GIA vs AGS | What is the Difference?

Both GIA and AGS are renowned and dependable diamond grading laboratories. GIA displays higher consistency and a more rigorous approach when grading the clarity of SI1/SI2 diamonds, whereas AGS actively enhances its grading methodologies for lower clarity grades.

Comparatively, AGS's proportion-based methodology for cut grading is superior to GIA's process. AGS's scientifically-informed approach, considering light performance and proportions, offers a more accurate assessment of cut quality. Familiarity with GIA's grading reports and insights from our diamond proportions guide can aid in interpreting and optimizing GIA-graded diamonds.

GIA's cut grade encompasses a range from Excellent to Poor. Their color scale spans from D (colorless) to Z (light yellow or brown), while the clarity scale ranges from Flawless (FL) to Included 3 (I3). Conversely, AGS employs a 0–10 scale for cut, color, and clarity assessment, where 0 signifies ideal and 10 indicates poor.

A diamond's certification or grading constitutes one of the seven factors influencing its price. While the remaining six factors are elaborated below, this article primarily delves into the key distinctions between AGS (or AGSL) and GIA, shedding light on their respective contributions to the diamond grading landscape.

The Gemological Institute of America (GIA), established in 1931 as a non-profit institute, serves as a safeguard for gemstone buyers and sellers through comprehensive research and diamond grading. It pioneered the internationally recognized 4Cs grading system (Cut, Clarity, Carat, and Color) in 1953. GIA is headquartered in California and operates across 13 countries, boasting 11 campuses, nine laboratories, and four research centers.

GIA's primary grading report options encompass diamond dossiers, brief reports often for small diamonds lacking a complete clarity plot, and complete grading reports, offering comprehensive information. The latter is often sufficient for professional dealers to evaluate a diamond's quality based on the report without physical inspection.

Due to its nonprofit educational nature, GIA is widely regarded as a reliable lab, with its graduate gemologists commanding respect within the industry. The institution's academic certificates often serve as benchmarks for professionalizing and accrediting expertise as graduate gemologists. Additionally, GIA's formulation of the 4Cs and its ongoing research and publications contribute positively to the diamond industry's advancement.

GIA's exploration of the cut grade remains ongoing, particularly for fancy cut stones like princess or cushion cut diamonds. While it assigns cut grades for round diamonds, it is refining proportions and criteria before extending this to other shapes.

GIA offers a broad range of excellent cut grades for round diamonds, contrasting AGS's specific proportion-based system. GIA contends that proportions can vary for optimal fire, brilliance, and scintillation. It asserts that a rigid proportion-based system isn't the only approach to determine a diamond's cut grade.

As GIA has expanded, its grading consistency has shown some fluctuations recently. An illustrative case involves submitting a large G VVS2 GIA-graded diamond for reevaluation after recutting, where GIA assessed it as a lower H grade, departing from their original grading report.

In summary, GIA's enduring influence is evident through its pioneering initiatives, educational contributions, and ongoing pursuit of precision in diamond grading practices.

The American Gem Society (AGS) was established in 1934, functioning as a trade association uniting jewelers, traders, appraisers, and suppliers. Operating predominantly through membership, AGS embodies a commitment to learning and education, exemplified by the inception of the American Gem Society Laboratories (AGSL) in 1996. In 2004, AGS introduced an advanced instruments division, contributing to its multifaceted pursuits.

In contrast to GIA, whose diamond grading labs have been operational since 1931, AGS's diamond grading facilities are relatively recent developments.

Although AGS adheres to the familiar 4Cs model, it has refined its diamond grading criteria and offers a diverse range of grading reports, with the light platinum grading report earning accolades as one of the finest.

AGS's proportions-based cut grading system is regarded as superior to GIA's, as it employs precise measurements of various facets including cut, table, girdle, crown angle, pavilion angle, and culet to determine a polished diamond's cut quality. However, it is prudent to acknowledge GIA's research-based stance that proportions can be approached through different models.

Furthermore, it's worth noting that AGS extends its cut grade assessments to fancy cut stones like emerald-cut diamonds, a distinction not present in GIA's grading reports for fancy-shaped stones.

In the realm of clarity grading, AGS diamonds may encounter challenges in lower grade categories, particularly within the SI1 and SI2 ranges. Instances have been observed where diamonds graded as SI2 by AGS might receive an I1 (included 1) grade from GIA, showcasing a divergence in assessment.

Please keep in mind that while AGS has introduced novel and commendable approaches, both AGS and GIA contribute valuable perspectives to the diamond grading landscape.

Although both AGS and GIA are reputable diamond grading laboratories, it can be argued that AGS holds a potential advantage over GIA, primarily attributed to its enhanced and consistently applied grading system. Notably, AGS's proportions-based cut evaluation system is more advanced and refined, facilitating an easier and more informed diamond selection process for buyers, eliminating the need for additional research. Nonetheless, this concern can be addressed by familiarizing oneself with the ideal proportions for achieving maximum brilliance and fire in a diamond. To assist in this endeavor, please consult our comprehensive ideal proportions chart and consider purchasing a GIA-graded diamond that aligns with our recommended ideal or super-ideal proportions range.

The primary factors that influence the price of a diamond and how they are graded in GIA or AGS reports include shape, carat weight, cut, color, clarity, and fluorescence.

How does the shape of a diamond impact its price?

In brief, diamond shapes like round or oval cuts have larger overall diameters compared to square princess cuts within each carat weight range. For instance, a well-cut 1-carat round diamond usually measures 6.4-6.5mm in diameter, while a square princess cut of the same carat weight falls within the 5.3-5.5mm range. Consequently, crafting a 1-carat round polished diamond requires a larger rough unpolished diamond than a 1-carat princess cut diamond. As a result, obtaining the former entails higher costs due to the need for a larger rough diamond.

AGS and GIA reports concur on diamond shape evaluation.

How does carat weight influence diamond pricing?

This is a straightforward concept: the larger the diamond, the higher its price. However, there's a caveat. The price of natural diamonds is determined by their scarcity, so rarer stones command higher prices.

Given the rarity of larger diamonds, their prices experience a significant uptick as carat weight increases. In other words, the cost of a 1-carat diamond isn't merely double that of a 0.5-carat diamond (assuming all other factors remain constant); it's around 3 to 4 times higher. The same principle applies to diamonds weighing 2, 3, or 4 carats. Larger gem-quality diamonds are scarce, resulting in substantial price hikes as carat weight escalates.

AGS and GIA reports align when assessing diamond carat weight.

What about diamond cut?

The cut is the sole "C" determined by human hands rather than nature. The other three Cs occur naturally within a diamond.

Diamond cut ranks among the most vital considerations during diamond shopping. Poorly cut diamonds, whether excessively deep or shallow, should be avoided. Follow our diamond cut guidelines when making a purchase.

As previously explained, AGS holds an advantage over GIA due to its proportion-based grading approach.

How does diamond color impact pricing?

Diamond color holds significant importance for white diamonds. The presence of a yellowish tint or hue diminishes a stone's desirability. Diamond color is graded from D to Z, with D-F in the colorless range (considered the best) and G to J falling in the near colorless grades. G is nearly colorless and an optimal choice, while H and I are also excellent options. Consult our diamond color chart for reference. Diamond fluorescence can aid color evaluation; details can be found in the fluorescence section below.

GIA exercises stricter color grading compared to AGS for white diamonds.

The significance of diamond clarity

Most individuals desire diamonds that are at least eye-clean. Diamond clarity gauges a diamond's purity and absence of natural inclusions. Since diamonds form under immense pressure beneath the Earth's surface, they commonly contain inclusions like crystals, clouds, feathers, and pinpoints. Consequently, fewer inclusions enhance a diamond's quality. GIA's clarity scale ranges from Flawless to Included 3 (I3). Flawless to VVS/VS1 grades denote investment-grade diamonds, while VS2-SI1 grades are excellent for maximizing size without compromising clarity. SI2 can be a budget-friendly choice and may still be eye-clean in some cases. I1 to I3 are generally not considered eye-clean. Consult our diamond clarity scale for reference.

GIA employs a stricter approach to clarity grading compared to AGS.

Leveraging diamond fluorescence to your advantage

Fluorescence typically has a negative impact on a diamond's value, but it can be turned to your benefit. Generally, it's advisable to avoid fluorescence in D-G color diamonds (faint fluorescence is acceptable). However, fluorescence can be advantageous in H and lower color grades because blue complements yellow, making a yellowish diamond appear whiter than its true color. The price of a diamond is discounted to a certain degree based on its fluorescence under ultraviolet light. Fluorescence is categorized as none, faint blue, medium blue, strong blue, and very strong blue. Occasionally, fluorescence might manifest in other colors like yellow or green, but it's best to steer clear of them. Consult our diamond fluorescence guide for further insights.

AGS and GIA are in agreement regarding diamond fluorescence, and there are no specific concerns to highlight.