Diamond Certification: Which is Best Grading Lab for You?

Diamond Certification: Which is Best Grading Lab for You?

Diamond Certification: Which is Best Grading Lab for You?

Posted by Sharif Khan on 27th Dec 2020

Diamond Certification and Grading Guide

The price you pay for a diamond by and large depends upon how the diamond is graded in the grading report and/or the "certificate”.

The reports of the Gemological Institute of America (GIA), HRD Lab, American Gem Society(AGS), and Gem Certification and Assurance Lab (GCAL) command the highest premium in the industry. However, among all the other gem labs, there is significant discrepancy in how they grade diamonds and in the reliability of their grading reports.

Please review our comments below about the difference between AGS vs GIA and where one may have an edge over the other. Overall, the GIA is still considered the standard-bearer in the industry when it comes to educating customers about diamonds. They are also the most consistent at grading diamonds. Here are our notes on IGI vs GIA for your review.

Please check out James Allen's 3D 360 degree image technology for assessing the cut of GIA graded diamonds.

Please carefully review our comments in the graph below as we have tried to summarize every important aspect about each lab to save you time. 

Key takeaways:

In this article, we have shed light upon the various certifications and grading systems that different diamond grading labs offer, the ways in which they do so, their cons, and the key factors that you need to consider while buying a stone. Herein, we have also tried to elaborate on the reasons why certain jewelers/dealers will try to coerce you into believing that grading is not necessary and that you will be better off without it; a hoax that you must not believe. We hope that owing to these details and those discussed in the rest of our articles, you will be able to make a better, more informed decision.

Diamond Certification Ranking

Below, is a brief video presented by Sharif explaining the various labs:

In short, diamond certification is extremely important. Do not buy a loose diamond that is not graded by a reputable lab. Local jewelers will put forth various reasons before you to justify that a grading report is not necessary and will convince you to buy a stone that is not graded by a reputable lab. If they succeed in selling you a one grade of a diamond, they will make a lot more money in the process. This is so because they profit by selling you a loose diamond with no certification or one that is graded by a lab that is lax in their grading criteria.

A reputable diamond dealer will always send their stones to the GIA for grading because they are confident in the quality of their diamonds, knowing that they are exactly what a customer would look for. As for not sending their stones to the GIA, the only reason why such dealers would do so is because they think that other labs will give them better grading results than the GIA.

We know that the GIA is extremely strict and professional in grading diamonds. The only factor that you have to look for is the cut in GIA reports. They offer a cut grade only in round cuts and not in other shapes. This proposition can be remedied by following our guidelines on ideal proportions for each shape that will not let you go wrong with a GIA graded diamond for as long as you stick to them—the guidelines, so to contend. It may be helpful to verify a GIA report here.

The AGS is a reputable lab but can at times be inconsistent in grading clarity and color properly, even though these are minor issues at best. However, they excel in grading the cut of diamonds because they use a proportion-based system.

The IGI is a decent lab but not as good as the GIA or the AGS. We wouldn't worry about them if we were buying a lower color grade (I-J-K) and high clarity (VS/ VVS) diamond.

The GCAL is a great lab but has a small market share. They are on par with GIA to a large degree. Therefore, if you see a GCAL graded diamond, do not hesitate to purchase it. Ideally, a diamond will come with both a GIA and GCAL report.

An Illustration of GIA Excellent Cut vs AGS Ideal Cut Diamond: (Click on each image to watch a 3D Video of Each Diamond)

James Allen Brian Gavin Diamonds

If you are shopping for high quality AGS graded ideal cut diamonds, check out Whiteflash. They have the best selections for AGS graded diamonds.

On certain occasions, you may get conflicting opinions because gemologists will tailor their opinions to the lab that might have graded their diamonds so as to be able to make sales. These opinions are definitely biased, and so you should be cautious of them while shopping for diamonds. Please follow our in-depth diamond guides for shapes of diamonds so you can make informed judgments when buying diamonds.

The diamond trade has evolved significantly over the past decade. Now, almost everyone works with the same set of dealers and can act as an intermediary between you and the dealer.

What are the Top Diamond Certifications in the World?

We highly recommend GIA as the top lab and consider AGS, HRD, and GCAL as reliable labs. The International Gemological Institute (IGI) is also improving its process of grading diamonds. Unfortunately, The European Gemological Laboratory (EGL) has lost much of its credibility and market share. The Gemological Science International (GSI) is an adequate lab but one that will, at times, have one or two grade inconsistencies. The Professional Gem Science Laboratory (PGS) is also a dependable lab but does not enjoy a significant market share. Moreover, the GCAL is also a very reputable lab, though it too has a small market share.

GIA Certification

The Gemological Institute of America is a non-profit organization dedicated to researching, and educating consumers, about jewelry and gems. They study and grade all types of gemstones. In addition to the lab services, the GIA also trains gemologists and offers in-depth education and research support for the diamond industry. Presently, the GIA’s diamond grading reports are the top-rated diamond “certification” and verification documents in the industry.

The GIA offers two types of diamond grading reports: full reports and diamond dossiers for small diamonds. The dossiers are less expensive as opposed to the full reports and do not include the full plot of the diamond responsible for showing the exact location of inclusions in a diamond. Because the locations of inclusions are not determined in dossier reports, the GIA will require a mandatory laser inscription of the diamond. This, however, is not the case with full reports. Diamond dealers can buy the laser inscription as an added service for $30, though it is not a requirement.


There are discussions on how the GIA determines excellent cuts in diamonds. One issue, among others, with their grading is believed to be their broad criteria when assigning excellent cut grades to diamonds; excellent cut grades being the highest in the GIA’s scale. It has been suggested that because the AGS uses a proportion-based system for assigning ideal cut grades in their reports, its grading is superior to that of the GIA. Please look up diamond proportions and read our detailed report on this matter for a greater understanding.

AGSL - AGS Certification

The American Gem Society is a membership organization of jewelers, suppliers, appraisers, and traders. The company has been in operation since 1934; however, its laboratories—the American Gem Society Laboratories (AGSL)—were founded in 1996. They also have an advanced instruments division founded in 2004. The AGSL is the division that grades diamonds and has developed their own standards for doing so. It is a close competitor to the GIA having a strong reputation in the diamond industry.


When it comes to grading a diamond's clarity, the AGSL will not be consistent at times. We have noticed such diamonds in the SI2 range graded by it about which we can confidently say that the GIA would not assign SI2 grades to. So, when it comes to clarity grading in the SI1/SI2 range, be wary of the AGSL's inconsistencies.

HRD Certification

HRD Antwerp is mainly owned by the Antwerp World Diamond Center founded in 1973 which represents the Belgian diamond industry. As you might know, Antwerp is one of the main centers for diamond trading and supply. The HRD Lab’s standards are similar to the ones used by the GIA. They also follow grading rules set by the International Diamond Council and are extremely reliable.


Please note that we normally assume that there would be a grade inconsistency in HRD's grading when it comes to the grading of diamond color - please bear this in mind that as you consider buying HRD graded diamonds. Also, they can be inconsistent when they grade diamonds for clarity.

IGI Certification

The International Gemological Institute was established in 1975 and is headquartered in Antwerp—one of the key centers for the diamond industry. The IGI has several branches worldwide, is one of the largest labs in the world, and also has a gemology school. Owing to the fact that the IGI is extremely large spanning across the world, their labs in different countries seem to use slightly different criteria while grading diamonds which practice causes overall grading inconsistencies. However, they are improving their overall performance. We would grade the IGI as slightly less strict than the GIA or the AGS. You can expect one grade inconsistency while buying IGI diamonds. However, no two diamonds are identical, and so generalizing anything when it comes to buying diamonds is not a good idea—because each case is different, it ought to be treated differently.


You can expect one grading inconsistency in the overall grading process when it comes to IGI's grading in all four Cs.

GSI Certification

Gemological Science International mainly grades diamonds for some large chain stores in mass numbers. Recently, they have expanded their operations to a number of countries worldwide. The GSI is a favorite choice of large stores because they grade diamonds much faster than GIA or AGS. It is close to the IGI in grading diamonds and usually grades diamonds one grade lower than the GIA or the AGS. Again, as it has already been stated, because each diamond will have its own characteristics, it is important that diamonds are considered individually. (The insights that are offered are good for general information purposes.) However, if you are not well-informed or if you do not have the time to learn about diamonds, then go for either the GIA or the AGS.


It is wise to be cautious when evaluating GSI's diamonds. Expect a grade inconsistency and make sure you run the stone by an expert and get a third party opinion. The sad part is that most appraisers are unreliable, and so you will most likely be indulging in a trade-off when buying GSI graded diamonds.

EGL Certification

The European Gemological Laboratory used to have significant shares in the diamond grading business; however, it has lost the lion’s share of the credibility it once exercised. They are reorganizing the organization, and, at least for the time being, you should not rely solely on their reports. As a result of their decrementing reputation, even RapNet does not allow EGL graded diamonds to be listed on its platform.


It is a safe bet to avoid EGL graded diamonds unless they are from the era of 1950s to early 2000s - and even in these, you can expect up to two grade inconsistencies in the overall grading.

How are Diamonds Certified?

In order for you to make an informed decision on the various diamond grading reports/certifications, it is important to understand exactly how diamonds are graded in the first place. The major gem labs have remarkably similar processes for analyzing and grading diamonds. The process usually involves several graduate gemologists independently assessing the cut, color, clarity, and carat weight of the diamonds with the final grades being extracted after all the assessments have been evaluated. The process helps to reduce the potential for human error in the determination of a diamond’s final grade, but it still does not eliminate it. Grading labs have been known to give different grades to diamonds that are sent to them for the second time; this difference is more noticeable when multiple diamond certification labs are involved in the overall process.

Diamonds are not certified; no lab would say that they are "certifying" diamonds. Legally speaking, it can cause them trouble, and so all they will say is that they grade diamonds based on their best judgments.

Consistency of result:

Part of the reason behind the AGS and the GIA’s dominance is their consistency; in that they are able to consistently assign similar diamonds the same grades. If you were to send a diamond to the two major labs for evaluation, you would probably receive certificates without any grading differences or only with minor differing grades that are generally accepted in the industry. However, when a single lab’s own evaluation disagrees, it’s considered a sign of careless work.

Certificate Standards:

Another major consideration for diamond certification are the certification standards according to which various labs operate. In illustrating this point, one could consider the GIA and the IGI side by side: the former is a non-profit organization while the latter a commercial institution. As is expected, the GIA is known to be more objective than the IGI when grading diamonds simply because the latter is bound by their profit motive to be more customer-oriented; the customers, in this case, will be diamond merchants. This disparity in results is an open secret in the industry. Sometimes, commercial labs would give diamonds a one point higher grading on average than that given by the GIA and the AGS only to make its clients happy. But, as a buyer, it may mean something for you.

You may find two diamonds with similar grades from the IGI and the GIA, with the one from the former having a lower price tag than the one from the latter. It seems like a bargain to purchase the diamond with the lower price; but if you spend money buying the diamond graded by GIA who gave it a lower grading than the IGI, it will be sold for a lower price.

Principally, from a buyer’s perspective, a diamond certification is critical when buying a diamond. The diamond grading or certification comes from a wide variety of labs. Diamonds are graded with varying reliability, but to get the best deal, you should purchase a diamond that has either been certified by the GIA or the AGS.

More Details on GIA and AGS Grading Systems

The GIA Diamond Cut Grading System

The most important innovation in the diamond industry in the 1950s is, undoubtedly, the GIA’s cut grading system introduced to serve as the standard for which all gemstones and diamonds are specifically judged. Although the 4 Cs of diamond grading were already well known and there were a number of other grading systems in use, it became necessary to have a uniform grading system to promote consistency across the industry. Today, the GIA cut grading system is the most widely used and accepted grading system for diamond cuts.

The key features of a diamond that the system considers when assigning a grade are: color; clarity and make, comprising of the cut, polish and finish. There are five grades a diamond may be assigned after being evaluated by the GIA:

Excellent Grade – Diamonds with this grade will have an even pattern of light and dark areas when one looks at the stone as well as high brilliance and scintillation.

Very good Grade – Diamonds in this category will also have high brilliance and scintillation but with greater darkness in the center or around the edges. The pattern of the diamond is also a major consideration. Sometimes, a diamond may be top-notch in all other aspects apart from its pattern that might be imperfect, resulting in a drop from the “excellent” grade to a “very good grade”.

Good Grade – Diamonds falling in this range will generally be darker than those in the higher grades or will have insufficient scintillation and brilliance. The pattern, moreover, will also be a lesser quality. A diamond could also get this grade as a result of its weight ratio; a diamond has an unduly heavy weight ratio when it is heavier than an average gem of the same diameter. In such an instance, it will be downgraded one step.

Fair Grade – A diamond with this grade will generally be one that seriously lacks brilliance or scintillation. It could have dark patches in major areas of the diamond, such as the table area and/or the girdle. Faulty cutting and noticeable imperfections in the symmetry and proportion of the diamond could also be reasons why it has been put in this grade.

Poor Grade – The diamonds that fall into this category are those with markedly faulty features. They will generally have very poor proportions and symmetry as a result of poor cutting with very little brilliance or scintillation. It is in this category that you will find “nail heads” wherein the stone has a black patch right in the center. It will also have “fish eyes”, meaning that the brilliance is totally washed out in the middle. Here again, the weight ratio of the stone is an important consideration.

Apart from features like brilliance, scintillation, weight ratio, and symmetry that have been discussed above, other factors considered by the GIA diamond cut grading process include durability, including thin girdles and inclusions. These inclusions act to weaken the gem and polish, which covers the overall quality of the stone’s surface polish, noting any nicks, scratches, chips etc.

AGS Proportion-Based Cut Grade System

The AGS proportion-based cut grade system is a major challenger to the GIA grading system for dominance as the industry’s standard grading system. Both the AGS and the GIA were funded by the same person, the famous Robert Shipley. But, on account of disagreements over the parameters and methodology by which diamond cuts should be graded, both organizations drifted apart, leading the AGS to establish its own lab and grading system.

As opposed to the GIA system which gives an overall designation based on taking all the diamond’s features into consideration, the AGS’s proportion-based cut grading system considers the color, clarity, and cut of the diamond and assigns each feature of the diamond one of 11 levels ranging from 0 to 10—0 being the best while 10 the worst. A diamond that receives three 0s is one that has been cut perfectly, carrying a flawless polish and perfect proportions and symmetry. Such a diamond must also have the best possible light performance.

Clarity Scale – The clarity scale, as the name implies, measures the clarity of a diamond and the extent to which it contains inclusions. A 0 level on this scale indicates that the diamonds are flawless and include no noticeable inclusions, making the clarity unblemished. Levels 1 and 2 are described as being “very very slightly included” while levels 3 and 4 are “very slightly included”. Diamonds that are given levels 5 and 6 on this scale will have noticeable, albeit still slight, inclusions. Diamonds given levels 7, 8, 9, and 10 will have substantial inclusions simply described in the grading system as “included”.

Color Scale – The scale measures exactly what its name says; the color of the stone. A diamond that is assigned a level of 0 to 1.0 is one that is completely colorless and meets the industry ideal regarding diamond color. Those with 1.5 to 3.0 are described by the grading system as being “near colorless”, while those from 3.5 to 5.0 have faint colorations that are just slightly visible to the naked eye. Diamonds graded 5.0 to 7.0 have “very light” coloration, whereas the coloration present in those with levels 7.5 to 10.0 is still light, albeit more noticeable. Any diamond with coloring beyond 7.5 to 10.0 will be one with the fancy yellow color and is considered less valuable.

Cut Scale – This measures the quality of the diamond’s cut. A diamond with a 0 level will be one that has a flawless cut and perfect symmetry. Such a diamond may even have a pattern of light and dark areas when viewed, possessing high brilliance and scintillation. The polish of the diamond is perfect and it is totally lacking in any nicks, scratches or chips. Diamonds with grades 2 and 3 are “excellent” and “very good”, respectively. Although they have similar characteristics as an ideal cut diamond, they do not have the same grade of perfection and flawlessness. Levels 3 to 4 comprise of diamonds that are described by the grading system as “very good” while those with 5, 6 and 7 are “fair”, which reflects a lower quality of cut. Poorly cut diamonds with obvious flaws, faulty patterns, and symmetry, low brilliance and scintillation occupy the last range from 8 to 10.


We have discussed and compared the various certifications and grading systems that different diamond labs offer.