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 will be mainly dependent on how the diamond is graded in the grading report and/or "certificate”.

The Gemological Institute of America's (GIA), HRD Lab's, American Gem Society's (AGS), and Gem Certification and Assurance Lab's (GCAL) reports command the highest premium in the industry. However, among all the other grading labs, there is a 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, GIA is still considered the standard-bearer in the industry when it comes to educating customers about diamonds. They are the most consistent at grading diamonds as well. 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 of each lab to save you time. 

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 would give you various reasons to justify that a grading report is not necessary. So, they can convince you to buy a stone that is not graded by a reputable lab. If they sell you one-grade off a diamond, they would make a lot more money. Therefore, 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 would send their stones to GIA for grading because they are confident in the quality of their diamonds. The only reason they would send them to other labs for grading. Is because they think these labs will give them better grading results than GIA.

We know that GIA is extremely strict and professional in grading diamonds. The only factor you have to look for is the cut in GIA reports. In round cuts, they offer a cut grade, but they do not in other shapes. This was remedied by following our guidelines on ideal proportions for each shape. As long as you follow these proportions, you will not go wrong with a GIA graded diamond. It may be helpful to verify a GIA report here.

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

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

GCAL is a great lab but has a small market share. They are on par with GIA to a large degree. So, if you see a  GCAL graded diamond, don’t hesitate to purchase it. Ideally, the 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.

Sometimes, you may get conflicting opinions because gemologists will tailor their opinions to the lab that graded their diamonds so they can make sales. These opinions are biased so you should be leery of such opinions while you are 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, everyone works with the same set of dealers and they 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 we also 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 that will at times have one or two grade inconsistencies. The Professional Gem Science Laboratory (PGS) is also a dependable lab but does not have a significant market share. Moreover, GCAL is a very reputable lab, but it does have 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, GIA also trains gemologists and offers in-depth education and research support for the diamond industry. Presently, GIA’s diamond grading reports are the top-rated diamond “certification” and verification documents in the industry.

GIA offers two types of diamond grading reports-full reports and diamond dossiers for small diamonds. The dossiers are less expensive than the full reports and they don’t include the full plot of the diamond which shows the exact location of inclusions in a diamond. Because the location inclusions are not determined in dossier reports, GIA will require a mandatory laser inscription of the diamond. This is not the case with full reports. Diamond dealers can buy the laser inscription as an added service for $30, but it is not a requirement.


There are discussions on how GIA determines excellent cuts in diamonds. The issues are their criteria may be too broad when they assign excellent cut grades to diamonds (which is the highest in GIA’s scale). It has been suggested that because AGS uses a proportion-based system for assigning the IDEAL cut grades in their reports that its grading is superior to GIA's grading. 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 (American Gem Society Laboratories – AGSL) were founded in 1996. They also have an advanced instruments division founded in 2004. AGSL is the division that grades diamonds and they developed their own standards for grading diamonds. AGSL is a close competitor to GIA having a strong reputation in the diamond industry.


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

HRD Certification

HRD Antwerp is mainly owned by Antwerp World Diamond Center. AWDC was founded in 1973 and represents the Belgian diamond industry. As you might know, Antwerp is one of the main centers for diamond trading and supply. HRD Lab’s standards are similar to those used by GIA. They also follow grading rules set by the International Diamond Council. HRD Labs 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. Keep this in mind, as you consider buying HRD graded diamonds. HRD 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. IGI has several branches worldwide and they are one of the largest labs in the world. It also has a gemology school. Because IGI is so large their labs in different countries seem to use slightly different criteria while grading diamonds, this causes overall grading inconsistencies. However, they are improving their overall performance. We would grade IGI as slightly less strict than GIA or AGS. You can expect one grade inconsistency while buying IGI diamonds. However, no two diamonds are identical, so generalizing anything when it comes to buying diamonds is not a good idea – each case will be different so treat each case as different.


You can expect one grading inconsistency in overall grading 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. GSI is a favorite choice of large stores because they grade diamonds much faster than GIA or AGS. GSI is close to IGI in grading diamonds and they usually grade diamonds one grade lower than GIA or AGS. Again, as it was stated earlier each diamond will have its own characteristics. So, these insights are good for general information purposes so it is important to consider every diamond on an individual basis. However, if you aren’t well-informed or if you don't have the time to learn about diamonds, then go for either GIA or 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, so you will be trading 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 their credibility. They are reorganizing the organization and for the time being, you should not solely rely on EGL reports. 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 1950 to early 2000. Even in these, you can expect up to two grade inconsistencies in 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 doesn’t eliminate it. Grading labs have been known to give different grades to diamonds that are sent to them for the second time, and 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. All they will say is that they grade diamonds based on their best judgments.

Consistency of result:

Part of the reason for AGS and 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 minor differing grades. These types of differences are generally accepted in the industry, but when a single lab’s own evaluation disagrees, it is considered a sign of shoddy work.

Certificate Standards:

Another major consideration for diamond certification is the certification standards that the various labs operate by. In illustrating this point one could consider GIA and IGI side by side: GIA is a non-profit organization while IGI is a commercial institution. As is expected, GIA is known to be more objective than IGI when grading diamonds. Simply because the latter is bound by their profit motive to be more customer-oriented (the customers, in this case being diamond merchants.) This disparity in results is an open secret in the industry. Sometimes, commercial labs would give diamonds an average of one point higher grading than those given by GIA and AGS just to make its clients happy. Here is what this means for you as a buyer. You may find two diamonds with similar grades from IGI and GIA, with the one from IGI having a lower price tag than the one from GIA. It seems like a bargain to purchase the diamond at a lower price; but you paid the same  price as the diamond graded by GIA, who gave it a lower grading, so it will be sold for a lower price.

Basically, from a buyer’s perspective, diamond certification is critical when buying a diamond. The diamond grading or certification comes from a wide variety of labs. The diamonds are graded with varying reliability, but to get the best deal you should purchase a diamond that has either been certified by GIA or 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 the other aspects, but have a pattern that is imperfect, resulting in a drop from the “excellent” grade to a “very good grade”.

Good Grade – Here, the diamonds will generally be darker than those in the higher grades, or having insufficient scintillation and brilliance. The pattern will also be of lesser quality. A diamond could also get this grade as a result of its weight ratio. A diamond has an unduly heavyweight 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 the girdle. Faulty cutting and noticeable imperfections in the symmetry and proportion of the diamond could also be reasons it has 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, as well as having little brilliance or scintillation. It is in this category that you will find “nail heads”, where the stone has a black patch right in the center. It will also have “fish eyes” which means the brilliance is washed out in the middle. Here again, the weight ratio of the stone is an important consideration.

Apart from the features like brilliance; scintillation; weight ratio and symmetry which have been discussed above. The other factors considered by the GIA diamond cut grading process will include durability, including thin girdles as well as 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. Due to disagreements over the parameters and methodology by which diamond cuts should be graded, both organizations drifted apart, leading AGS to establish its own lab and grading system.

As opposed to the GIA system which gives an overall designation that is based on considering all the diamond’s features. 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. Of Course,0 is the best, and 10 is the worst. A diamond that receives three 0s is one that has been cut perfectly, it has a flawless polish, and it has perfect proportions and symmetry. It also has the best possible light performance.

Clarity Scale – The clarity scale, as the name implies, measures the clarity of the diamond and to the extent it contains inclusions. A 0 level on this scale indicates the diamonds are flawless and they include no noticeable inclusions in which makes the clarity flawless. 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 which are 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”, from 3.5 to 50 have faint colorations that are just slightly visible to the naked eye. Diamonds graded 5.0 to 7.0 have “very light” coloration while the coloration present in those with levels 7.5 to 10.0 is still light, but 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. It also has perfect symmetry. The diamond even has a pattern of light and dark areas when viewed. It also has high brilliance and scintillation. The polish of the diamond is perfect and it is lacking in any nicks, scratches, or chips. Diamonds with grades 2 and 3 are “excellent” and “very good” respectively. They have similar characteristics as an ideal cut diamond, but they do not have the same grade of perfection and flawlessness. Levels 3 to 4 comprise 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 and low brilliance, scintillation as well as faulty patterns and symmetry occupy the last range, from 8 to 10.


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