Diamond Certification and Grading: Everything You Need To Know

Basics

A diamond certificate (or grading report) is the document of authority for all of its value-setting “Cs.” You do not want to buy a diamond that’s Over-Graded – because you’ll overpay – so it’s important to choose diamond certification that follows strict, industry-accepted international standards.

PriceScope Pointers

  • The GIA issues the document of choice for high-value, internationally-traded natural diamonds.
  • The AGS issues the document of choice for diamonds with superior cut-craftsmanship.
  • The IGI and GCAL are highly regarded for natural diamonds and issue the documents of choice for Lab-Grown Diamonds.
  • Avoid diamonds graded by EGL, known for Over-Grading, as explained below in Diamond Certification Analysis.

Before going on: Check out the PriceScope Diamond Buying Guide

Basics-1 | Diamond Certification Described

A diamond’s certificate (or grading report) is issued by an independent diamond grading laboratory. It’s an assessment of the diamond’s 4Cs: Carat weight, measurements in millimeters and judgments involving color, clarity, and human craftsmanship. Many grading reports include a drawing of the diamond with its physical proportions and a plotted clarity diagram of key characteristics. Some grading laboratories publish supplemental standardized photos and videos online.

diamond certification - Gemologist using a gemstone grading microscope. Photo courtesy of IGI.
Photo courtesy of IGI

Note: The word “certificate” describes an official attestation. This is not what most laboratories provide. They issue “grading reports” with fine print disclaiming those grades as opinion only. For the record, GCAL and AGS are the only top-tier laboratories offering literal diamond certification.

Basics-2 | Diamond Certification: Let’s Get Practical

For loose diamonds: GIA, AGS, IGI and GCAL are all well established top-tier laboratories. They have different strengths, described below in Diamond Certification Analysis. For any of their grading reports, you can rely on the following:

A. Carat Weight is Universal

Carat weight is a standardized measurement. A diamond’s carat weight will be the same at any top-tier laboratory, reported to two decimal places.

B. Color and Clarity Grades are Standardized but Subjective

Top-tier laboratories use strict, industry-accepted international standards for diamond color and clarity grading, including calibrated master-stone sets between locations to ensure consistency. With that said, diamond color and clarity occur on a sliding scale. A diamond sitting directly on the border of two grades may come out either way, depending on the subjective opinion of the gemologist making the judgment.

C. Cut Grades are Wildly Variable

The various laboratories approach diamond cut quality assessment and standards differently. This is important to understand, especially when choosing a diamond online. Read our section on diamond cut quality for more information.

PriceScope Pointer

Be sure to read about Diamond Cut Quality before making a decision. You may not need super ideal cut-quality, but you definitely want to avoid cutting that makes the diamond look smaller, either physically (small spread for weight) or visually (it goes dark at the edges). Diamonds of the same weight don’t always look the same size

Basics-3 | Real World Information

If you have shopped for jewelry in mall-based chain or department stores, you may have been shown grading reports. Certain Department Store reports should not be confused with loose diamond grading reports. They are mass-produced for multiple pieces and are not nearly as specific, strict, or expensive as stand-alone diamond certification for loose diamonds issued by top grading laboratories.

diamond certification - Ring sitting inside a department store jewelry counter
Credit: Brooks Leibee on Unsplash

PRACTICAL ANALOGY: Combo Meal versus À La Carte

For daily-wear pieces at economical prices, those Department Store reports work nicely. Like a combo-meal, they inexpensively provide information on all a jewelry piece’s gemstones, metal content, etc. in a simple and affordably priced way. Alternately, a diamond costing hundreds or thousands of dollars by itself should be treated à la carte, accompanied by its own loose diamond grading report from a top-tier laboratory.

Basics-4 | Can I choose Diamond Certification online with confidence?

YES.

 Successful online sellers like our recommended PriceScope vendors offer diamond certification from top-tier laboratories and back up those grading reports by offering liberal inspection periods and free returns.

  1. Color and clarity grading are subjective so tolerances among labs vary – even between a single lab’s various locations – but the accepted standard among reputable institutions is +/- one grade.
  1. Many sellers additionally provide their own videos and images to back up the information you’re getting in the diamond grading report.
  1. Additionally, some top-tier diamond certification laboratories now offer standardized imaging services with calibrated white balance, filtered lighting and fixed focal-depth. Videos and images of diamonds made in these standardized conditions may be compared head-to-head, between sellers, and are a sales-neutral extension of independent grading. Read about this below in Diamond Certification Analysis.
  1. Ask the seller directly: If you have questions beyond what a diamond grading report and supplemental videos and images can communicate, pick up the phone, chat or email and get in touch with the vendor. It’s in their best interest to communicate transparently with you. After all, they don’t want the expense of shipping a diamond, only to have it returned on their dime.
  1. Get quick answers to any question now: Ask our community of unbiased independent helpers.

 


Intermediate Diamond Certification

Analysis

Diamond certificates (aka grading reports) are issued by independent grading laboratories. In this section we will provide information on the most recognized diamond grading institutes operating in the United States and, in some cases, around the world.

Analysis-1 | Diamond Certification: Gemological Institute of America (GIA)

GIA diamond grading laboratory
Photo courtesy of GIA

Established in 1931 by Robert Shipley, the GIA is the world’s foremost authority on diamonds, colored stones, and pearls. A public benefit, nonprofit institute, the GIA is the leading source of knowledge, standards, and education in gems and jewelry. As the oldest and most widely recognized gemological institute, the GIA has long set the standards by which other laboratories are measured.

PriceScope Pointer: The GIA is the world’s most recognized grading institute. If you were buying a million dollar diamond at a Sotheby’s auction you could expect it to be accompanied by a GIA report.

GIA Diamond Grading Report

The GIA’s diamond grading report provides a 4Cs assessment with a plotted clarity diagram. The GIA only provides a cut-grade for round brilliant diamonds. All other shapes are only graded for polish and symmetry, not for cut.

diamond certification - GIA Diamond Grading Report

GIA Diamond Dossier

The GIA Diamond Dossier is available for a lower fee and frequently accompanies smaller diamonds. It has a 4Cs assessment but no clarity plot, so laser inscribing the GIA report number is a required and included service.

diamond certification - GIA Diamond Dossier

GIA Diamond eReport

The GIA eReport appears online with 4Cs assessment and a standardized face-up diamond image.

diamond certification - GIA Diamond eReport

GIA Laboratory Grown Diamond Report and Dossier Report (Digital only)

Starting in 2020 the GIA began issuing a Laboratory Grown Diamond Report and Dossier Report digitally, with full 4Cs assessment. The dossier report has no clarity plot. Laboratory grown diamonds will have their girdles laser inscribed with the term “Laboratory Grown” along with the GIA report number.

diamond certification - GIA Laboratory Grown Diamond reports

Analysis-2 | Diamond Certification: American Gem Society (AGS)

AGS diamond grading laboratory
Photo courtesy of AGS Laboratories

In 1934 Robert Shipley established the American Gem Society (AGS) as America’s moral and ethical society for jewelers. In 1996 the AGS opened its own laboratory to serve demand for higher standards in the specific area of cut-craftsmanship. The AGS Laboratories pioneered the “Ideal” cut grade (aka AGS Ideal or AGS Triple Zero). They improved on this in 2005 with the introduction of the first scientifically reviewed and diamond-specific performance metric in the diamond industry. They are one of two top-tier laboratories offering cut quality and performance assessments for certain fancy shapes.

PriceScope Pointer

The AGS is best known for the strictest cut-craftsmanship and optical performance standards. Their Platinum Report is the certificate of choice for diamond brands renowned for top cut-quality.

AGS Platinum Reports

The AGS Platinum DQD (left) and Proprietary DQD (right) are the flagship reports of the American Gem Society. They have 4Cs assessment, a plotted clarity diagram, and diamond-specific “ASET” imprints proving 3D light performance levels, which you can read about in our section on cut quality.

diamond certification - AGS Platinum Reports

Platinum Documents are available for round brilliant, princess, oval, emerald and cushion-shaped diamonds.

AGS Supplemental Information Online: “Only My Diamond”

For an additional fee, AGS offers supplemental information online. The Only My Diamond platform stores a grading report PDF, along with further analysis, a standardized video of the actual diamond and a number of computer generated images (CGI) generated from the diamond’s 3D scan.

diamond certification - AGS Supplemental Only My Diamond screenshot

AGS Diamond Quality Certificate

The AGS Diamond Quality Certificate is more than a grading report. It comes with a guarantee of authenticity and accountability for the diamond’s grade. It includes all features of the AGS Platinum reports above. This document is available only through AGS retail jeweler members.

diamond certification - AGS Diamond Quality Certificate

AGS Diamond Quality Report

The AGS DQR (left) is offered to manufacturers who prefer a lighter 2D proportions-based cut grade which mimics the GIA system. It was developed in response to manufacturers who could not understand the 3D Platinum system. It is less strict and not diamond specific. The AGS Gold DQR (right) comes with an assessment of polish and symmetry only, with no cut grade reported.

diamond certification - AGS Diamond Quality Report

AGS Archived Report Formats

See the AGS Document Library for alternate report formats, including 3-stone and 5-stone collections and reports which have been archived since their metrics have evolved.

Analysis-3 | Diamond Certification: International Gemological Institute (IGI)

IGI diamond grading laboratory
Photo courtesy of IGI

Established in 1975, the IGI is the largest gemological organization of its kind, with 18 laboratories and eight schools of education around the world. The IGI serves a broader range of end consumer buyers than any other gemological laboratory, issuing reports for finished jewelry, in addition to natural and lab grown diamonds, colored stones and identification and appraisal services. The IGI was the first laboratory to grade “Hearts and Arrows” diamonds and pioneered the full grading of Lab Grown diamonds in 2005 – gaining more experience in that area than any other gemological institution.

PriceScope Pointer: The IGI established itself as the world leader in Lab Grown Diamond grading starting in 2005 and is highly regarded for their “Hearts and Arrows” grading across China and India.

IGI Natural Diamond Report

The IGI’s natural diamond grading report provides a 4Cs assessment with a plotted clarity diagram. The IGI only provides a cut-grade for round brilliant diamonds. All other shapes are only graded for polish and symmetry, not for cut.

Read about the IGI Diamond Report.

IGI Hearts and Arrows Diamond Report

The IGI Hearts and Arrows report is associated with Excellent-Ideal cuts of superior quality. The report provides 4Cs assessment, with diamond-specific micrographs showing Hearts and Arrows quality.

Read about the IGI Hearts and Arrows Diamond Report.

IGI Laboratory Grown Diamond Report

The gold standard for lab grown diamonds, the IGI Lab Grown Diamond report provides 4Cs assessment, a clarity plot, and standardized diamond photo. It is offered with or without Hearts and Arrows assessment.

diamond certification - IGI Laboratory Grown Diamond Report

IGI Jewelry Identification Report

The IGI Jewelry Report provides all gemstone and mounting specifics, as well as clear standardized photos showing details of craftsmanship that may not otherwise be visible. More complex than the analysis of loose gemstones, IGI’s expertise in the analysis and documentation of finished jewelry items is unrivaled anywhere.

See samples of the IGI Jewelry Identification Report

Analysis-4 | Diamond Certification: Gem Certification and Assurance Lab (GCAL)

GCAL diamond grading laboratory
Photo courtesy of GCAL

Established in 2001, the GCAL is the only lab regularly issuing guaranteed diamond “certificates,” rather than grading reports with legal disclaimers. The GCAL focuses on diamond cut quality assessment, using a copyrighted diamond-specific performance assessment method, as well as providing a unique diamond fingerprint known as Gemprint. The GCAL takes and publishes standardized technical photos and videos online, is one of two top-tier laboratories offering cut quality and performance assessments for certain fancy shapes and is the world’s only only ISO 17025 Accredited Forensic Gem Laboratory.

PriceScope Pointer: The GCAL is best known for specializing in Lab-Grown Diamond grading, high quality, standardized photo and video services, cut quality analysis and issuing a true diamond “certification.”

GCAL Guaranteed Diamond Grading Certificate

The GCAL Diamond Certificate has a 4Cs assessment, Gemprint diagram and Photomicrographs. It also comes with a diamond-specific Light Performance Profile indicating optical brilliance, optical symmetry and Hearts and Arrows (optional), which you can read about in our section on Cut Quality.

diamond certification - GCAL Guaranteed Diamond Grading Certificate

GCAL Guaranteed Lab-Grown Diamond Certificate

The GCAL Lab-Grown Diamond Certificate has the features of the Diamond Grading Certificate but is framed in a different color and indicates lab grown origin and growth-method.

diamond certification - GCAL Guaranteed Lab-Grown Diamond Certificate

GCAL Supplemental information online: Video and Photos

For an additional fee, the GCAL offers additional services. These include Gemprint, a non-invasive, positive identification technology for each diamond which has been used by the FBI and Canadian Government, along with independent, standardized diamond photography and videography.

diamond certification - GCAL Supplemental information online: Video and Photos

Analysis-5 | Diamond Certification: European Gemological Laboratories (EGL)

For many years overseas EGL locations over-graded diamonds. Over-grading occurs when a laboratory consistently issues better color or clarity grades for diamonds than they would normally according to strict, industry-accepted international standards. The practice became egregious enough that in September, 2014, all EGL-graded diamonds were delisted and removed from the world’s largest trading platform.

“The Rapaport Group is opposed to the misrepresentation of diamond quality. The over-grading of diamonds is an unfair practice that destroys consumer confidence and the legitimacy of the diamond industry… The diamond trade must prioritize the protection of consumers above profits.”

diamond certification - 2014 article stating RapNet will delist EGL graded diamonds

EGL-graded Diamonds Removed from PriceScope

Soon after The Rapaport Group came to this conclusion, PriceScope also made the decision to remove all EGL-graded diamonds from our search engine in the interest of consumer protection.

PriceScope Pointer

Buyer beware: Certain EGL locations are infamous for famously over-grading diamonds, in some cases by 3-4 grades, allowing unscrupulous sellers to overcharge consumers.

Our Advice

In any situation where an EGL graded diamond is being considered for purchase, we recommend the buyer hire his or her own gemological expert to analyze and accurately grade the diamond according to strict, industry-accepted international standards.

Analysis-6 | “Department Store” Laboratories

Ready-to-go diamond and gemstone earrings, pendants, bracelets, cocktail-rings and daily-wear jewelry offered over the counter at mall-based chain and department stores may be supported with “certificates” from a grading laboratory. That documentation is commissioned by the store selling the merchandise and is often provided by the laboratory which submitted the lowest bid for the service.

With that said: Several top-tier laboratories issue finished jewelry reports. Logically, the laboratories engaged in the highest standards for loose diamond grading are also likely to maintain the highest standards when grading finished jewelry.


Advanced Diamond Certification

Evaluation

Evaluation-1 | What is Standard Deviation?

When grading color and clarity reputable gemologists use a set of strict, industry-accepted international standards established by the GIA in the 1950s. Top-tier laboratories and appraisers use calibrated master color stone-sets and uniform clarity standards to ensure a baseline of uniformity lab to lab and location to location.

With that said, no two diamonds are alike. Color and clarity occur on a sliding scale and a diamond sitting directly on the border of two grades may come out on one side of the other, depending on the subjective opinion of the gemologist making the judgment.

To that end, a standard deviation of +/- one grade is deemed acceptable among professionals, should such a deviation occur. However, over a laboratory or appraiser’s ongoing body of work, such deviations should occur in both directions and should never be egregious.

Evaluation-2 | What is Over-Grading?

Over-grading occurs when an appraiser, laboratory or seller continually promotes diamonds as having better color or clarity grades than they would normally receive according to strict, industry-accepted international standards.

For example, a person stating that a diamond has “F color, VS1 clarity” where top-tier laboratories or appraisers would collectively judge it to have H color, SI1 clarity – is Over-grading that diamond.

Diamond overgrading

Why Over-Grade?

Imagine that Simple Sam is shopping for a diamond. “Honest Abe Jewelers” only sells diamonds graded by top-tier laboratories. Simple Sam is considering these two diamonds from Honest Abe. He really wants the F color, but it’s stretching his budget.

  • 1.00 carat F – VS2 Ideal cut for $9,000
  • 1.00 carat H – VS2 Ideal cut for $7,000

“Terrible Herb Jewelers” says he can make Sam a better deal:

  • 1.00 carat F – VS2 Ideal cut for $8,000*

Sam believes this is a no-brainer and buys the 1.00 carat diamond from Terrible Herb. Unfortunately, nobody told him about over-grading so he didn’t end up with a diamond graded by a top-tier lab.

What happened? 

*Sam paid $8,000 for a diamond that would have been graded H – SI1 by a top-tier lab. So, not only did he fail to achieve his color goal… he paid $1,000 more for a diamond with lower color and clarity than Honest Abe was offering him for $7,000. Terrible Herb was even rewarded by Sam’s lack of education, paying his diamond supplier far less for that misrepresented, over-graded diamond than Abe would have paid his supplier for correctly graded diamonds.

It’s highly possible that down the road, a family member will inherit the diamond and have it appraised only to find out Sam was gouged by an unscrupulous seller.

Get quick answers to any question now: Ask our community of unbiased independent helpers.

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