What Is NGTC? A Deep Dive into China's Only Trustworthy Gem-Testing Authority
China is home to hundreds of businesses operating under names like "gem testing" or "gem certification," but only a small number carry genuine credibility. Chinese state media has repeatedly reported on certificate fraud in the jewelry sector — from forged inspection reports to sellers offering "certificates with no physical inspection required" for as little as a few RMB. Certificate fraud is one problem. A quieter risk is grade inflation: some smaller labs bump a natural diamond's clarity or color up by one or two grades — turning a VS2 into a "VVS2," for example — to help close a sale. In the natural diamond market, that two-grade gap alone can translate into a meaningful price difference that's invisible to the naked eye. Among the many testing bodies operating in China, NGTC (the National Gemstone Testing Center) is one of the few with genuine government backing, and it's widely regarded within the industry as comparatively trustworthy. This guide, compiled by the MadisonDia team, walks through NGTC's background, what it actually tests, and how to read a certificate with confidence.
China's Gem Testing Institutions: A Certificate Doesn't Always Mean Protection
The barrier to entry for gem testing businesses in China is relatively low, and some operators skip the standard submit-inspect-verify workflow entirely. China's State Administration for Market Regulation has run repeated crackdowns on the testing and certification market, but given the sheer number of operators, buyers still need to do their own diligence on where a certificate actually comes from.
Putian, Fujian — Fabricated Gold Testing Report
In 2024, a gold and jewelry testing center was investigated by local market regulators after issuing a fabricated testing report for gold coins.
Guangzhou — Forged Credentials and Signatures
Two jewelry certification companies were found to have forged other institutions' credentials and authorized signatures on certificates they issued, resulting in confiscated proceeds and fines.
What Is NGTC? China's Only National-Level Gem Testing Authority
NGTC — the National Gemstone Testing Center — is currently administered under the Gem and Jewelry Administrative Center of China's Ministry of Natural Resources. Its origins trace back to a gemstone monitoring unit under the former Ministry of Geology and Mineral Resources in the early 1990s. In 1995, the center was formally approved and named the National Gemstone Testing Center by China's then State Bureau of Technical Supervision. Following successive rounds of institutional reform, it was eventually restructured into a wholly state-owned enterprise, the National Gemstone Testing Group Co., Ltd. — the entity commonly referred to today as NGTC, or "Zhubao Guojian" in the trade.
National-Level Authorization
Authorized by China's State Administration for Market Regulation as a national-level gemstone quality inspection body, holding metrology and laboratory accreditation.
National Standard-Drafting Authority
Home to the secretariat of the National Technical Committee for Standardization of Gems and Jewelry (SAC/TC298), helping draft China's national standards (GB/T) for diamond grading, jade grading, and more.
Multi-City Laboratory Network
Operates laboratories in Beijing, Shanghai, Shenzhen, Guangzhou, Yunnan, Pingzhou, Shenyang, Zhuji, Hong Kong, and Mumbai.
Officially Designated Functions
Designated as a national scientific and technological achievement appraisal body, an import/export commodity inspection laboratory, and the China Consumers Association's official testing partner.
NGTC's role in drafting national standards, combined with ongoing government oversight, is why it's generally regarded as comparatively credible and well-resourced within China's domestic jewelry industry — though that doesn't mean it is flawless. Whatever institution issues a certificate, buyers should still independently verify it through an official channel.
NGTC's Testing Services: Diamonds, Jade, and Colored Gemstones
NGTC's testing scope covers more than a hundred varieties of natural and man-made gems, including:
Diamond 4C Grading
Color, clarity, cut, and carat weight grading for loose and mounted diamonds.
GB/T 16554, Diamond GradingLab-Grown Diamond Quality Evaluation
Quality evaluation for colorless-to-near-colorless and fancy-color lab-grown diamonds, kept separate from natural diamond grading reports.
Enterprise Standard Q/NGTC-J-SZ-0001Fancy Yellow Diamond Grading
Hue, saturation, tone, and clarity grading for loose and mounted fancy yellow diamonds.
GB/T 34543, Yellow Diamond GradingJadeite Grading
Color, texture, and workmanship grading for rough and finished jadeite.
GB/T 23885, Jadeite GradingRuby / Sapphire / Emerald Grading
Grading covering color, clarity, brilliance, cut, and heat-treatment category.
GB/T 32863, GB/T 32862, GB/T 34545Pearl Grading
Grading for saltwater and freshwater pearls across color, size, luster, and nacre thickness.
GB/T 18781, Pearl GradingPrecious Metal Purity Testing
Purity testing for gold, silver, platinum, and palladium, applicable to karat gold and platinum jewelry.
GB 11887, GB/T 18043Gemstone Origin Testing
Specialist origin-determination service for ruby, sapphire, emerald, and amber.
For a closer look at how the international IGI certification system works, see our Ultimate Lab-Grown Diamond Certification Guide.
Finished Jewelry Testing: Why the Diamond and the Metal Setting Are Graded Separately
Many buyers assume a mounted ring or pendant needs just one certificate. In practice, NGTC — like most reputable testing bodies — treats the stone and the metal setting as two separate testing items, each assessed against a different standard:
Diamond 4C & Quality Evaluation
Graded under GB/T 16554 for color, clarity, cut, and weight. Lab-grown diamonds are evaluated separately under enterprise standard Q/NGTC-J-SZ-0001, with a different report format.
Precious Metal Purity Testing
Typically measured by X-ray fluorescence spectroscopy, and reported as 9K, 18K, 24K, Pt950/Pt990 platinum, or 925 sterling silver, depending on the piece.
9K Gold
Approximately 37.5% gold content. Harder and more scratch-resistant, well suited to everyday-wear settings.
18K Gold
Approximately 75% gold content. Richer color and better malleability — the most common specification for diamond rings and pendants.
24K Gold / Platinum
24K gold runs approximately 99.9% purity and is softer, typically used for plain-gold pieces. Platinum is graded separately, most often as Pt950 or Pt990.
Buyer's tip: When buying a finished, mounted piece, check that the diamond report's identifying details (particularly a laser inscription number, where present) and the metal setting's purity marking are both clearly stated and consistent. Either one on its own isn't enough to confirm the piece's overall quality. Every MadisonDia finished piece lists the center stone and the 9K/18K gold setting as separate, clearly stated specifications so you can check both.
NGTC Hong Kong vs. Mainland China Labs: MadisonDia's Recommendation
Many buyers assume NGTC only operates in mainland China. In fact, NGTC also runs a branch laboratory in Hong Kong. Compared with its major mainland labs in Beijing, Shanghai, Shenzhen, and Guangzhou, however, the Hong Kong branch is a considerably smaller operation.
MadisonDia's recommendation: If you're based in mainland China and want a diamond or piece of jewelry additionally certified by NGTC, we recommend using one of NGTC's major mainland laboratories (Beijing, Shenzhen, or Shanghai) rather than the Hong Kong branch, given the difference in scale and testing volume. If you're based in Hong Kong, every MadisonDia center stone of 1ct or above already comes with an IGI report — the leading international standard for lab-grown diamond grading — so a further NGTC check through the Hong Kong branch is generally unnecessary.
MadisonDia's Certification Standard, and the Optional NGTC Add-On Service
Every MadisonDia center stone of 1ct or above is graded to D color, VVS clarity, and Triple Excellent cut as a baseline, and comes with an IGI report. Accent stones under 1ct — for example, the melee in a pavé eternity band — are held to D–E–F color and VS–VVS clarity, graded internally against our MISI™ standard, without an IGI report or a Triple Excellent claim. IGI is the leading international standard for lab-grown diamond grading, covering the large majority of lab-grown diamond reports worldwide.
That said, we understand some clients based in mainland China also want a diamond backed by an NGTC-recognized certificate — for resale, gifting, or their own peace of mind.
MadisonDia can arrange NGTC certification on request, at an additional cost. Email us for pricing and details.
Email us: info@madisondia.comHow to Verify an NGTC Certificate Before You Buy
Finished jewelry carries a real risk of certificate swapping. For mounted pieces, NGTC certificates rely primarily on a photograph and a written weight description to match the certificate to the item — not on a permanent marking on the stone or metal itself. This differs from how some international reports handle loose diamonds, where a laser-inscribed number on the girdle can be checked under magnification against the certificate to confirm it's the same physical stone. A mounted piece typically has no equivalent permanent link between the certificate and the item.
Because there's no tamper-evident connection between certificate and item, "certificate swapping" is a real risk in practice — a genuine certificate belonging to one piece can be paired with a different, similar-looking (and often lower-quality) piece, and it's very difficult to catch from the certificate alone.
What to do: Before paying, check the certificate's photo, stated weight, and physical characteristics against the actual item in hand, and independently verify the certificate number through NGTC's official channel. Where possible, favor loose center stones with laser inscription, which reduces the risk of the certificate becoming separated from the stone.
Beyond that specific risk, a few habits are worth building into every purchase:
Use an Official Verification Channel
Verify the certificate number directly through the issuing lab's own official system rather than trusting a photo of the certificate supplied by the seller.
Check for Accreditation Marks
Certificates from legitimate labs typically carry a statutory accreditation mark such as CMA. A certificate with none of these marks is worth treating with suspicion.
Be Wary of "No Sample Required"
Legitimate labs require the physical item to be submitted for inspection. If a seller offers a certificate from a photo alone, for a few dollars, that's a red flag.
Match Weight and Appearance
Certificates include a photo and precise weight of the item at the time of testing — compare both against the shape, color, and specifications of the piece in hand.
Vet the Seller's Background
Before you buy, look into the seller's company background, whether they hold the relevant licenses, and whether they source authentic goods — and note whether they have credible KOL or third-party endorsements as an added signal of reliability.
For a closer look at choosing the right stone by the 4Cs, see our How to Choose a Lab-Grown Diamond guide, or start with What Is a Lab-Grown Diamond if you're new to the topic.
Frequently Asked Questions
What is NGTC?
NGTC, the National Gemstone Testing Center, is a national-level gemstone inspection body authorized by China's State Administration for Market Regulation. It is currently administered by the Gem and Jewelry Administrative Center under the Ministry of Natural Resources, and operates as the state-owned National Gemstone Testing Group Co., Ltd.
How does NGTC differ from other mainland Chinese testing bodies?
NGTC carries national-level authorization, hosts the secretariat for China's national gem and jewelry standards committee, and operates laboratories across Beijing, Shanghai, Shenzhen, and other major cities under ongoing government oversight — which is why it's generally regarded as one of the more credible options in mainland China.
Can NGTC test lab-grown diamonds?
Yes. NGTC uses a dedicated enterprise standard, Q/NGTC-J-SZ-0001, to evaluate colorless-to-near-colorless and fancy-color lab-grown diamonds, keeping this separate from its natural diamond grading reports so buyers can clearly identify a stone's origin.
Do all MadisonDia diamonds come with an NGTC certificate?
MadisonDia's baseline standard for every center stone of 1ct or above is an IGI report, the leading international standard. NGTC certification is available as an optional paid add-on — email info@madisondia.com for pricing and details.
Why isn't NGTC's Hong Kong branch MadisonDia's first choice?
NGTC does operate a Hong Kong branch, but it is considerably smaller than the major mainland laboratories in Beijing, Shanghai, Shenzhen, and Guangzhou. For clients based in mainland China who need NGTC certification, MadisonDia recommends a major mainland lab instead, given the difference in scale and credibility.
How do I verify an NGTC certificate is genuine?
Verify the certificate number through NGTC's own official verification channel, check for statutory accreditation marks such as CMA, and compare the certificate's photo and stated weight against the physical item.
Which diamonds come with an IGI certificate?
IGI certification applies to MadisonDia center stones of 1ct or above, graded to D color, VVS clarity, and Triple Excellent cut. Accent stones under 1ct — such as pavé melee — are graded to D–E–F color and VS–VVS clarity against our internal MISI™ standard, without an IGI report or a Triple Excellent claim.
Why are some mainland Chinese testing certificates unreliable?
The barrier to entry for gem testing businesses in China is relatively low, and some operators skip standard submission and verification steps entirely, occasionally issuing certificates without physically inspecting the item. State media has reported repeatedly on forged certificates and misuse of other labs' credentials, so buyers should independently verify a certificate's source before relying on it.
References: National Gemstone Testing Group Co., Ltd. — Testing Services, Ministry of Natural Resources of the People's Republic of China, China News Service — report on jewelry certificate fraud.
