The retail price of a diamond largely depends on how the diamond is graded in a grading report and/or "certificate.”
Grading reports by the American Gem Society (AGS), Gemological Institute of America (GIA), and Gem Certification and Assurance Lab (GCAL) command the highest premium in the diamond industry. However, among the other labs, there are often discrepancies in how they grade diamonds and assess the 4Cs.
Check James Allen's 3D 360-degree image technology for assessing the cut of AGS and GIA-graded diamonds before buying them.
Please carefully review our ranking below for the best diamond certification labs in the world. We have also provided additional insights on each lab in the subsequent sections.
Overall, AGS and GIA are the standard-bearers in the diamond industry when it comes to grading diamonds. Check our additional insights below about AGS vs. GIA grading systems and where one may have an edge over the other. Furthermore, check this article on IGI vs. GIA for your review as well.
Check examples of these grading reports at Blue Nile or Brilliant Earth as they have an extensive collection of both natural and lab diamonds for comparison purposes. Whiteflash is an exceptional choice for AGS ideal cut diamonds.
Key Takeaways on Diamond Certification:
A diamond certification or grading is extremely important. Do not buy a diamond that is not accompanied by a grading report from a reputable lab. Local jewelers will try to justify why a grading report is unnecessary and convince you to buy an ungraded diamond. By doing so, even if they succeed in selling you a diamond that is one grade lower, their profit will be substantially higher.
Reputable diamond dealers will often send their stones to AGS or GIA for grading to stay consistent and because they appreciate transparency. Both AGS and GIA are often strict and professional in how they grade diamonds.
AGS is a top grading lab and is improving how they grade clarity more accurately in lower grades, especially in SI2 diamonds. It is the best in grading the cut grade of a diamond as AGS uses a proportion-based system.
Buyers would need more preparedness with assessing the cut grade in a GIA grading report. GIA offers a cut grade in round diamonds only. Even in round diamonds, our guidelines on ideal proportions for each shape are critical in distinguishing between a super ideal cut and an average excellent cut GIA-graded diamond.
IGI is a decent lab but not as good as AGS or GIA. If you are buying a lower color grade diamond (I-J-K), IGI is perfectly fine for the purpose. However, if you want to buy a premium-grade diamond, always stick with AGS or GIA.
GCAL is a reputable lab but has a small market share. They are on par with AGS and GIA. Therefore, if you see a GCAL graded diamond, do not hesitate to purchase it. Often a GCAL diamond also comes with a GIA report.
Getting conflicting opinions on diamond labs is common because dealers will often tailor their opinions in favor of a lab that might have graded their diamonds. To make a better decision, follow our in-depth diamond guide for each shape.
An Illustration of GIA Excellent Cut vs. AGS Ideal Cut Diamond: (Click on each image to watch a 3D Video of the Diamond). If you are shopping for high-quality AGS-graded ideal cut diamonds, check out Whiteflash. They have the largest selection of in-house AGS-graded diamonds.
A Review of Each Diamond Certification Lab:
In short, we highly recommend GIA as the top lab and consider AGS, HRD, and GCAL as reliable labs as well. The International Gemological Institute (IGI) is also improving its process for grading diamonds. Unfortunately, The European Gemological Laboratory (EGL) has lost much of its credibility and market share. The Gemological Science International (GSI) is a satisfactory lab and at times might have one or two grade inconsistencies. The Professional Gem Science Laboratory (PGS) is also a dependable lab but does not enjoy much popularity.
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. AGSL is the division that grades diamonds and has developed its standards for doing so. It is a close competitor to the GIA and has a strong reputation in the diamond industry.
When grading a diamond's clarity, AGS needs to more grading SI1/SI2 diamonds. We have noticed diamonds in the SI2 range graded by AGS that were more like I1. So, when it comes to clarity grading in the SI2 range, be wary of AGS's inconsistencies.
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 top-rated diamond “certifications” 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 do not include the full plot of a diamond that shows the exact location of inclusions. Because the locations of inclusions are not determined in dossier reports, GIA will require a mandatory laser inscription of the diamond. This, however, is not the case with full reports. Diamond dealers have the option to buy the laser inscription as an added service in full reports for an additional $30.
As GIA has grown, the quality of its graded services seems to have suffered. Recently, we have seen GIA regard its own G color graded diamond as lower H color.
There are discussions on how GIA determines excellent cuts in diamonds. One issue with their grading is their broad criteria when assigning excellent cut grades to diamonds; excellent cut grades are the highest on GIA’s scale. It has been suggested that because AGS uses a proportion-based system for assigning ideal cut grades in their reports, its grading is superior to that of GIA. Please look up diamond proportions and use our chart to buy a well-cut GIA graded diamond.
As you might know, Antwerp is one of the main diamond trading and supply centers. HRD Antwerp is mainly owned by the Antwerp World Diamond Center, founded in 1973, representing the Belgian diamond industry. 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 grading diamond color and clarity. Please consider this as you buy HRD graded diamonds.
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, is one of the largest labs in the world, and also has a gemology school. Because IGI is extremely large, spanning across the world, their labs in different countries use slightly different criteria while grading diamonds. We would rate IGI as slightly less accurate than GIA or AGS. You can expect one-grade inconsistency while buying IGI graded diamonds. However, no two diamonds are identical, so applying a generalized approach 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 regarding IGI's grading in all 4Cs.
Gemological Science International mainly grades diamonds for large chain stores in mass numbers. Recently, they have expanded their operations to many countries worldwide. GSI is a favorite choice of large stores because they grade diamonds much faster than GIA or AGS. Its accuracy is close to IGI in grading diamonds and usually grades diamonds one grade lower than GIA or AGS. Again, as it has already been stated, diamonds must be considered individually because each diamond has its own characteristics.
If you are not well-informed or if you do not have the time to do the necessary research, go for either GIA or AGS.
It is wise to be cautious when evaluating GSI's diamonds. Expect a grade inconsistency. 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 most likely be making a trade-off when buying GSI graded diamonds.
The European Gemological Laboratory used to have significant shares in the diamond grading business; however, it has lost much of its credibility. EGL is reorganizing the organization, and, at least for the time being, you should not rely solely on their reports. As a result of their bad 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 1950s to the early 2000s. Even among these, you should expect up to two grade inconsistencies in the overall grading.
How are Diamonds Certified?
In order to make an informed decision on the various diamond grading reports/certifications, it is critical to understand how diamonds are graded in the first place.
The major grading 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 diamonds. The final grades are 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 does not entirely eliminate it.
Some labs have inconsistencies when grading diamonds for the second time. This inconsistency is more noticeable when a more consistent/stricter lab reevaluates a diamond graded by an inferior lab.
Diamonds are not certified; no lab would say they are "certifying" diamonds. It can cause them trouble legally speaking, so all they confirm is that they have graded a diamond based on their best opinion/assessment as represented in the grading report.
Consistency of result:
Part of the reason behind AGS's and GIA's dominance is their consistency, in that they can consistently grade diamonds accurately. If you were to send a diamond to AGS or GIA for evaluation, you would probably receive identical grading results without major discrepancies.
A small difference is an acceptable norm within the industry though.
The organizational structure of each lab matters:
AGS is a membership organization and GIA is a non-profit organization. As such, AGS and GIA are known to be more objective than other labs when grading diamonds.
Other labs are influenced by profit motives and are more customer-oriented, the customer being diamond merchants. As a result, the industry's disparity in grading results is an open secret. Sometimes, commercial labs would give diamonds one point higher grading on average than AGS or GIA to make their clients happy.
If you find a diamond with similar grades from a different lab with a lower price than one being graded by AGS or GIA, do not be misled by its bargain price as the stone might be of lower quality and hence the price difference.
Principally, from a buyer’s perspective, diamond certification is critical when buying a diamond. While there are many labs out there, your best bet is to buy a diamond that is graded by AGS or GIA.
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, GIA’s cut grading system introduced to serve as the standard to judge all the gemstones and diamonds specifically. Although the 4Cs of diamond grading was already well known and several other grading systems were in use, it became necessary to have a uniform grading system to promote consistency across the industry. Today, GIA's 4Cs grading system is the most widely used and accepted grading standard for grading diamonds.
The key features of a diamond the system considers when assigning a grade are: color, clarity, and make, comprising the cut, polish, and finish. Five grades can be assigned to a diamond after GIA evaluation:
Excellent Grade – Diamonds with this grade 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 also have high brilliance and scintillation but 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 are generally darker than those in the higher grades or have insufficient scintillation and brilliance. The pattern, moreover, is also of lesser quality. A diamond can also get this grade due to its weight ratio; a diamond has an unduly high weight ratio. 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 is generally the one that seriously lacks brilliance or scintillation. It can 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 can also be reasons why it has been put in this grade.
Poor Grade – The diamonds that fall into this category have markedly faulty features. They generally have very poor proportions and symmetry due to poor cutting with very little brilliance or scintillation. In this category, you will find “nail heads,” wherein the stone has a black patch right in the center. It also has “fish eyes,” meaning that the brilliance is 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 discussed above, other factors considered by the GIA diamond cut grading process include durability, including thin girdles and inclusions. These inclusions 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 AGS and 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 AGS to establish its own lab and grading system.
As opposed to the GIA system, which gives an overall designation based on considering all the diamond’s features, AGS’s proportion-based cut grading system considers the diamond's color, clarity, and cut. It also assigns each feature of the diamond one of 11 levels ranging from 0 to 10—0 being the best while 10 is the worst. A diamond that receives three 0s 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.” On this scale, diamonds given levels 5 and 6 have noticeable, albeit still slight, inclusions. Diamonds given levels 7, 8, 9, and 10 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 assigned a level of 0 to 1.0 is completely colorless and meets the industry ideal regarding diamond color. The grading system describes those with 1.5 to 3.0 as “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 levels 7.5 to 10.0 is still light, albeit more noticeable. Any diamond coloring beyond 7.5 to 10.0 has a 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 has a flawless cut and perfect symmetry. When viewed, such a diamond may even have a pattern of light and dark areas, possessing 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. 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 diamonds described by the grading system as “very good,” while those with 5, 6, and 7 are “fair,” which reflects a lower cut quality. Poorly cut diamonds with obvious flaws, faulty patterns and symmetry, low brilliance, and scintillation occupy the last range from 8 to 10.
In this article, we offered a comprehensive insight into diamond certification and grading systems available worldwide. Herein, we also elaborated on why certain jewelers/dealers will try to convince you that grading a diamond is unnecessary and that you will be better off without it. We hope this article will enable you to make a better, more informed decision.
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