Diamond Grading Labs: How to compare different labs and terminology

When you’re buying a diamond engagement ring, it will usually come with a diamond grading report issued by a third-party laboratory (i.e. different from the appraisal issued by your jewelry store) identifying the quality of the diamond. 

In some cases, you may not receive a lab report, especially if the center diamond is under 0.75ct or if the ring is made up of multiple smaller diamonds, as lab reports are less commonly issued for smaller stones. Antique and vintage engagement rings are also often cases in which a lab report wouldn’t necessarily be expected, as many times these older pieces pre-date the existence of these practices; depending on the setting, a diamond could be removed from the setting and sent away to be graded, and then reset in its vintage mounting, but that’s not always possible or practical, so a gemologist’s appraisal can take the place of lab reports for vintage jewelry.

Most of the time, however, when you’re choosing your engagement ring you’ll be considering lab-graded diamonds. To the newcomer to the jewelry trade, the alphabet soup of acronyms like GIA, AGS, IGI, GCAL, EGL or HRD can be a little baffling. These are just some of the independent labs that grade diamonds. As buyers become more educated about what these grades (namely the 4Cs) mean, sometimes questions about the labs themselves arise. 

The biggest question is about comparison– is one lab as reputable as another? Or, if I’m considering two stones graded by different labs, is one lab’s grade better than the others? Can I compare apples to apples? 

The answer is a little complicated. GIA, the Gemological Institute of America, is the most popular lab for grading diamonds in the United States. They actually developed many of the scales and standards of inspection that are industry standards today, and they’re respected the world over for their grades. Their solid reputation doesn’t mean that a GIA-graded diamond is any better than any other diamond solely because it was graded by GIA. A lab doesn’t mine, sell, cut, or polish stones– it simply evaluates their quality factors. GIA, however, is a trusted lab, so you can believe that their grades stand for something objective. 

It’s important that a lab have strict standards for grading and good practices of consistency so that consumers know what they’re buying in objective terms. Most labs grade diamond color on the same D to Z scale, a similar clarity scale (FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, [SI3], I1, I2, I3), weighed precisely in carats out to 2 decimal places, and with various terms to describe cut usually ranking cut as excellent/ideal, very good, good, fair, or poor. The terminology used by different labs seems similar enough, but it can be hard to know if one lab’s E color, for example, is the same color as another lab’s E. 

Apples-to-apples

One way to see how different labs compare is to send the same diamonds to multiple labs and see how the results came out. In 2013, the Rapaport Diamond Trading Network (Rapnet) sent 10 stones of differing weights to GIA, got the results, then sent the same stones to IGI, then to HRD, then EGL USA, then EGL Israel, then EGL Hong Kong. At the end, the ten stones had a total of sixty reports. This process took a very long time to complete, as the stones spent months at each facility, and was considerably costly, as each lab may charge hundreds of dollars for a single report. The results proved that you can’t always compare apples to apples. 

To make it easier to compare the results, Rapnet assigned a numerical value for each of the scores based on the 4Cs to come up with the average quality score for each stone at each lab, with the lower numbers representing the stricter grades and the higher numbers representing the inflated grades.

 

As you can see from the results, there was a huge discrepancy between some of the labs. GIA and IGI had nearly identical scoring, indicating that you could probably compare these two labs’ reports apples-to-apples. 

The other labs surveyed in the Rapnet study showed that you can’t compare their grading practices as equals to GIA. The EGL Hong Kong and EGL Israel labs had very inflated scores. What this means for consumers is that you might purchase something that doesn’t look as good as the report would lead you to expect.

For one of the stones in the study, you can see that GIA and IGI determined it was a 1.01ct K SI1. HRD called it a J SI1, which is slightly inflated, but is a slight enough difference to be explained by lighting variances. On the extreme, EGL Israel called it a G VS1. You’d typically pay a lot more for a G VS1 stone than a K SI1. Based on 2020 trade reports, in fact, a 1.01ct G VS1 is actually 110% more expensive than a K SI1. It’s because of this that grade inflation is such a problem. It’s the exact same stone, but you could pay more than double for it depending on which lab did the report. 

In general, based on tests like these, GIA and IGI grades can usually be compared as equally strict when comparing prices. You’ll know when you’re comparing the price of two diamonds– one a GIA 1.00ct F VS2 and the other an IGI 1.00ct F VS2 that you can go with the one with the better price and the quality will be the same. This similarity has been noted by other researchers. In another study, a data analyst also compared a larger pool of 29 diamonds that had been graded by both GIA and IGI and found that it was impossible to say that one lab was stricter than the other (source).

EGL reports are less popular in the US due to the looser grading standards. There are cases, though, where a customer looking for a specific stone may choose to go with an EGL-graded diamond. If you have the counsel and advice of an honest jeweler on how to interpret an EGL report versus other reports, an EGL-graded diamond could be a good purchase, depending on the situation. As was noted before, a good lab doesn’t mean the diamond is good, and a shady lab doesn’t mean the diamond itself is bad– it’s all a matter of knowing how to interpret the grades. There may be cases where an EGL-graded stone is the best look, fit, and price for your project (as long as you know to “subtract” a couple grades from the report card when comparing it to stones graded by other laboratories).

There are actually several diamond grading labs with very good reputations that weren’t included in this particular study. AGS uses slightly different terminology than GIA, using numerical values for the 4Cs, so, by that nature, doesn’t lend itself as easily to a side-by-side comparison with the letter-value scales that other labs use. Many gemologists, however, respect this lab and others as appropriately stringent. The DeBeers Group Institute of Diamonds also provides grading and report services that are widely respected within the industry. There are also labs that provide specialty reports, like GCAL which certifies lab-grown diamonds within the bounds of the respectable industry standards. 

A cut above the rest?

When looking for a diamond, sometimes marketing techniques can make a buyer think that the diamonds at these stores have cut grades that are somehow above the rest. A few popular retailers use jargon to imply that they offer diamonds with cuts beyond “excellent,” but “excellent” is literally the best possible cut grade on a GIA report. Some retailers refer to their cuts as “super-ideal,” “Astoria excellent,” or some other trademarked term. They may even laser etch these brand-names of cuts into the girdle. Anyone can trademark a proprietary brand, but don’t be fooled into thinking that branding has gemological value. 

These “super” cut grades are simply marketing ploys that have nothing to do with the cut grade assigned by any lab. A GIA report will not contain a trademarked superlative as the cut grade. When it comes to a GIA diamond report, there is no such thing as better than excellent (AGS and IGI use the term “ideal” to describe their highest cut grades, which are equivalent to GIA’s “excellent”). Even when brands promote these super-cuts, the reports will tell the truth– many of these “super” grades are simply a GIA “very good” when you look at the report. 

The best advice is that when it comes to grading, look at the lab report alone. If the seller calls the cut “super-” anything, or if their name for the cut grade is trademarked or sounds like the title of a romance novel, it’s a gimmick. We believe this type of practice is fundamentally dishonest because it tries to deceive customers into confusing trademarks with the independent laboratory reports. Independent laboratory report results must be presented clearly, without misleading and inflating jargon, to ensure that consumers can make educated purchases and trust that the diamonds they purchase are exactly as described. 

Remember, you’re buying a diamond, not a report

It is incredibly important for labs to be reputable and for you to be educated and informed about the diamond you’ve chosen– whether it’s to express your commitment to your significant other, to celebrate a milestone, or a meaningful choice of self-expression, you deserve honesty and transparency in your purchase. 

At the end of the day, however, it can be easy to get too bogged down in the details of reports, percentages, measurements, and grades. The report is assurance that you’re purchasing what you intended to purchase, but it’s not the item itself. The diamond is the most important thing– the way it sparkles, how you feel when you wear it, how it will work for the piece of jewelry you’re imagining. Going to a trusted jeweler to get help making the decision is the easiest way to keep from getting too bogged down in the process. Your jeweler can show you important differences as you make comparisons during your decision process and can ease your mind by answering questions knowledgeably. 

If you’re interested in a piece of custom diamond jewelry, created especially for you, contact a member of our design team today. Our knowledgeable and skilled team can confidently answer questions and help you choose your diamond– all in a comfortable doubt-free, gimmick-free bespoke environment.