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Is GIA better than AGS [it's not that simple)

Is GIA better than AGS [it's not that simple)

Is GIA better than AGS [it's not that simple)

Posted by Sharif Khan on 12th Nov 2021

GIA vs AGS

AGS vs GIA

Since GIA and AGS are two of the best diamond grading labs in the world, is one better than the other?

In our opinion, overall, GIA has an edge over AGS because it has been a very consistent lab over an extended period of time in how they have graded diamonds. There has been almost no controversy ever over GIA assigning inaccurate grades to a diamond. However, at the same time, there are some specific areas where AGS has a slight advantage over GIA.

Try to compare GIA vs AGS graded diamonds with James Allen's (for GIA) and Whiteflash's (for AGS) 360-degree video technology to get a sense of actual diamonds in 3D and the price difference.

Bottom Line Recommendation:

  • Both GIA and AGS are excellent grading labs and are very reliable.
  • GIA is more consistent and stricter in grading the color and clarity grades of diamonds, especially when it comes to grading SI1/SI2 diamonds.
  • AGS’s proportion-based model for assigning a cut grade to diamonds is more accurate in assessing the cut quality of a diamond. However, it can be remedied in GIA graded diamonds as well if you know how to read their grading reports. Review our diamond proportions guide while reviewing a GIA graded diamond.

A diamond certification or grading is one of the seven factors for determining the price of a diamond. While the other six factors are explained below, this article explores the key differences between AGS (or AGSL) and GIA.

Let’s dig a little deeper into both GIA and AGS and learn more about their history before we offer our concluding thoughts on each lab.

James Allen

The Gemological Institute of America:

The Gemological Institute of America or GIA was established in 1931 as a non-profit institute to protect buyers and sellers of gemstones by comprehensively researching and grading diamonds. GIA developed the 4Cs international grading system (Cut, Clarity, Carat, and Color) in 1953. The Institute is headquartered in California and operates in 13 countries, has 11 campuses, 9 laboratories, and 4 research centers worldwide.

GIA mainly offers two types of grading reports, diamond dossiers, and full grading reports. Dossiers are small reports without a full clarity plot on them --- often issued for small diamonds. On the other hand, the full report is a very comprehensive document and provides sufficient information to professional dealers so that they can accurately assess a stone based on its report without physically seeing the diamond.

Because GIA is mainly a non-profit educational institution, its credibility is highly valid and trusted. Even GIA graduate gemologists are well-respected. Furthermore, GIA’s educational certificates are often a benchmark for how individuals professionalize/accredit their craft as graduate gemologists.

It goes without saying that GIA’s 4Cs and continued research and publication have truly transformed the diamond industry.

The one subject that GIA is still exploring before offering conclusive determinations/results is the issue of the cut grade. In round cut diamonds , GIA offers a cut grade, but in other fancy cut stones, such as princess cut or cushion cut diamonds , GIA does not offer a cut grade yet. In our opinion, GIA is still determining optimal and final proportions/criteria before they assign such cut grades in their reports.

Even in round diamonds, they offer excellent cut grades in a wide range as opposed to AGS which uses a specific proportion-based system. GIA’s argument is that the proportions can be modeled differently in order to achieve optimal fire, brilliance, and scintillation and that one rigid proportions-based system is not the right approach to determining the cut grade of a diamond. Please read our detailed article on 

GIA Certified Diamonds

The American Gem Society – American Gem Society Laboratories:

The American Gem Society (AGS) was established in 1934. It is more of a trade association of jewelers, traders, appraisers, and suppliers, operating primarily on a membership basis. As part of its commitment to learning and education, AGS created the American Gem Society Laboratories (AGSL) in 1996. AGS also has an advanced instruments division founded in 2004.

AGS’s diamond grading labs are relatively young established in 1996 compared to GIA’s operating since 1931 (with the 4Cs being developed in 1953 by GIA).

While AGS uses the same 4Cs model, they have their own grading criteria for grading diamonds. They also offer a variety of grading reports with the light platinum grading report as one of the best.

AGS’s proportions-based cut grading system is considered slightly superior to GIA since it uses precise measurements of cut, table, girdle, crown angle, pavilion angle, and cult, among others, to determine the cut of a polished diamond. However, at the same time, we should not entirely dismiss GIA’s position that proportions can be modeled differently based on its research findings.

It is also helpful to share that AGS assigns a cut grade to fancy cut stones such as emerald cut diamonds , but GIA does not offer such grades in their grading reports to fancy shaped stones.

The clarity grade in AGS diamonds can be an issue in lower grade diamonds such as SI1 and especially in the SI2 range. We have seen SI2 graded diamonds by AGS that GIA would not grade as SI2, but more as I1 (included 1).

Conclusion on GIA vs AGS:

While both GIA and AGS are amazing diamond grading labs, it is fair to suggest that GIA has an edge over AGS simply because of its reputation and grading consistency. At the same time, AGS’s proportions-based cut system is helpful in terms of buying a well-cut diamond without having to do the extra work/research. However, this issue can be easily remedied if you know what the right proportions are for ideal brilliance and fire. Simply follow our ideal proportions chart and buy a GIA graded diamond that fits our suggested ideal or super ideal proportions range. What we cannot remedy is at times AGS’s inconsistency in grading clarity as strictly as GIA.

The other six factors that affect the price of a diamond and how they are graded in GIA and AGS reports:

In addition to diamond grading reports, there are six other factors that affect the price of a diamond. These include diamond shape, diamond carat weight, diamond cut, diamond color, diamond clarity, and diamond fluorescence.

How does shape affect the price of a diamond?

In short, shapes such as a round or an oval cut are bigger in their overall diameter than say a square princess cut in each carat weight range. For example, a well cut 1 carat round diamond is usually 6.4-6.5mm in diameter whereas a square princess cut 1 carat would be in the 5.3-5.5mm range. Therefore, it usually takes a larger rough unpolished diamond to get 1 carat round polished diamond than it would for a 1 carat princess cut diamond. Because a bigger rough diamond is needed to cut a 1 carat round diamond, the cost of obtaining a bigger rough diamond is obviously going to add up to the overall cost of the said 1 carat round diamond.

AGS and GIA reports are the same when it comes to the shape of the diamond. Nothing, in particular, to worry about.

How does carat weight affect the price of a diamond?

This is a no-brainer, the larger the stone, the higher the price. However, there is a catch to it. Since the price of natural diamonds is determined by how scarce the diamond is, the rare the stone the higher the price.

Because larger diamonds are scarcer than smaller ones, the prices of large diamonds jump upwards significantly as the carat weight increases. In other words, do not expect the price of a 1 carat diamond to be twice as much as the price of a 0.5 carat diamond (all other factors being equal), but 3 to 4 times the price of a 0.5 carat diamond. The same applies to 2, 3, or 4 carat diamonds. Larger gem-quality diamonds are very rare and therefore their prices jump significantly as the carat weight increases.

AGS and GIA reports are the same when it comes to the carat of the diamond.

What about the diamond cut?

The cut is the only C which is determined by human beings and not nature. The other 3Cs are naturally formed in a diamond.

The cut of a diamond is one of the most important factors to consider while buying a diamond. Poorly cut diamonds are either too deep or shallow. Make sure you follow our instructions on the diamond cut while shopping for a diamond.

As explained earlier, AGS has an advantage over GIA because of its proportions-based grading model.

How does color affect the diamond?

Diamond color is an important factor in white diamonds. The more the yellowish tint or hue, the less desirable the stone. Diamond color ranges from D to Z, with D-F color range considered as colorless (the best) and G to J considered as near colorless color grades. G is almost colorless --- an ideal choice, and H and I are also very good choices. Follow our diamond color chart for reference. Diamond fluorescence can be a helpful factor to consider while evaluating the color of a diamond. See below why in the fluorescence section.

GIA is stricter compared to AGS when it comes to grading color in white diamonds.

The importance of diamond clarity:

At a minimum, most people want their diamonds to be eye-clean. Diamond clarity assesses the pureness/cleanness of a diamond from natural inclusions. Because diamonds are formed under immense pressure beneath the earth's surface, most diamonds end up having inclusions in the form of crystals, clouds, feathers, and pinpoints, among others. The fewer the inclusions, the better the diamond. GIA clarity scale grade diamonds between Flawless to Included 3 (I3). Flawless to VVS/VS1 are investment-grade diamonds, VS2-SI1 are excellent options for maximizing the size of a diamond without compromising on clarity, and SI2 could still be a budget option and in some cases also eye-clean. I1 to I3 are not considered eye-clean diamonds. Follow our diamond clarity scale for reference.

GIA grades clarity more strictly than AGS.

How to use diamond fluorescence to your advantage:

Fluorescence is generally a negative factor in a diamond and can affect its price. However, you can use it to your advantage. It is a good idea, in general, to avoid fluorescence in D-G color diamonds (faint is okay), but it can be a very helpful factor in H-above color grades because blue is a complementary color to yellow and therefore can make a yellowish diamond look whiter than its actual color. The price of a diamond is discounted to a degree depending on the level of fluorescence that the diamond emits under ultraviolet rays. Fluorescence is graded in the range of none, faint blue, medium blue, strong blue, and very strong blue. In rare cases, fluorescence could also be in other colors such as yellow or green. It is best to avoid such colors. Please follow our guide on diamond fluorescence for more details.

AGS and GIA are on the same page on comes to diamond fluorescence and nothing in particular to flag here.