GIA vs AGS | The Diamond Cut vs Clarity Difference

GIA vs AGS | The Diamond Cut vs Clarity Difference

GIA vs AGS | The Diamond Cut vs Clarity Difference

Posted by Sharif Khan on 1st May 2019



Diamond certification or grading is one of the seven factors that determine the price of a diamond. While the other six factors are explained below, let’s first discuss the two powerhouses when it comes to grading diamonds, AGS (or AGSL) and GIA.

In our opinion, GIA has an edge over AGS because it has shown the kind of consistency that no lab in the world has shown, and over an extended period of time. However, there are still specific areas where AGS has a slight edge over GIA.

Let’s first find out who they are and why they do what they do. 

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. 

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 four 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. Like we said, it is a powerhouse.

GIA mainly offers two types grading reports, the diamond dossiers and full grading reports. Dossiers are small reports without the full clarity plot on them, and they are often intended 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 make a 99% accurate assessment of a stone based on its report without physically seeing the diamond.

Because GIA is mainly an educational institute, and a non-profit one, they offer the kind of credibility that is hard to match. Even GIA graduate gemologists are well-respected and their educational certificates are highly in demand.

It can be argued that GIA’s 4Cs and continued research and publication has truly transformed the diamond industry.

The one area where GIA is still making more exploration and still do not feel confident to offer conclusive results is the issue of the cut. 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 grade in a wide range as opposed to AGS which uses a specific proportion-based system. GIA’s argument is that the proportions can be modelled differently in order to achieve optimal fire, brilliance and scintillation, and that one rigid proportions-based system is not the right approach to determine the cut grade of a diamond. Please read our detailed article on GIA diamond proportions for reference.

James Allen

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 membership basis. As part of its commitment to learning and education, AGS founded the American Gem Society Laboratories (AGSL) in 1996. AGS also has an advanced instruments division founded in 2004.

As you can see, AGS’s labs are relatively young as they were founded in 1996 compared to GIA that was founded in 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. Depending on your budget, 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 as slightly superior to GIA since it uses precise measurements of cut, table, girdle, crown angle, pavilion angle, cult etc. to determine the cut of a polished diamond. However, one can’t also entirely dismiss GIA’s position of modeling cut with different proportions as it was based on solid research.

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 shape stones other than to round diamonds.

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

GIA Certified Diamonds

Conclusion on GIA vs AGS…

While both are powerhouses and safe labs, it is fair to assert that GIA has an edge over AGS simply because of its reputation and grading consistency. It is true that AGS’s proportions-based cut system is helpful in getting a better cut stone. 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 ideal or super ideal range. What can’t be remedied is AGS’s inconsistency in grading clarity properly. Imagine if you buy a diamond that is graded by AGS as SI2, but it in fact is I1 in GIA’s scale, what would you do to remedy it? Nothing, but to accept the fact that you paid extra for a lower clarity grade diamond!

Let’s discuss the 6 other factors that affect the price of a diamond…

So 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 round or oval are larger in overall diameter than say a square princess cut in each given 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. Because of this reason, it usually takes a larger rough unpolished diamond to get 1 carat round polished diamond than it would for a 1ct. princess cut diamond. If you are going to use a bigger rough to cut a 1ct round diamond, you might as well charge for it because you will waste more carat weight cutting a rough into a round than you would in other shapes. Make sense?

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 the scarcity element of the stone, the rare the stone the higher the price.

Because larger diamonds are scarcer than smaller stones, 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.

What about diamond cut?

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 diamond cut while shopping for a diamond.

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 and 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.

The importance of diamond clarity…

At the very least, most people want their diamonds to be eye clean. Diamond clarity assesses pureness/cleanness of a diamond from natural inclusions. As diamonds are formed under immense pressure beneath the earth surface, most diamonds end up having inclusions in the form of crystals, clouds, feathers, and pinpoints etc. 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.

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 it actually is. The price of a diamond is discounted to a degree depending on the level of fluorescence that 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 options. Please follow our guide on diamond fluorescence for more details.