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A Comparison of Diamond Certification Laboratories <The Ultimate Diamond Buying Guide>

*Do note that our writings are based on our personal opinion and only serves as a reference or guide.

In this article, we will give a comparison on gemological labs and grading certification in the market and which are the ones you should avoid based on certain specific criteria.

Until the middle of the twentieth century, there was no agreed-upon standard by which Diamonds could be judged. The Gemological Institute of America (GIA) created the first, and now globally accepted standard for describing Diamonds: Color, Clarity, Cut and Carat Weight. A Diamond’s 4 C’s are the main components that makes Diamond so attractive to our eyes. The creation of the Diamond 4 C’s meant two very important things: Diamond quality could be communicated in a universal language, and Diamond customers could now know exactly what they were about to purchase.

Diamond grading laboratories are supposed to be third party neutral organisations that serve to give an opinion on what the grade of the diamond is. GIA and AGS (American Gem Society) are known as the most trustworthy due to their high standards of grading.

And this is important because...

As a consumer, the certificate will let you know what exactly you are buying which then lets you justify if you are paying the right price. Hence, buying a diamond that has a certificate from the right third party neutral organisation will prevent any conflict of interest or biases.

Personally I would not buy diamonds that come in any other certificates other than GIA or AGS, unless they are small sizes and in bulk that I would use as decorative designs rather than the centerpiece.

Laboratories in the Market

Different laboratories have different grading systems and standards. Hence a report from one laboratory may have 2 or even 3 grades difference compared to the report issued by another laboratory for the exact same diamond.

This is important because dealers and retailers based the grading standards (therefore prices) on GIA's standards of grading. A certificate from another laboratory that deviates from GIA would then affect the value and the price you would be paying for a diamond. If you based your purchase solely on the grades of a certificate without understanding, very likely you will be overpaying for a diamond with a lower qualities.

For example GIA would consistently grade a certain type of diamond G SI1. However another laboratory may grade these diamonds E VS1. There might be instances where you pay for a E VS1 GIA price instead when its only worth a G SI1 GIA price. This will be explained below in the EGL section.

There are four main popular laboratories in the world that grades diamonds: GIA, AGS, EGL and IGI. Each of them has their own way of describing diamonds and may use different matrices.

GIA is the most trusted and widely used service. They are highly recognized for the extremely strict grading standards and their consistency.

In the GIA laboratory each diamond is graded independently by two diamond graders, and if their grading standards do not match, a senior grader would have to provide another opinion. This is in comparison with many other laboratories whereby a diamond only grades through one grader which has more room for mistakes or biases.

For coloured diamonds, GIA standards are even more so strict. We once wanted to send a 10ct deep brown diamond for grading but GIA would only grade that diamond in their headquarters in Carlsbad. Insured shipping would come up to 2,000 dollars. While they do grade coloured diamonds in very specific offices like the one in Tokyo, they only do so for coloured diamonds below 5 cts. Coloured diamond graders need to achieve a certain milestone in their careers to be qualified for it, hence GIA only have this service in very specific countries.

When we buy diamonds from B2B, we would usually only rely on GIA or at most AGS if it is a 'Ideal' or modified cut. If you were to buy an diamond with a GIA report, rest assured that it will provide you with the greatest peace of mind that its quality is represented accurately.


  • GIA does not give a cut grade for Modified Cut Diamonds

  • GIA's maximun grade for Cut is the grade 'Excellent'. This ensures that your diamond will look decent, but does not guarantee it will be the best, unless it falls in the red box drawn in the chart.

So in this chart, given certain cutting proportions, we can see that diamonds that fall in the dark blue center will be given the cut grade E, which means Excellent. However there is also a wide range of Excellent diamonds, which about 3% of diamonds graded by GIA will qualify as.

Hence a competing laboratory AGS, created their own grading scale that scrutinizes diamonds even more and created the Cut Grade 'Ideal' which in their scale is better than 'Excellent' which makes up of only 1% of the diamonds graded by AGS (not GIA), diamonds that are very likely in the red box.

*Red box drawn is for depiction purposes only to show that 'Excellent' cut diamonds come in a wide range. The closer the diamond is to the center box, the more brilliant the diamond will be.

But do note that there are overlaps in the grading systems, such as the AGS Excellent Diamond can be graded as a GIA Very Good. I will include an approximate reference chart for these 2 laboratories at the AGS section.

All in all, I would recommend GIA as the first choice of certification. GIA is also a leading educational provider in the the industry and frequently publishes interesting technological developments and discoveries in the gemological world.

*GIA is an amazing laboratory for diamonds and coloured diamonds, but is not our first choice for coloured gemstones (Ruby, Sapphire etc).

AGS is the second most widely used laboratory after GIA. Their standards and grading consistency is also known to be good. Instead of using the alphabetical grading system, AGS uses a number scale which can be quite confusing to some people.

However, their system can be easily convertible to GIA's system for Colour and Clarity grading. There is only some overlaps for Cut grading which is why we have included an approximate Cut conversion chart based on data and our experience in the market that just serves to give you an idea.

Like I have mentioned above, AGS created their 'Ideal' cut standard which is picks out better the better cut diamonds from the GIA Excellent bunch. Hence certain diamonds may be sent to AGS instead if it is suspected to be an 'Ideal'.

But also be very wary of marketing terms used. Some retailers may calls their diamond Super Ideal, Perfect Ideal etc., but it is important to do your due diligence and check the official grading on the AGS certificate, rather than rely on in-house printed certificates.

AGS Add-Ons:

  • One interesting thing that AGS did was they included a chart of the diamond's light performance, which you can see in the certificate below as the glaring red circle. It works similar to the ASET Light Return Scope.

Do Note:

Here you can see how the AGS diamond certificate actually includes the AGS vs GIA conversions. However, there is No Conversions for Cut Grading.

So this is why we included it in our chart above but do bear in mind that it is only an approximate based on the data we have collected and our market knowledge.

It is not definitive but it serves as a guide.

In our opinion, unless you only want an 'Ideal' diamond, I would always recommend diamonds with GIA certificates instead.

They are just a lot more convenient to trade in the international market and GIA is the basis of standards.

They are known for having the SI3 clarity grade, which is a very close grade from Industrial Grade diamonds. I would never recommend buying an SI diamond if possible as they usually come with black crystals and have durability issues.

And as mentioned above, I would only deal with certificates from GIA or AGS. If you were to buy a diamond that comes with this laboratory, there are times where a huge discount may be given. However there are cases, that the grades written on the certificate deviates far from GIA/AGS standards.

Hence sometimes, it may seem that you are getting a way better deal for a diamond that has the same paper grading that is certified by EGL. But there are instances that the diamond when sent to GIA, may come up with a diamond of lower grading.

There have been cases where an EGL certificate comes up to be 2-3 grades better than the GIA gradings. For example, EGL VS2 diamond would be an actual GIA SI2, or the colours would also have 2-3 grades different. Remember how prices are based on GIA's grading?

For example, (numbers are figurative)

Price of GIA D VS2= 1000

Price of EGL D VS2= GIA D VS2 - 20% Retail Discount

= 1000 - 200

= 800

If sent for regrading and the EGL D VS2 diamond turns out to be a GIA D SI2:

Price of GIA D SI2 = 500

But you have paid 800. In this case you paid 300 more for a diamond which actually had a lower grading based on GIA's standards, which is the international standards. If there was no retail discount given, you would have paid even more. Retail discounts are often given to diamonds that are not certified by GIA or AGS as most retailers would have accounted for the grading deviations from GIA.

A huge scandal on EGL's grading standards came up in 2014, which led to the decision of the Rapaport Group to de-list all EGL reports from RapNet.

In a nutshell, as taken from the article:

'In his report, Mr. Rapaport blasted the EGL for utilizing Gemological Institute of America (GIA) diamond grading terminology but not GIA grading standards. He explained that this results in overgrading and misrepresentation.'

'Overgrading, as he defined it, has occurred when a diamond graded using GIA terminology proves to be more than one color grade or one clarity grade lower than the original grade when verified by the GIA. He backed the GIA’s diamond grading language and standards as employed by the entire industry.'

The GIA is the global diamond grading standard accepted by the international trade and the legal systems of the United States and other countries.

However, EGL in the scandal argued that 'there is no single, international standard for diamond grading that has national or international status or acceptance... that the results of diamond grading are, to a certain extent, subjective.'

This means that they EGL felt that they grade diamonds based on their own grading system and is not 'overgrading' as what was suggested. However, this claim was refuted by Rapaport who questioned if EGL does not recognise GIA's grading system, why does their grading system 'employs all aspects of GIA’s terminology when describing color, clarity, cut, and carat.'

And 'if the industry accepts this claim of no grading standards. He stated the demise of the globally accepted GIA grading standard, the language of the trade, would result in the collapse of diamond prices, since dealers, retailers, and consumers would no longer have a benchmark for differentiating quality and price.'

According to Rapaport, the catastrophic consequences of diamond overgrading extend beyond fraudulent transactions. Read the full article here to have a better understanding.

Similar to EGL, personally I would not purchase diamonds with this certificate too. Or if I have to, I would be more cautious. There are also times where IGI has reported to give 2-3 grades better than GIA/AGS.

However, we have also heard of some companies who choose to send their stones to IGI instead to attain a better grade on paper. Many consumers have paid much more for an IGI graded diamond thinking they actually had good deal. Do remember that most diamond prices are based on GIA's standards. So if you convert it to GIA's grading, how much would your diamond now be worth?

I would just say, buy at your own risk. Many customers who seek regrading at GIA or AGS have reported receiving discrepancies in their certificates.

In-House Laboratories

Firstly there may be a conflict of interest, compared to using GIA/AGS who provides neutral third-party opinion. Remember how a certificate is a testament to a diamond's quality and hence value. This also applies to international brands, who may charge a premium, but may not always be offering the best diamonds based on GIA's standards.

From our experiences, some boutiques may say that their in-house diamond graders are from GIA, and hence the standards are the same. This is a vague statement that could mean that either their in-house graders used to work for GIA as graders or they have only taken a course from GIA. Read my article here to understand how the latter, Professional Diamond Graders come about. In essence, it is quite an easy process with 2 weeks of learning if you are fast. But this experience level is different from being a GIA diamond grader - those that work in GIA, not merely taken a course from GIA.

In explaining:

I could say that I am a GIA Gemologist, but this is not the exact term for it. A GIA Gemologist works for GIA as a Gemologist. However, I am a Gemologist who was merely accredited by GIA, meaning to say, graduated for GIA. That is the difference in the terminology that may cause confusion in customers by saying that a certain organisation are or have GIA Diamond Graders.

If you read till here, I'll share with you an interesting discovery...

So a while back I was at SK Jewellery looking at their Celestia diamonds at Nex Shopping Center. The sales staff explained that this range of Celestia diamonds, was a selected range of standard cut diamonds that were cheaper, with lower colour, clarity and cut.

Interestingly, a competitor Goldheart launched their Celestial Diamonds earlier. The names were pretty confusing for me, Goldheart's launch has an extra L at the back. Goldheart Celestial vs SK Jewellery Celestia. The difference is that Goldheart's Celestial is a range of diamonds that has a starburst effect from its modified cutting and of course this trademark is sold at a premium. On the other hand, SK Jewellery launched Celestia that is a lower cheaper range of standard cut diamonds. In my opinion, this is quite a surprising competition strategy.

But back to certifications which is the main topic of this article, I later asked the SK Jewellery sales staff if these Celestia diamonds comes with certification. She replied yes and showed me the certificate from Institute of Advanced Gemology, and told me that it was a renowned laboratory in Asia.

In my experience in the trade, it is the first time I have heard of this laboratory. I might have known some less famous laboratories in Hong Kong, Japan, Thailand, but this was the first. Being curious, I studied the Institute of Advanced Gemology certificate properly and realised their business address is in Singapore.

Here is a sample certificate is taken from the official IAG website. I did not manage to take a picture in the shop back then.

That night I went home to do more research and found a report on their business profile..

"INSTITUTION OF ADVANCED GEMOLOGY PTE. LTD. (the "Business") is a Private Company Limited by Shares, incorporated on 1 September 2011 (Thursday) in Singapore. The address of the Business's registered office is at the SOOKEE HQ building. The Business current operating status is live and has been operating for 8 years 218 days. The Business's principal activity is manufacture of jewellery except costume jewellery." - taken from

It is known that SK Jewellery is under Sookee Group. The IAG laboratory however, is quite a coincidence. I was not expecting this. Is it possible that IAG is just leasing a space? The information is available online, if you would like more information, please search on the relevant web pages.

While we do not compete in the diamond space we cherish and loved the industry. We believe in making it better for everyone by sharing our knowledge, experiences and findings.

In a nutshell, remember that a diamond certificate should be a neutral testament to a diamond's quality based on international standards (GIA's standard) because that directly affects the price you would be paying for.

Head back to our Ultimate Diamond Buying Guide to learn about the other components of diamond grading.


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