The traceability and authenticity of diamonds is a hot topic and has been for decades, with numerous organisations such as the GIA going to great lengths to improve supply chain transparency for both end consumers and industry buyers.

But just how accurate are the diamond grading certificates that have become par for the course when purchasing a gemstone, asks Robins Brothers fine jewellers co-director and qualified diamond grader, Robert Robins…

Shopping for an engagement ring? You’ll need a diamond ‘certificate’. The definition of a diamond certificate? “An official document attesting a fact.”


Sounds like something you’ll want when you’re making a significant purchase right? What could be more significant than the diamond for your engagement ring? Lucky they come with certificates, right?

Wrong. They come with reports. The definition of a report? “A piece of information that is unsupported by firm evidence.”

Ok, I used the most inflammatory definition I could find, but my point is you’re being sold the idea of a 100% guarantee, when all you’re really getting is an opinion. And you know the thing about opinions…

Diamond grading certificates

Commonly and incorrectly called a certificate, the diamond grading report was introduced in 1931 by Robert M Shipley.

Shipley, a retail jeweller, set up the Gemmological Institute of America (GIA) as a non-profit organisation with the mission to “ensure public trust in gems and jewellery”.

Previous to the GIA, and its now widely known grading system of the 4Cs, diamonds were graded by letters or numbers, with no continuity between grading systems. 1955 saw the first official diamond grading report, which was soon to become the gold standard of grading reports we see today.

Following the introduction of this grading system, other laboratories appeared around the globe offering the same diamond grading services as GIA – adopting their grading system.

However, it didn’t take long for discrepancies in continuity to appear between these different labs.

Therein lies the problem. Unfortunately now it is a common occurrence to see a diamond grading report – from any of the labs – that is not accurately representing the diamond in question.

Obviously the diamonds are over-graded for colour and clarity as opposed to under-graded. Whether this is intentional or not, it is highly suspicious, and one cannot help but feel there is an unscrupulous motivation behind these misrepresentations.

Diamonds with a better grading report fetch more money. An easy and honest way to explain this away is that it is simply the opinion of the professional diamond grader issuing the report – after all, everyone can have a difference of opinion. Otherwise it’s human error. Except, some things are not up for debate.

For example, whether a diamond is ‘eye clean’ – meaning, can the inclusion be seen without the
need for 10x magnification for grading purposes, often referred to as ‘with the naked eye’?

Personally I have experienced this, but whilst I’m focusing on clarity for this example, it applies to colour and cut as well.

As carat is a measurement of weight, and not measured via human perception, but rather a scale, this cannot be easily manipulated.

As aforementioned GIA is a non-profit organisation, so the institute as a whole doesn’t stand to gain any value in over-grading diamonds, as they are only the grading body with no official biases.

Robert Robins

But the people requiring the gradings (diamond dealers) do have a profit incentive, and that’s where the system can break down.

Where there is a profit incentive, there will always be those who choose to abuse the system.

GIA is not immune to this – by proxy, in the form of its employees – however high their standards may be.

GIA was caught up in a scandal of alleged bribes, and a lawsuit that was settled at a cost of $50 million in

GIA is not the only one who has experienced problems: “HRD Antwerp has invalidated 156 diamond grading certificates and fired three employees who accepted a financial incentive for tampering with the reports at its Mumbai laboratory,” read one report.*2

Selling a diamond became easy, with no specialist knowledge required. If anything went wrong they all had a get-out-of-jail-free card in the form of a grading report.”

With all the inaccuracies I’ve seen over the years, from multiple laboratories providing diamond grading reports, it’s unlikely that it’s a one-off occurrence, or just a few bad apples.

One London-based diamond dealer who shall remain nameless asked, “Do you want a good Si2 or a bad Si2?” in response to my order. Surely an Si2 is an Si2?

It’s also widely known in the industry to stay away from certain laboratories that are blatant in their over-grading, but also to stay away from particular GIA grading reports from certain locations.

But the opposite is also true. If you want a “certain grade on a certain diamond, you submit it to a certain lab”, said Donald A Palmieri, president of the Gem Certification and Assurance lab.*3

This conundrum not only applies to clarity, but also colour and cut. How can anyone trust a diamond if they don’t have the training or knowledge required to accurately grade the diamond themselves? This goes for buyers within the industry as well as retail customers.

So what is the problem?

For decades diamond grading reports offered a reliable and trustworthy way for untrained consumers within the industry or customers on the high street to buy diamonds.

They could be assured that the grading report was accurate and representative of the stone they were
purchasing – not only a diamond, but also graded according to the 4Cs.

The introduction of these grading reports created a lack of emphasis on sales staff requiring specialist training.

Anyone who can read a diamond grading report can sell a diamond with no real knowledge of how a diamond is graded, or even how the difference in grades affects price, let alone check the report’s accuracy.

The popularity and reliance on diamond grading reports gave way to a swathe of internet shops, selling diamonds by their grading reports, and high street jewellers leaning on the reputation of GIA and other labs, to instill buying confidence for their customers.

Selling a diamond became easy, with no specialist knowledge required. If anything went wrong they all had a get-out-of-jail-free card in the form of a grading report.

Ultimately it is the unsuspecting public who are the victims here. They buy the certificate and not the diamond, comparing certificates instead of seeing diamonds in-person and up close.

There are an abundance of factors that affect a diamond’s optical properties, not just colour, clarity and
cut – all of which affect price, none of which can be seen by comparing certificates.

Retailers on the high street will have you think that, like for like, their diamond is cheaper.

Knowingly or unknowingly to them, the cheaper diamond will be of a lesser quality than its comparative
more expensive diamond.

That isn’t always the case, but more investigation is needed than simply reading a grading report for comparison.

Some apparent acknowledgement of this problem was highlighted in September 2020, the international standard organisation specified terminology and classification when it comes to grading loose diamonds.

However, this isn’t yet law, and is still voluntary. The ISO said, “Some diamond-grading reports may be issued based on different standards by different laboratories, potentially leading to different results for the same individual diamond.

“This situation damages the reputation of the whole diamond trade. Hence the need for a unique ISO standard for grading polished diamonds.”*4

There are, however, a very small number of traditional jewellers and boutiques that do possess such specialist knowledge.

If you’re within the industry there are many courses you can take to brush up on diamond knowledge.”

These jewellers put their personal reputations and livelihoods on the line to ensure they are selling a diamond that matches its grading report; they can spot an inaccurate report and return it for an accurate one so that their customer is paying the right price for the right diamond.

After 20 years of experiencing these problems first hand, I do have some advice: if you’re a retail customer and want to buy a diamond, find someone you can trust, a jeweller who has a good reputation among friends, family, independent reviews or even the local community.

Check their credentials. Time served isn’t always a good indicator of experience or knowledge. They should have some education in diamond grading, or valuing, at a firm which shows understanding of the 4Cs and a wider understanding of diamonds and the industry.

If you’re within the industry there are many courses you can take to brush up on diamond knowledge.

GIA runs the most in depth course and has multiple locations to study from, or there are shorter courses run by Anchor Cert in the UK.

Knowledge is power, and if you want to be sure you’re providing the best service you can to your customers, then diamond education is paramount.

The problem with diamond grading reports isn’t really a problem at all – if you follow my advice, you can be sure you are buying, or selling, in confidence.

Words by Robert Robins

*1 – NY Times Reports GIA Scandal, Suit in Settlement Negotiations (

*2 – HRD Uncovers Tampered Diamond Grading Reports


*4 – Diamond Grading Gets an International Standard