers, what your insurance values, and what protects you from paying a G-color price for a J-color stone. Never buy a significant diamond, mined or lab-grown, without one.
The headline numbers: the 4Cs section
Carat weight is measured to two decimals. Color is a letter (D–Z); clarity a grade from FL to I3; cut (for rounds) a scale from Excellent to Poor. Check that the certificate's numbers match what the listing claims — exactly, not approximately. For lab-grown stones the report will state 'Laboratory-Grown' prominently and usually notes the growth method (CVD or HPHT) and any post-growth treatment.
The fine print that experts read first
Fluorescence: 'None' to 'Very Strong' — faint-to-medium is harmless and can even make a lower color look whiter; strong fluorescence in high colors can cause haziness and trades at a discount. Proportions: for rounds, a table of 54–60% and depth of 59–63% sit in the sweet spot. The clarity plot — the little diagram of inclusions — tells you where the flaws are: inclusions under the table are more visible than ones near the girdle that a prong will cover.
Comments and red flags
Read the comments line. 'Clarity grade based on clouds not shown' on an SI stone can mean a hazy, sleepy diamond despite a clean-looking plot. 'Laser drill holes' or 'fracture filled' mean the stone was treated and should be priced far lower. On the seller side, be wary of certificates from unknown labs with implausibly generous grades — a stone graded two color and two clarity grades higher than GIA would grade it is not a bargain, it is mislabeled.
Verify before you pay
Every GIA report can be checked at report-check on gia.edu and every IGI report at igi.org/verify — type the report number and confirm the details match the paper and the stone. Most certified stones also carry a microscopic laser inscription of the report number on the girdle, which a jeweler can show you under magnification. At Starla, the certificate details for your center stone are recorded in your order's product specification, so the paper trail lives with the order.