Grade Expectations: How to Choose a Diamond Lab

At some point in your career, you’re bound to encounter a gem that demands greater investigation than you can do comfortably on your own. You may come across a diamond of high color—possibly even fancy color—or an important diamond with a borderline call on the clarity grade. You’re then faced with the question of which lab to send the gem to. There are many labs in the trade, but common standards are few.

So how do you go about choosing a lab? This article examines some of the trends and controversies surrounding diamond grading and discusses what distinguishes one lab from the next. Below is a list of major diamond labs, the services they provide, and their fees. In a future issue, I’ll explore issues pertaining to colored gemstone grading.

Why use a lab? One reason to send a diamond to a lab is authentication. With the emergence of synthetics that can fool the average jeweler or gemologist, this is more important than ever. Imitations such as cubic zirconia or synthetic moissanite should cause little concern, but even with these, some jewelers may desire the higher comfort level that comes with lab inspection. Distinguishing natural from enhanced stones is also required for fancy-color diamonds. The sophisticated equipment and scientific knowledge used to determine the origin of these diamonds are necessary to justify the high prices of naturally colored diamonds.

A second reason to use a lab, and clearly the most pressing one, is for color and clarity grading. Many jewelers feel that they can compete only by using reports. They know customers are highly informed. Many consumers are even demanding grading reports. A report gives the jeweler a chance against a competitor who is misrepresenting grades. There’s still room for deceit, but an independent report helps level the playing field.

A third and growing need for diamond reports pertains to cut grades. While some labs—such as the Gemological Institute of America’s Gem Trade Laboratory—don’t offer a specific cut grade, others—like the American Gem Society Laboratories—do. There’s been a lot of controversy within our industry over cut grading. Standards for the best cut vary among grading labs that offer this service.

Why use the GIA lab? Many labs offer these services, but the best-known is the GIA Gem Trade Laboratory. It still carries the highest authority in diamond grading, and it’s the lab by which all others are measured. Still, there’s plenty of business for everyone, and other labs grade thousands of diamonds each year.

To demonstrate the preeminence of the GIA lab, I recently did a search of diamonds for sale on the Polygon Trading Network. A search for 1- to 1.05-ct. round diamonds of I color and SI1 clarity turned up 63 diamonds with laboratory grading reports. The top 10 diamonds from the GIA lab had an average selling price of $3,840 per carat. The top 10 from other labs combined had an average selling price of $3,540 per carat. The premium for a GIA report in this category appears to be about 8%.

Now, you could argue that dealers might choose to send better-cut diamonds to GIA, so that it’s the cut and not the lab that accounts for the premium. But a quick assessment of the cuts revealed no significant difference among these top 20 diamonds. I’ve repeated this experiment many times with many different grades, and the results are almost always the same. GIA-graded diamonds sell for at least a few percentage points more on average.

Cut grading: a new frontier. Cut grading is a welcome addition for jewelers looking for a way to make their store stand out. Now, when customers approach armed with color and clarity requests and a price from the competition, the savvy jeweler can use cut as ammunition. “What is the cut grade?” the jeweler now asks. This opens a whole new area of discussion. The jeweler can educate the consumer and point out that cut differences can raise or lower prices by 10% to 20% and in some cases as much as 50%.

To compete for business, diamond wholesalers have also jumped on this bandwagon and have begun promoting better cuts. There’s a lot of competition today on the wholesale level. With so many companies cutting and promoting Ideal cuts, premiums are not as high as they once were (although individual trademarked cuts may still be more expensive). The ultimate winner is the consumer. More consumers are shopping for cut today and often finding competitive prices. Cutting standards in general seem to be improving as the emphasis shifts to cut. This is good for the industry as a whole following several years of lower standards.

Just what is the best cut? GIA has developed cut-grading parameters that are taught in its courses but not used in its lab. The cut classes are 1, 2, 3, and 4, with class 1 the best and 4 below average. GIA lab technicians do not use cut grades on their reports because such grades are believed to be too subjective. GIA’s study of brilliance, which appeared in the Fall 1998 issue of Gems & Gemology, showed just how difficult it can be to attach grades to specific cutting parameters. Various combinations of cut parameters yielded different weighted light return results, not always as expected with certain cut parameters. Although GIA has considered adding more cut information to its reports, such an addition is not currently planned.

On the other hand, the American Gem Society Laboratories does grade cut. The lab uses a scale from 0 to 10, 0 being the best. A diamond graded as 0 is called an AGS Ideal cut. The parameters that qualify a stone for that distinction are: table, 52.4%-57.5%; crown angle, 33.7°-35.8°; pavilion depth, 42.2%-43.8%; girdle thickness, thin to slightly thick.

The Gem Quality Institute laboratory uses the Tolkowsky model—53% table, 34.5° crown angle, and 43% pavilion depth—as a starting point in grading cut parameters. If a diamond falls within the tolerances GQI has established, an additional statement is placed on the report referring to the tolerances and Tolkowsky. GQI notes on its Web site that since polish and symmetry are not considered, this statement should not be construed as a cut grade or the same as the AGS Ideal cut. Other labs are beginning to offer cut-grading services, seeing an economic advantage in the growing demand for cut information.

The recently developed Brilliance Scope from GemEx in Milwaukee, which measures the light return of a diamond in terms of white light (brilliance) and colored light (dispersion), could revolutionize the way laboratories grade for cut. Numbers do not necessarily translate to how a diamond looks to the consumer.

The lab game. A recurring issue of great concern to jewelers is the accuracy and consistency of lab results. Most are familiar with the “lab game,” whereby a dealer will send a diamond to more than one lab hoping to get a more favorable grade. This doesn’t imply that other labs are necessarily more lenient in their grading practices. Whether or not one lab is stricter or more lenient than another is an ongoing debate. Everyone is quick to point to the diamond that supports his or her case.

Remember, however, that diamonds are still graded for the most part by human observation, which is subjective and therefore fallible, especially when it comes to judgments of clarity. Machines are used in many labs to aid in color grading, but because of certain limitations, a person still has the last say. Grading, therefore, can’t be completely scientific, and there will always be differences of opinion.

Within each major lab there are many graders, and their own skills and personal preferences influence the grading process. I’ve seen GIA grades higher than what I would have given. In other instances, I’ve seen stones whose GIA grade was lower than I would give. The same holds for other laboratory reports I’ve analyzed over the years. We often hear rumors about trends. “Did you notice that lab XYZ has eased its standards?” a colleague might say. Or, “Wow, lab ABC has really gotten tough this last year.” Is this really happening? I doubt that the labs consciously alter their standards.

A lot is at stake. Many diamonds are borderline calls, and the difference between two grades can mean hundreds or even thousands of dollars on a large diamond. So if grading standards have indeed changed, as some insist, the impact on the industry is staggering.

Another game that has been played is sending diamonds to two different facilities of the same lab. GIA has two laboratories, in New York and Carlsbad, Calif. (formerly Los Angeles). Dealers unhappy with a grade from one GIA lab would send the diamond to the other, hoping for a higher grade. Of course, they paid two grading fees and there was no guarantee of getting a higher grade.

Today, this is more difficult to do because the labs are connected by computers. When a diamond is submitted, the system can check to see if the diamond has already been at the sister lab. While it can’t catch every diamond, the larger, more unique diamonds are easy to spot. According to Gary Roskin, a former GIA employee and now JCK’s gemstone editor, the risk of being caught increases with a diamond’s size. In his book Photo Masters for Diamond Grading, he writes, “Dealers may send diamonds under five carats through the laboratory many times with less risk of them being found in the computer records. For diamonds over five carats it is more difficult to play the game.”

Choosing a lab. In the gem industry, choosing a laboratory can be confusing. When it comes to labs, the alphabet soup of acronyms is at full simmer: GIA’s GTL, AGL, SSEF, EGL, HRD, GQI, IGI, etc. There are hundreds of labs, and at least a dozen in the United States and throughout the world that are considered “major” ones.

For many jewelers, the key determinants in choosing a lab are the fees and turnaround time. Some jewelers may make their decision based on the lab’s location. But this is generally a consideration only if the lab is based in their own city. Since the item will most likely be mailed to the lab, location really shouldn’t matter. Also consider the reputation and capabilities of the lab. The GIA laboratory is still regarded as the best, although it may not offer the services you require. In cases of dispute, however, it’s often thought of as the lab of the highest authority.

Richard B. Drucker is president of Gemworld International and publisher of The Guide, a pricing periodical he began in 1982. An international gemstone consultant, he has published numerous books on the jewelry industry.

Diamond Grading Laboratories

Here’s a selective list of major diamond laboratories, a brief description of their gemological services, and their basic fees. Since we can’t print full price lists here, a sampling of prices is given. Also remember that many labs offer discounts for members. Only basic trade prices are shown here. For more information on their services, turnaround time, etc., contact the labs.

AGS, American Gem Society Laboratories

8881 W. Sahara Ave., Las Vegas, NV 89117

Phone (702) 233-6120, fax (702) 233-6125,

Peter Yantzer, director

The lab is owned 51% by AGS and 49% by private investors. Services include diamond-grading reports for color, cut, and clarity. AGS, a pioneer in cut-grading reports, has its own grading scale for cut, applied when requested. The “AGS 0” is AGS’s version of the “Ideal” cut. Diamond consultations are $30 and up. Grading reports: .50 ct. for $63, 1 ct. for $97, 2 cts. for $147.

EGL USA, European Gemological Laboratory

30 W. 47th St., New York, NY 10036

Phone (212) 730-7380, fax (212) 730-7453

Mark Gershburg, manager

Services include diamond grading for color and clarity, mini-consultations, and fancy-color diamond-origin reports. EGL also offers appraisal services. Diamond consultations are $30 and up. Grading reports: .50 ct. for $50, 1 ct. for $55, 2 cts. for $110.

GIA, Gemological Institute of America Gem Trade Labs

(1) 580 Fifth Ave., New York, NY 10036

Phone (212) 221-5858, fax (212) 575-3095,

Tom Yonelunas, CEO

(2) Robert Mouawad Campus, 5355 Armada Dr., Suite 200, Carlsbad, CA 92008

Phone (800) 421-7250, fax (619) 603-1814

Sally Ehmke, director

Services include diamond color and clarity grading reports and fancy-color diamond-origin reports. Laser inscription service is also available. The latest offering is the Diamond Dossier for diamonds between .23 and .99 ct. Prices range from $48 to $70 and include inscription of the report number. Grading reports: .50 ct. for $77, 1 ct. for $118, 2 cts. for $179.

GQI, Gem Quality Institute

(1) 550 S. Hill St., Suite 1595, Los Angeles, CA 90013

Phone (800) 235-3287, fax (213) 622-3138

(2) 5 S. Wabash Ave., Suite 1905, Chicago, IL 60603

Phone (312) 920-1541, fax (312) 920-1547,

Tom Tashey, principal

GQI offers diamond color and clarity reports and was the first to offer “mini-certs” to the trade. Tolkowsky cuts are stated if within certain proportion parameters. The lab now offers a branding statement on the report when requested by clients with brand-name trademarks. Diamond mini-reports are $15 and up. Grading reports: .50 ct. for $75, 1 ct. for $85, 2 cts. for $170.

HRD, Hoge Raad voor Diamant

Hoveniersstraat 22, 2018 Antwerp, Belgium

Phone 32-3-222-05-11, fax 32-3-222-07-24,

Mark Van Bockstael, director

Services include diamond color and clarity grading reports and fancy-color diamond-origin certificates. Grading reports: .50 ct. for $50, 1 ct. for $70, 2 cts. for $120.

IGI, International Gemmological Institute

575 Fifth Ave., New York, NY 10017

Phone (212) 753-7100, fax (212) 753-7759,

Jerry Ehrenwald, owner

Services include diamond grading color and clarity reports and appraisals. Laser inscription service is also offered. Diamond consultations are $25 and up. Grading reports: .50 ct. for $50, 1 ct. for $65, 2 cts. for $110.

SSEF, Swiss Gemmological Institute

Falknerstrasse 9, CH – 4001 Basel, Switzerland

Phone 41 61 262 0640, fax 41 61 262 0641,

Dr. Henry A. Hanni, director, also an associate professor of gemmology at Basel University

Because of the international clientele, reports are offered in English, German, and French. The lab produces color and clarity grading reports and fancy-color diamond-origin certificates. Grading reports: .50 ct for SF$270, 1 ct. for SF$350, 2 cts. for SF$510 (roughly $180, $233, and $340 in U.S. currency).

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