Diamond Guide
Never buy a diamond without one. Here is how to read a grading report, and which four lines on it actually decide the price.
Every diamond we sell comes with one of these. It is issued by an independent lab, not by us, and it is your proof of exactly what you are buying.
Diamond Grading Report
Report no. 2416 •••• · laser inscribed on the girdle
The four highlighted lines are the 4 C's. They decide most of what you pay.
The jeweller is not the one grading the diamond. Standard grading reports are issued by agencies around the world, and some are far more reliable than others. GIA (Gemological Institute of America) and IGI (International Gemological Institute) are currently the two you can trust.
It matters that you have a jeweller who will sit down and review that grade with you under 10x magnification. Small differences in what is ultimately a subjective assessment can move the price by 5 to 20 percent.
A diamond may be graded SI2 but on closer inspection could reasonably be argued as SI1, and that is a meaningful difference in price. Grading happens at the margins, and the margins are where you save.
A certificate is also called a diamond quality document or a grading report. Before buying, always expect to see a copy as proof the stone underwent professional examination.
We can navigate all of this with you, so you know exactly what you are investing in.
Before the middle of the twentieth century there was no standard for assessing diamond quality. Then came the system every report in the world now uses.
How white the stone is, or how little colour it holds. Graded D, colourless, through to Z.
The presence and visibility of the tiny natural inclusions formed as the diamond grew.
How well the stone was cut. This is the grade that decides brilliance and sparkle.
The weight of the stone. One carat is 0.2 grams, and price climbs exponentially.
The two most respected grading laboratories in the world. Here is what makes each trusted, and which to look for depending on the stone.
Gemological Institute of America
Widely considered the gold standard in diamond grading. Their standards are the most stringent and the most consistent in the world, which is why a GIA grade holds its value in any market.
International Gemological Institute
The most widely used lab for grading lab-grown diamonds. Reliable, universally accepted, and their reports are comprehensive. For a lab-grown stone, IGI certification is entirely appropriate.
Five things worth confirming on any report you are handed, whoever you are buying from.
Any other name on the report should give you pause. Standards vary enormously and an inflated grade is the most common way buyers overpay.
Most certified diamonds carry a laser inscription on the girdle. It should match the report exactly. We check this with you under magnification.
Cut is the only grade you can genuinely see across a room. Do not let a strong colour or clarity number distract from a mediocre cut.
A report tells you the grade. It does not tell you where an inclusion sits, and position matters more than the letters do.
Grading standards shift over the years. An older report on a resale stone is worth re-checking before you commit to a price.
Strong fluorescence can make a stone look hazy in daylight. It can also be a bargain if it does not. Either way you should know.
Never purchase a diamond without a certificate from one of these two labs. Any other certification should be viewed with caution, because the standards vary significantly and the grade may not be reliable.