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Diamond Certificates Explained

Q Report Team
August 05,2020 -25 min read

Shopping for a diamond can be intimidating, especially if you haven’t done it before. There’s the terminology: inclusion, cushion-cut, clarity and carat. And how can you know you’re getting what you’re paying for? On the surface, one diamond looks much like the next, even though their prices vary by thousands of dollars.

That’s why diamond certification is essential. With one easy-to-read document, you can learn everything you need to know about that sparkly stone in your jeweller’s case. And because the certification comes from a third-party laboratory, you don’t have to take the jeweller’s word for it.

In this article, we’ll go through all the information you’ll find on a diamond certificate, so next time you visit your jeweller, you can shop like a pro.


What’s a Diamond Certificate?

Independent labs evaluate diamonds according to industry standards, and they produce documents that describe various elements of the stones, such as colour, clarity, cut, carat weight, cut, cut grade, fluorescence and measurements such as the diameter of the face along with various other factors..

When you purchase a significant diamond, the jeweller should be able to provide you with a certificate, which gives you assurance about the stone’s authenticity and characteristics and above all else, clearly stating whether the stone is a natural diamond or synthetic. Trained professionals evaluate and measure the diamonds using professional tools like loupes and microscopes.

Not all diamond certifications are created equal; different labs use different formats, and their standards even vary to some degree. By learning about the labs, you will know which ones are considered the most trustworthy and mainstream.


Diamond Certification Labs

Every lab has its personality and quirks. For some time now, the most trusted diamond labs have been Gemological Institute of America (GIA) and American Gem Society (AGS). But these aren’t the only labs out there, and depending on your priorities, you may find that a different lab suits your purposes better. Let’s take a look at them more closely.


Gemological Institute of America (GIA)

The GIA produces incredibly consistent certifications, and therefore, jewellers tend to prefer it to other labs. Customers also like the peace of mind provided by a GIA certificate. 

A third-party organization like GIA doesn’t have a financial stake in the sale of diamonds. This external evaluation helps buyers to know that the gem’s stats are verified. A GIA certification provides the following information:

      • Evaluation date
      • Stone’s measurements (in millimetres)
      • Diamond shape
      • Cutting style
      • Carat weight
      • Culet size
      • Symmetry
      • Proportion diagram
      • Polish grade
      • Table percentage
      • Depth percentage
      • Girdle thickness
      • Cut grade
      • Clarity grade
      • Diamond plot showing inclusion and blemishes
      • Fluorescence grade
      • Laser inscription
      • Security features
      • Notes

The most subjective scales in diamond grading are colour and clarity. The latest developments have meant that both colour and clarity are able to be determined using technology backed by Artificial Intelligence (AI). This is cutting edge technology and will bring the consistency of diamond grading to a new sphere of accuracy.


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American Gemological Society (AGS)

Long before the GIA introduced their cut grading standards, the AGS has offered its unique cut grade scale from 0 (“ideal”) to 9 (far from ideal).

Back in the day, a diamond couldn’t be designated as “ideal” unless it could claim an AGS certificate that stated so. Now that the GIA has entered the cut grade market, though, their share in grading has fallen markedly.

Still, AGS is the go-to choice in the US, however it is not widely known or popular outside of the US. 

One issue to be aware of is “upgrade shopping.” Because colour and clarity are not objective grades (like weight and dimension), there’s some wiggle room. If a diamond falls somewhere between categories, a manufacturer or retailer may send the stone to multiple laboratories looking for a superior grade. 

For example, if a diamond is a weak H colour, or strong I colour, and they received an I grade from GIA. The wholesaler/retailer may try sending it to AGS for the H colour. If it garners a higher grading from AGS, they can sell it for more money.

Jewellers tend to use AGS for branded super ideal diamonds (like True Hearts or Hearts on Fire). You’ll find, however, that AGS is not commonly used for non-round diamonds like princess and pear cuts. So if a retailer has 25 cushion cut diamonds, 24 of which have received GIA certification and one which has an AGS certificate, the AGS diamond is likely to have received an upgrade.

Don’t perceive this to be a knock on AGS. It’s merely an observation of how some wholesalers and retailers may take advantage of the end consumer. Overall, AGS is a very reliable laboratory.


International Gemological Institute (IGI)

The IGI used to be the most popular diamond laboratory for major jewellery retailers in Canada and the United States, with limited use in Australia. You could say that it was the blue-collar workhorse of the diamond industry. They work quickly and efficiently (their prices to produce certificates are lower than those of GIA). IGI is seen as being more lenient in its grading. This means a G grading from GIA could be graded as an F by IGI. This is good for the retailer, however not so good for the consumer.

IGI may not have the prestige of some other third-party evaluators, but the certificates they produce offer plenty of helpful information for consumers.


European Gemological Laboratory (EGL)

This laboratory was severely discredited and its certificates should be avoided in general. Unfortunately, there were a number of EGL labs around the world using different standards, some excellent and very accurate and others found to be clearly overgrading and misrepresenting the quality of the stone. The consumer will not be able to tell which is the case. Hence, we suggest to stay away from stones being sold with these certificates. 


Hoge Raad voor Diamant (HRD)

Based in Antwerp, HRD was founded in 1976. Their reputation was once known to be the strictest of all laboratories. Many in the European diamond trade consider HRD to be an alternative to GIA. While they still remain to be one of the pre-eminent certificates in the world, they do not have the same exposure as GIA. 


Gem Studies Laboratory (GSL)

A laboratory run by Bill Sechos, the pre-eminent diamond grader in Australia. Certificates from this laboratory are highly regarded in Australia. The laboratory uses Sarine machines to analyse the stones. These are some of the same machines used by the GIA. 


Are Diamond Certificates and Valuations the Same Thing?

No. Diamond certificates don’t tell you how much a stone is worth under current market conditions. 

Valuations provide detailed descriptions of jewellery and ascribe a value based on specific market conditions. We provide annual revaluations to our insurance customers each year so they’ll know how much it would cost to replace their jewellery.

A diamond certificate is a laboratory report that sets out the physical specifications of a diamond’s carat weight, cut, treatment, and clarity without a judgement of value. The certificate gives you an objective way to compare diamonds while you shop.


How Can I Evaluate a Diamond’s Certificate?

When you’re shopping for a diamond, don’t hesitate to ask to see the certification for stones you’re interested in. By comparing the qualities of each diamond, you can weigh the pros and cons of each one.

After looking at a variety of gemstones, you might decide that clarity is more important to you than colour. By evaluating certificates, you can narrow down the choices that will work best for you.

It is important to discuss with your jeweller why some diamonds may have higher colour and clarity on a certificate, however do not show the same amount of brilliance than a lower colour and clarity. This has to do with the cut of the stone and the light in which it is viewed (to name just a few factors). It is important to purchase what appeals to you and not get fixated on a certificate. You look at the diamond every day, not a piece of paper. Don’t forget what’s important.


What are the 4Cs I Hear So Much About?

Anyone in the market for a diamond should learn about the 4Cs: carat, cut, clarity, and colour. These four attributes are included on diamond certificates, but not every laboratory grades them the same way. 

Because GIA grading is the most common, we’ll look at the grading scales for each attribute here.



A diamond’s carat weight measures how heavy it is. Some cuts appear to be larger than others for their carat weight. For instance, a marquise or pear-shaped diamond might have a larger surface for its carat weight than a round brilliant diamond.

A modern diamond carat equals precisely 200 milligrams (which is technically a “metric carat”). An average 1-carat diamond has a diameter of roughly 6.4mm-6.5mm, but it’s very common to see 1-carat diamonds at 6mm.



People commonly use the term “cut” to mean “shape” when they’re talking about gemstones. But when it comes to diamond certification, “cut” refers to the shape and to how well a diamond’s facets interact with the light. Precise craft and artistry result in a stone with perfect proportions and Symmetry. A diamond’s polish also contributes to its ability to interact with the light.

The GIA assigns each diamond one of the following grades for cut: Excellent (EX), Very Good (VG), Good (G), Fair (F) or Poor (P).



A diamond’s clarity refers to the absence of blemishes and inclusions. Because diamonds come from deep down beneath the surface of the earth, they often have flaws. In most cases, these flaws are apparent only when viewed through a microscope.

GIA uses six categories to sort diamonds by grade:

  • Flawless (FL) No inclusions or blemishes visible under 10x magnification
  • Internally Flawless (IF) No inclusions visible under 10x magnification
  • Very, Very Slightly Included (VVS1 and VVS2) Inclusions so small they are difficult for a skilled grader to see under 10x magnification
  • Very Slightly Included (VS1 and VS2) Inclusions observed with effort under 10x magnification but can be characterized as minor
  • Slightly Included (SI1 and SI2) Inclusions noticeable under 10x magnification
  • Included (I1, I2, and I3) Inclusions evident under 10x magnification which may affect transparency and brilliance



When it comes to diamond colour, less is definitely more. Colourless diamonds are awarded the highest marks from laboratories, and yellowish or brownish diamonds receive low grades.

GIA’s D-Z grading systems give colourless stones D grades and dark stones Z grades. In truth, most diamonds fall somewhere in between. To the untrained eye, it’s exceedingly difficult to tell the difference between some colour grades. And in the end, colour preference is mostly a matter of taste and what looks best in a particular setting.

As you can see, diamond certificates can be beneficial as you search for the perfect gemstone. If you haven’t yet started shopping, try a Q Certified Jeweller where you can purchase insurance for your piece at the point of sale.

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