Comprehensive Guide to GCAL Diamond Certification Laboratory

This page may contain affiliate links.

  • Home
  • //
  • Comprehensive Guide to GCAL Diamond Certification Laboratory

The Gem Certification & Assurance Lab (GCAL) is an esteemed diamond grading laboratory. They pride themselves on providing unbiased and precise evaluations of natural and lab-grown diamonds.

Unlike its competitors, GCAL issues diamond grading certificates instead of reports. That critical difference distinguishes them from other gemological laboratories because certification assures guaranteed quality.

A photograph of the GCAL Certificate number inscribed on the girdle edge of a diamond as seen through extreme magnification.

GCAL Inscription of Certificate Number.

GCAL's Gemological Services

GCAL offers a broad range of gemological services for the gem and diamond industry, including:

  • Natural diamond grading and certification
  • Lab-diamond grading and certification
  • Diamond cut-quality analysis
  • Fancy-colored diamond grading
  • Colored gemstones grading & identification
  • Cultured pearl grading report
  • Jewelry appraisals for insurance
  • Precious metal testing
  • Photography and Video services

Is GCAL a Legit Gemological Laboratory?

The Gem Certification & Assurance Lab (GCAL) is a reputable independent gemological laboratory. In our experience, their grading standards are comparable with GIA and (the former) AGS Laboratory.

Historically, GCAL holds a smaller market share, but they've gained ground since the AGSL closed in December 2022. The President and founder of GCAL (2001) is Donald A. Palmieri, an internationally respected appraiser specializing in forensic gemology.

GCAL's headquarters is in the 580 Fifth Avenue building in New York City, a hub of the diamond industry. Its ISO 17025 certification status is an impressive quality assurance benchmark reflecting its commitment to excellence.

By all accounts, GCAL is trustworthy and well-known throughout the industry. From our perspective, they're quickly becoming the ones to watch due to the launch of their 8X cut grading and GCAL by Sarine partnership.

GCAL's ISO-17025 accreditation certificate.

GCAL's ISO-17025 Accreditation Certificate.

Is GCAL Diamond Grading Accurate?

GCAL's diamond grading system is world-renowned for its state-of-the-art precision and reliability. Diamond buyers can rely on its accuracy and trust in the inherent value of their purchase.

Consequently, GCAL is the only gemological laboratory that guarantees its grading with a "Zero Tolerance" cash-back policy. That is why GCAL issues diamond grading certificates instead of diamond grading reports. In contrast, the disclaimer on a GIA diamond grading report reads:

"This report is not a guarantee, valuation, or appraisal and contains only the characteristics of the diamond described hereinafter it has been graded, tested, examined, and analyzed by the GIA Laboratory."

Examples of GCAL Diamond Grading Certificates for natural and lab-grown diamonds graded on their 8X Ultimate Cut Grade platform.

Examples of GCAL Certificates.

GCAL vs. GIA Grading Standards

In our experience, GCAL's grading standards are on par with GIA for carat weight, color, clarity, and characteristics of polish and symmetry. That's unsurprising since the industry closely adheres to GIA grading standards to ensure global consistency.

However, there are vast differences between the GCAL 8X and GIA Excellent cut grading platforms. According to GCAL, over 50% of round diamonds submitted to GIA for grading receive an overall cut grade of Excellent.

In contrast, GCAL claims that only 1% of those diamonds qualify for the new GCAL 8X cut grade due to its strict methodology. One reason for the difference is that GIA's proportions guidelines are rather broad by our standards.

From our perspective, GCAL is trying to bridge the gap left behind by the AGS Laboratory's closure. GIA's recent acquisition of AGS ASET might encourage them to up their game in the arena of light performance.

However, we're not holding our breath, given it took them almost a decade to introduce GIA Excellent cut in response to AGS Ideal. Time will tell, but we might be watching the remake of David versus Goliath in the form of GCAL vs. GIA.

GCAL's 8X Cut Grade

The GCAL 8X Cut Grade enables you to confidently select the most beautiful and brilliant diamonds in-store or online. According to GCAL, less than 1% of GIA Excellent cut diamonds qualify for their 8X rating.

Consequently, that estimate coincides with our experience in the niche of diamond light performance. Less than 1% of the annual round production meets our recommended proportions.

Only 0.001% of round brilliant cut diamonds meet our Super Ideal Cut Hearts and Arrows standards. The superior light performance and sparkle factor those diamonds exhibit result from a combination of precise proportions and optical precision.

Proportions diagram for a round brilliant ideal cut diamond, including the essential measurements.

Round Diamond Proportions Diagram.

The GCAL 8X Ultimate Cut Grading System

GCAL's proprietary 8X cut grading system accounts for all aspects of diamond cut quality. Understanding the differences between GCAL and GIA's approach is essential to appreciate the distinction fully.

Both GCAL and GIA consider polish, proportions, and symmetry in their cut grade assessment. However, GCAL also accounts for light performance and optical excellence, which the GIA does not include in its standard report.

The GIA does offer an optional ASET-based AGS Ideal report for an additional charge. Unfortunately, most diamond dealers refrain from paying for an optional light performance report likely to expose their diamonds' faults.

The New Standard in Diamond Grading (Video)

This video introduces the new GCAL 8X Ultimate Diamond Cut Grade Guaranteed Certificate. The Gem Certification & Assurance Lab of NYC is world-renowned for its accurate and consistent grading platform.

Most gemological labs base their overall cut grade on three factors, polish, symmetry, and proportions. The former AGS Laboratory raised the bar by using its Angular Spectrum Evaluation Tool as a determining factor. GCAL is taking things to the next level by focusing on eight essential characteristics.

Nice Ice vs. GCAL Proportions Guidelines

A diamonds' proportions dictate the volume of light return and the balance of brilliance and dispersion. We strictly adhere to the middle of the ideal-cut range, well-known as the sweet spot.

In contrast, GCAL's parameters are slightly broader but within a tolerance of our preferred range. Nevertheless, their proportions guidelines are significantly narrower than GIA's, making obtaining the higher cut grade more difficult.

Proportions Guidelines:

Nice Ice


Table % :

53 - 58%

54.0% - 58.0%

Depth % :

59 - 61.8%

59.8% - 62.2%

Crown Angle :

34.3 - 35.0°

34.0 - 35.0°

Pavilion Angle :

40.6 - 40.9°

40.6 - 41.00°

Lower Girdle Facet Length :

75 - 80%

75 - 80%

Star Length :

45 - 55%

45 - 55%

Girdle Thickness :

Thin to slightly thick, faceted

Thin to slightly thick, faceted

Culet Size :


None - Very Small

We suggest strictly adhering to our recommended proportions for the best light performance. However, we also acknowledge that it's essential to evaluate each diamond based on its merits and account for personal preferences.

GCAL by Sarine

Acknowledging that the Gem Certification & Assurance Lab (GCAL) and Sarine Technologies are separate entities is essential for clarity (pun intended). Sarine is a well-known manufacturer of diamond technology solutions, including the proportions measuring devices used by most gemological labs.

GCAL and Sarine have formed a new partnership to automate the grading process to improve accuracy and consistency. The combination of GCAL's uncompromising grading standards and Sarine's AI-based color and clarity grading technology is revolutionary.

GCAL by Sarine uses advanced imaging and lighting systems to examine diamonds similarly to live gemologists. Then, it relies upon machine learning algorithms to analyze the images and determine the color and clarity grades.

Simultaneously, GCAL by Sarine provides a verifiable record of the origin of your diamond. According to GCAL, its traceability solution verifies a diamond's origin, journey, and transformation from rough to polished state.

An illustration demonstrating how GCAL by Sarine uses AI to consistently grade Diamond 4Cs characteristics accurately.

GCAL by Sarine AI Grading Technology.

The PROS of GCAL Certification

Assurance of Authenticity

Every GCAL-certified diamond comes with a guarantee of its authenticity, quality, and value based on the 4Cs. Their rigorous testing procedures ensure you're buying a genuine diamond with an accurate description of its characteristics.

Accurate Grading

Like most laboratories, GCAL adheres to GIA grading standards for color, clarity, and characteristics like polish and symmetry. That makes sense because the industry adopted those standards in 1954 and relies upon them to maintain accuracy globally. However, GCAL goes one step further and certifies its grading with a "zero tolerance" cash-back guarantee.

Comprehensive Analysis

GCAL's grading system is world-renowned for its precision and state-of-the-art technology. When a diamond receives a GCAL 8X cut grade, you can trust that it will be stunning.

Verify Your GCAL Certificate Online

You can Verify your GCAL Certificate online if you have the report number. The verification page features a color copy of the certificate and large high-resolution versions of the images. 

Go ahead and take it for a spin. Click on this Optical Symmetry photograph to see the GCAL Certificate #331230109 verification page. We're certain you'll be impressed with the extent of in-depth details GCAL provides as part of their 8X Cut Grade analysis.

If applicable, GCAL also provides details about your diamonds' journey when verifying a GCAL certificate online. In this case, they provide a scan of the diamond rough, a 3D model of the planning stage and polishing process, a proportions diagram, a Gemprint® fingerprint, and a photograph of the inscription on the girdle edge.

Synapsis of in-depth details GCAL certificate verification page, including optical brilliance, symmetry, and hearts and arrows images.

Click to Verify GCAL Certificate ID: 331230109

Elements of GCAL Diamond Certification

Every diamond's unique features are meticulously cataloged, including carat weight, color, clarity, and cut quality. The report features a high-resolution image of the diamond, enabling you to identify the inclusions and evaluate how evenly light reflects.

Additionally, there are photomicrographs of the crown and pavilion views and a representation of the diamond's actual size. GCAL also provides the following images to support their assessment of diamond cut quality:

  1. 1
    Optical Brilliance
  2. 2
  3. 3
  4. 4
    Optical Symmetry
  5. 5
    Hearts and Arrows

The certificate also features a photograph of the inscription on the girdle edge for identification purposes. Consequently, you can register your diamond's inscription with GEMTRACE™ to create a record of ownership.

Ethical Standards

GCAL appreciates that you are relying on the accuracy of their grading to make a significant financial decision. Only three diamond grading labs in the world are ISO 17025 accredited, and GCAL is one of them. Their instruments are calibrated and verified daily by highly trained expert staff.

Merits of GCAL Over Other Labs

GCAL stands out for its commitment to transparency, accuracy, and innovation. Here's why:

  1. 1
    Assurance of Quality: GCAL maintains the lab's integrity by strictly adhering to ISO 17025 grading standards that ensure consistent quality.
  2. 2
    Visual Performance: Using state-of-the-art technology, GCAL analyzes the diamond's optical brilliance and symmetry.
  3. 3
    Zero Tolerance Policy: Each GCAL-certified diamond has a cash-back guarantee, underlining its commitment to total satisfaction.

How to Interpret GCAL Certification

Take a look at this GCAL Certificate for a natural round brilliant cut diamond; it provides everything you need to make an educated decision:

GCAL natural diamond certificate showing characteristics of the 8X Ultimate Cut Grade (sample).

GCAL Diamond Certificate 8X Ultimate Cut Grade

Images provided by GCAL for judging diamond light performance and optical precision on their 8X Ultimate Cut Grade platform.

GCAL Images for Judging Light Performance Factors.

  • 4Cs Grading: Clearly stating the characteristics, such as carat weight, color, clarity, measurements, etcetera.
  • Gemprint® This "Fingerprint" shows your diamond's unique reflection pattern.
  • Laser Inscription: Such as the diamond certificate number.
  • Photomicrographs: High-resolution photographs of the crown and pavilion sections.
  • Optical Analysis: Insights into the diamond's brilliance and fire.
  • Proportions Diagram: An accurate to-scale representation of the proportions.

Natural and Lab-grown Diamond Grading

Whether you prefer natural or lab-grown diamonds, you can rely on the consistency of GCAL's strict grading standards. Consequently, GCAL offers 8X cut-grade reports for natural diamonds and their lab-grown counterparts.

The distinguishing difference between the reports depends on the diamond's origin, which appears in the upper left quadrant. In other words, the report will state whether it's for a natural or lab-grown diamond.

Additionally, the abbreviation "LG" appears at the beginning of the inscription on the girdle edge to indicate the diamond is lab-grown. For example, the notation "GCAL LG320862243" designates that the diamond is lab-grown.

The lab-grown diamond certificate shown here features photographs of the inscription and the words "Lab Grown" for verification purposes.

GCAL Lab-grown diamond grading report for the 8X Cut Grade featuring an inscription indicating the lab-created origin.

GCAL Lab-grown Diamond Report.

What is a GCAL Diamond?

GCAL is an independent gemological laboratory that grades diamonds, colored-gems and provides jewelry appraisals. They do not manufacture or polish diamonds; therefore, there is no such thing as a GCAL Diamond.

However, GCAL-graded diamonds are available in various shapes, sizes, and qualities. Under those circumstances, it's irresponsible to say that GCAL diamonds are high quality, and the same principle applies to GIA-graded diamonds.

Evaluating each diamond's characteristics carefully is essential to ensure your complete satisfaction. Remember that only 1% of round brilliant cut diamonds meet our proportions guidelines. Fewer meet our standards for Hearts and Arrows super ideal cut diamonds.

Rendering of a round brilliant cut diamond exhibiting a pattern of eight hearts due to precision polishing and facet alignment.

Hearts Pattern Visible in this GCAL 8X-graded Diamond.

Summary of our GCAL Review

The Gem Certification & Assurance Lab (GCAL) is an independent gemological laboratory of the highest standard. It provides you with a guaranteed certificate clearly stating the quality of your diamond.

GCAL's certification, backed by rigorous ISO-certified grading standards, provides the in-depth details necessary to make an informed decision. Although they hold a smaller market share than the GIA, we anticipate them becoming a major influence in diamond performance grading.

Its recent introduction of the 8X Cut Grade and GCAL by Sarine is bound to take the industry by storm. We're certainly impressed and look forward to seeing what new developments GCAL introduces next.

Feel free to submit the details of any GCAL-graded diamonds you are considering for evaluation via our Free Diamond Concierge Service. We'll review the details and answer any questions you have about the optical brilliance, symmetry, and Hearts & Arrows images.


Can GCAL be trusted?

GCAL has established a significant reputation in the diamond industry for its rigorous and transparent certification processes bolstered by years of experience and cutting-edge technology.

Is GCAL a reputable laboratory?

The Gem Certification & Assurance Lab (GCAL) is a reputable laboratory recognized in the diamond industry for its rigorous and transparent certification processes.

Are GCAL diamonds high quality?

GCAL is an independent and impartial gemological laboratory providing the industry with natural and lab-grown diamond grading. As such, they do not manufacture or polish diamonds, and there is no such thing as a GCAL Diamond.

Does GCAL grade lab-grown diamonds?

The Gem Certification & Assurance Lab (GCAL) grades natural and lab-grown diamonds using the same precise standards and state-of-the-art technology. GCAL's 8X Ultimate Cut Grade platform provides in-depth analysis, including Optical Brilliance, Fire, Scintillation, Optical Symmetry, and Hearts & Arrows images.

Super Charge Your Diamond Buying Skills:

Follow the Steps in The Nice Ice® Diamond Buying Blueprint™ and Unlock the Secret for Maximizing Sparkle Factor and Light Performance. These are the Tips & Tricks from the back office of Nice Ice Diamonds.