Two famous labs, one big decision – here is how to choose with confidence.
Short answer: IGI and GIA are two of the world’s most trusted independent diamond laboratories. A grading report from either one tells you exactly what you are buying – carat, colour, clarity and cut – and lets you check the diamond online. GIA is often preferred for large natural diamonds; IGI is the most common choice for lab-grown diamonds and finished jewellery.
- A certificate (grading report) describes one specific diamond: carat, colour, clarity and cut.
- GIA is often preferred for large natural diamonds; IGI is the norm for lab-grown diamonds and fine jewellery.
- Always check the report number on the laboratory’s own website.
- Every John Gems N Jewels® diamond is IGI or GIA certified; pieces over 1 carat come with their own certificate.
What a diamond certificate is
A diamond certificate – more correctly a grading report – is a document from an independent laboratory that describes one specific diamond. It is not a price tag and not a guarantee of value; it is a precise description, measured by gemmologists with professional equipment. A good report lists:
- the 4Cs: carat weight, colour, clarity and cut;
- the exact measurements and proportions;
- polish, symmetry and fluorescence;
- whether the diamond is natural or lab-grown, and any treatments;
- a unique report number, often laser-inscribed on the diamond itself.
IGI and GIA at a glance
| GIA | IGI | |
|---|---|---|
| Who they are | Gemological Institute of America, the non-profit that created the 4Cs grading system | International Gemological Institute, one of the largest laboratories in the world |
| Known for | Very strict, consistent grading of natural diamonds | Lab-grown diamonds, finished jewellery and detailed cut reports |
| Often chosen for | Large natural diamonds and engagement stones | Lab-grown diamonds and set jewellery |
| Check online at | gia.edu (Report Check) | igi.org (Verify Your Report) |
Because the two laboratories calibrate slightly differently, the same diamond can occasionally receive a grade one step apart. That is normal. What matters is that you compare like with like, and that the report matches your diamond.
How to read a certificate in five steps
- Find the report number at the top of the document.
- Check carat weight – to two decimal places, for example 1.01 ct.
- Look at colour and clarity – colour runs from D (colourless) downwards; clarity from FL (flawless) through VVS, VS and SI.
- Read the cut, polish and symmetry – “Excellent” or “Ideal” means the diamond returns the most light.
- Verify it online on the laboratory’s own website using the report number.
Which certificate should you choose?
For most buyers the honest answer is: choose the diamond, then make sure it has a report from a respected independent laboratory. A beautifully cut diamond with good colour and clarity is beautiful whichever laboratory graded it. If you are buying a large natural stone mainly as an investment, many buyers prefer GIA; for lab-grown diamonds and fine jewellery, IGI is the industry norm.
Certified diamonds at John Gems N Jewels®
Every diamond and every piece of diamond jewellery we sell is IGI or GIA certified, and every piece over 1 carat comes with its own IGI or GIA certificate. Because many of our pieces are made to order, the certificate belongs to the exact diamond set in your piece and is supplied with it.
From our collection
Frequently asked questions
Is an IGI certificate as good as a GIA certificate?
Both are respected international laboratories. GIA is often seen as the strictest for natural diamonds, while IGI is the most widely used laboratory for lab-grown diamonds and finished jewellery. What matters most is that the report comes from an independent laboratory and matches your diamond.
How do I check a diamond certificate?
Enter the report number on the laboratory’s own website (igi.org or gia.edu). The details shown online must match the paper report and, if the diamond has one, the laser inscription on its girdle.
Does a certificate change how a diamond looks?
No. A certificate describes the diamond; it does not change it. Two well-cut diamonds with the same grades look the same whichever laboratory graded them.
Do John Gems N Jewels® diamonds come with a certificate?
Yes. All our diamonds and diamond jewellery are IGI or GIA certified, and every piece over 1 carat comes with its own IGI or GIA certificate.
