Diamond Certification: Is the GIA Reliable?


Summary
Understanding diamond grading reports, often called certificates, is a critical part of diamond buying. These documents provide information about the diamond’s quality, but not all diamond certificates are equally reliable.

We’ll answer some common questions about diamond certification and provide information about different diamond grading laboratories, so you can make an informed decision about your diamond purchase.

Reading time: 7 min 38 sec
diamond certification - engagement ring
Without a grading report, it’s impossible to know this diamond’s color and clarity. Even then, some grading reports can disagree on these qualities. “Engagement Ring,” photo by Ilovebutter. Licensed under CC By 2.0.

What Makes Diamond Certification so Important?

A diamond’s certificate is like its ID. Gemologists can confirm a diamond’s identity through its cutting angles, clarity imperfections, and girdle inscription.

The certificate will also tell you if a diamond is mined or lab-made, or whether it has undergone HPHT or laser drilling treatments. Combined with the Four Cs (color, clarity, cut, and carat), this lets you know the diamond’s quality. Based on that and the diamond’s performance, you can get a very good idea of how much it should cost.

So, diamond certification assures you that the diamond you pay for is the one that you get. It also allows you to compare the prices of diamonds with similar stats.

Should I Buy a Diamond Without a Certificate?

Without a grading report, you could be overpaying for your diamond. Even worse, there’s a possibility that the diamond will be lab-made or has undergone treatments which lower its value. More often, the diamond may have a different color and clarity grade than advertised.

In the end, no one selling a real diamond should protest to having it certified. Simply ask if you could send it to the laboratory before purchasing it. Laboratory grading is inexpensive and well worth the cost if the diamond is over $1,000. Check out the GIA grading services for loose diamonds or the more limited AGS mounted diamond grading report.

diamond certification - old diamond engagement ring
Antique and heirloom diamonds may not have certificates — or at least not one you can find! If you’re paying for it, it’s good to send it to a lab to make sure it’s genuine and to get an idea of its value. “Old Diamond Ring,” photo by Ed Ivanushkin. Licensed under CC By-SA 2.0.

Should I Only Buy a Diamond with a GIA Certificate?

Some believe that only a GIA certificate is good enough. However, many other gemological laboratories provide diamond certification services.

What Information is on a Diamond Grading Report?

Not all reports are the same, but most laboratories will include most or all of the following information in a diamond grading report:

  • Report number
  • Date the diamond was examined
  • Shape
  • Cutting Style
  • Measurements (length, width, and depth, in mm)
  • Carat weight
  • Color grade
  • Clarity grade
  • Cut grade
  • Polish grade
  • Symmetry grade
  • Fluorescence strength and color
  • Notes on clarity characteristics
  • Inscriptions on the girdle
  • Diamond proportions, including:
    • Table size
    • Depth
    • Crown height
    • Pavilion depth
    • Girdle thickness
    • Culet
    • Crown angle
    • Pavilion angle
  • Diagram of diamond clarity characteristics
  • Grading explanation
  • Comments

Some laboratory reports may include results from a Hearts and Arrows viewer, ASET, or Ideal Scope.

The cut proportions and clarity characteristics act as a sort of “fingerprint” for your diamond, allowing others to confirm that it’s the same diamond on your report.

If you’re buying a diamond and wary of the dealer, ask to see the girdle inscription with the report number and confirm the report online. Or, better yet, work with a retailer you can trust!

Grading and Overgrading

When considering diamond certification services from different laboratories, it’s important to consider how each laboratory decides on a grade and whether they may regularly grade more favorably than the most reliable laboratories: the GIA and AGS. Certain labs may generously grade a diamond as one color or clarity grade higher than the GIA. When comparing prices, this diamond may seem like a deal. When you’re aware of how different laboratories assign grades for the Four Cs, you’ll be able to compare prices fairly. Remember, there are no “good deals” in diamonds. But there are “fair deals” with appropriate prices.

While it’s widely known that some laboratories inflate grades, there’s a legal distinction between this and outright overgrading. When there’s a disagreement of two or more color or clarity grades, the laboratory has overgraded it and misrepresented the diamond. In this case, there may be legal repercussions.

Diamond Grading Laboratories

Learn about the different grading standards from the most widely used laboratories so you know what to expect when you buy.

Gemological Institute of America (GIA)

The largest and most trusted gemological laboratory, the GIA diamond grading standards for the Four Cs have become the internationally accepted standard. Their grading is highly consistent and reliable. You can trust their grades and high standards.

American Gem Society (AGS)

Another great option is the AGS. Like the GIA, the AGS provides great consistency with their grading scale. However, they don’t use the same scale to grade diamonds as the GIA does. Instead, the AGS grades color, clarity, and cut on a 0-10 scale, where 0 is the best possible grade. Here’s how the AGS grades line up with the more familiar GIA grades:

diamond certification - comparison of AGS and GIS grades
While most grades line up well, there are some cut quality and clarity grades that don’t have a direct equivalent between AGS and GIA. © International Gem Society.

In addition, the AGS provides a grade based on light performance on certain diamond certificates. Unlike cut grades, light performance grades can provide some assessment for how well the diamond will perform. Light performance grades are particularly helpful for diamonds with fancy shapes, since these shapes don’t receive traditional cut grades.

It’s worth noting, however, that AGS standards on color and clarity are somewhat looser than the GIA’s. For diamonds with borderline color or clarity grades, the AGS will often give them the higher grade, while the GIA would grade them lower. Still, whether a diamond was graded by the GIA vs AGS doesn’t impact its price.

International Gemological Institute (IGI)

Many diamonds receive grades from IGI laboratories, but these grades can be inconsistent, even between US-based IGI NY and internationally based IGI laboratories. When compared with GIA diamonds, IGI diamonds will often have a grade higher on either color or clarity.

Because of this, IGI diamonds are usually priced around 20% cheaper than GIA or AGS diamonds. If you compare the IGI-graded diamond below with the GIA and AGS-graded diamonds above, you’ll notice a significant price difference in spite of similar grades.

Gemological Science International (GSI)

Serving large retail chains in the US, the GSI is another laboratory with looser and more inconsistent standards than the GIA. With less reliability than the IGI, a GSI-graded diamond is best avoided. Again, these diamonds will appear to have lower prices because of the difference between its “true” grades and the ones on its certificate.

European Gem Laboratories (EGL)

Blatant overgrading at EGL resulted in its being de-listed from RapNet and legal action taken against the laboratory. Diamond grades from EGL may be wildly inflated, making the stone look worse than its grade implies.

It’s best to avoid EGL-graded diamonds. Because of their overgrading, you’ll likely be paying too much for a poor-quality stone.

Brand or Store Diamond Grading

Some brands may grade their diamonds in-house rather than sending it to an outside laboratory. While a few are remarkably consistent, such as Tiffany & Co, most have somewhat looser standards.

In addition, some will provide color grades like “G/H” where the diamond could be either color grade. In smaller diamonds, the difference in cost is minimal, and the extra time taken to give a more exact color grade isn’t cost efficient. However, in stones of one carat and above, the difference in cost can be significant. It’s best to have a more exact color grade in these sizes to avoid overpaying.

Which Diamond Certification is Best?

The reliability of GIA and AGS grading makes these grading reports the best in the industry. If you’re worried about overpaying, stick to diamonds with grades from these laboratories.

Where Can I Buy Certified Diamonds?

Online retailers provide some of the best deals in diamonds, and any trusted retailer will provide grading reports with their diamonds. Better yet, many retailers can provide images and video of their wares, letting you choose the one with the best sparkle!

Blue Nile and James Allen have thousands of diamonds to choose from.  Blue Nile’s wares come with GIA diamond certification, while James Allen offers diamonds with certificates from GIA, AGS, and IGI. With the wide selection of engagement ring settings available at James Allen, we recommend their site for diamond engagement rings.

Alternatively, you could create a completely unique ring with certified diamonds through a custom jeweler such as CustomMade. Their experts will help you find the diamond that’s best  for you and place it in a ring full of meaning.

About the author
Addison Rice
A geologist, environmental engineer and Caltech graduate, Addison's interest in the mesmerizing and beautiful results of earth's geological processes began in her elementary school's environmental club. When she isn't writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.
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