The first thing most consumers learn about diamonds is that diamond quality and prices are dependent on the 4Cs: color, cut, carat and clarity. But even though this is at the core of how we value diamonds, it’s all to easy for us to just accept what a jeweler tells us about a diamond. So today I’m going to discuss how diamond grading can be subjective and help you understand how the industry has evolved in regards to diamond grading and what you need to look out for as you enter the world of diamond shopping.

Before the 1950s, diamond grading was an informal process where diamond wholesalers, cutters, and retailers determined the grading of diamonds for themselves. This all changed in 1953, when the GIA (Gemological Institute of America) established an independent laboratory and created consistent standards for the grading of diamonds. Soon after, many the other labs began to establish themselves in the diamond business as well and before long the diamond trade was transformed. Today you might hear trade members say that consumers shop for lab reports rather than shop for diamonds.

Unfortunately there are still too many jewelers who continue to spread a myth that all diamond grading certificates are created equal and it doesn’t really matter who does the grading or which lab does it because the diamond has the same grade. The truth is, while some parts of diamond grading are indeed objective such as the weight of the stone, the angles and the dimensions, as well as the type and location of the inclusions; a large part of diamond grading is also very subjective.

This is important because a difference of just one color or clarity grade can translate to as much as 25% in the price of a diamond. Some credit should be given to the trade for cracking down on some labs who use GIA terminology but do not grade diamonds using GIA standards, but unfortunately consumer over-reliance on any piece of paper continues to be a problem.

Subjectivity in Color Grading

Color is graded with the unset stone facing down so its table facet is on a flat surface in order to minimize the light return that obscures the true body color of the diamond. To make the process even more uniform, the diamonds are graded under highly controlled conditions with standardized lab lighting at specified color temperatures and a white background.

The diamonds are graded for color against a set of master stones. Master stones are carefully assembled comparison diamonds and a diamond’s color grade is awarded depending on which master stone they most resemble. So let’s say you have two diamonds that are both colorless. If you compare them side by side, under the best lighting and in a dark room with the stones upside down and against a white background. You might see a relative difference between the two diamonds IF you have exceptional vision.

A trained color grader under these conditions may notice that one diamond is slightly whiter than the other. Next he or she will compare them against the master grading stones. One of them is an exact match for the F color master stone, but the other one is just a shade whiter and isn’t quite an exact match.

However, when compared to the E master stone it’s not a match either. Instead, the stone falls somewhere between the E and the F master stones. Should the grader declare that stone an E or an F? Good question, right?

So, they squint and squirm and stare until they decide that the stone is just a hair closer to the E color than the F color master, and then decide that it should be graded as an E. Now, the next grader who evaluates those exact same two stones might disagree, and instead of deciding that a stone is an E at the bottom of the E color range as the first grader did, a decision is made that the diamond is an F color in the upper levels of the F color range.

Each grader has followed the standard procedure and is telling it as they see it. There is no deception involved, and they are both correct. This grading subjectivity is further complicated by the fact that, as you move higher up the color and clarity scales, each color grade gets increasingly more restrictive so the tint tolerance that determines the difference between the E and the F color grades is much smaller than that between the I and the J color grades. This is one of the huge challenges the trade faces when it comes to diamond grading.

Subjectivity in Clarity Grading

Unlike color grading, clarity is graded with the unset stone table facet facing up. The diamonds are viewed by eagle-eyed graders under 10x magnification under standardized lighting conditions. The visible inclusions are plotted for location and type and the polish and symmetry of the facets are also noted.

The size, location and type of inclusions that are tolerated in the SI range are much less restrictive than in higher, less included clarity ranges. So let’s say you have a diamond that has twinning wisps in it and by itself it warrants an SI1 clarity grade. If we add a tiny feather inclusion on the table of that diamond, that feather may not affect the grade of the stone at all.

The diamond may still be graded an SI1 even though you’ve added an inclusion to it. Why? Because the SI1 range is a large one, and stones with multiple inclusions are often seen in that grade.

However, if you take that same feather and add it to the crown facets of an FL stone it will be enough to drop the stone down three grades all the way down to a VVS2! And if you move the feather a millimeter and put it under the table facet then you might now be further down to a VS1. Again, this is purely because the FL-VVS ranges are small ranges, whereas the SI range is enormous in comparison.

Grading Disclaimers

GIA and AGSL (American Gem Society) are two of the most reliable and consistent labs in the world and they are widely considered to be the two most trusted sources of diamond grading in North America. But even these two top-tier labs do not guaranty the grades that they issue on their diamond grading certificates. Considering how much of a diamond’s price is dependent on the lab assigned grades, most shoppers are understandably startled to find this out.

In fact, both issue standard disclaimers specifically stating that if the stone is graded under different conditions at a different time then the grades awarded to a stone may have a certain degree of flexibility.

Here is the GIA disclaimer found here with the important parts bolded:

“A GIA Report is not a guarantee, valuation or appraisal, and GIA makes no representation or warranty regarding its Reports, the articles described therein or any inscription thereon. A GIA Report contains only the characteristics of an article described after it has been graded, tested, examined, and analyzed (collectively, “examination” or “examined”), using the techniques and equipment used by GIA at the time of the examination. The results of any other examination performed on the article may differ depending upon (i) when, how and by whom the article is examined and (ii) the changes and improvements in techniques and equipment that may have occurred which may enable the examiner to detect, among other things, the use of processes for altering the characteristics of an article which use was previously undetectable by GIA, or alterations which became reversible, even if the process remains undetectable. The trademark, service mark, logo, words, characters or other symbols of an inscription, other than a GIA Report number, or a GIA trademark, service mark or logo, are solely determined by and attributable to the Client for whom the Report was prepared and are neither attributable to nor to be understood as an indication of any determination by GIA.” (emphasis added)

Conclusion

In addition to what I mentioned above, a diamond’s size can also affect how color and clarity is graded. Larger diamonds that are two carat and over trap more color than smaller diamonds so a large diamond with the same color grade as a smaller diamond may appear more tinted to you. And with regard to clarity, larger diamonds have larger facets that result in more noticeable inclusions even if the inclusion itself is exactly the same.

All of these factors come into play when grading color and clarity. And while GIA and AGSL do their best to make sure each and every stone is evaluated under the same conditions, a lot hinges on the eyesight of the graders.

To counteract all of this potential fallibility to a commercially reasonable extent, GIA awards color and clarity grades based on votes by multiple graders. AGS also employs GIA Graduate Gemologists for their grading and follows the same standard of assigning multiple graders to verify the grading of its stones for clarity and color.

Each grader does a blind grading for each stone so no grader knows another grader’s results before they grade the stone. Then the grades awarded are reviewed and compared. If the graders agree as a majority, a grade is assigned. If there is disagreement then the diamond is put through further testing.

So what does this all mean for you?

Well first of all you’ve come to the right place because the best way to protect yourself is to do your own research and get educated about the 4Cs beyond what jewelers are likely to share with you. You can also talk to a diamond expert and/or ask to speak with the in-house Graduate Gemologist at the jewelry store and ask to see his or her credentials.

Whether it is a good or bad thing, the diamond industry has become as much, or more, about diamond lab reports as it is about diamonds. This means lab consistency is paramount when you pick your diamond. The reason why GIA and AGSL graded stones cost more than those graded by less consistent labs is because they protect your investment more by ensuring to the extent commercially reasonable that your GVS2 diamond, if re-graded three years later, doesn’t come back as an H or an SI1.

And that protection is paramount.