Lab-Grown Diamond Certification: IGI, GIA and What to Check

A certificate is what separates a graded stone from a promise. Here is how to use one properly.

Which labs to trust

IGI and GIA dominate lab-grown grading, with IGI the most common for lab-grown goods. Both grade to the same 4Cs standard. A certificate from an unknown 'in-house lab' is not a certificate in any useful sense.

The lines that matter

• Measurements — millimetres, not just carat. This tells you the face-up size.
• Cut grade — excellent/very good/good. The most important line on the report.
• Colour and clarity — D–F and VS/VVS are the ranges worth buying.
• Polish and symmetry — both should be excellent or very good.
• Fluorescence — none or faint is ideal.

Verify the number

Every report has a number you can check on the laboratory's own website. Do it before you buy — it takes 30 seconds and confirms the stone matches the paper.

Growth method

IGI reports state whether the stone is CVD or HPHT. As explained in CVD vs HPHT, this matters less than the grades.