Labs & certification

The Gemological Institute of America (GIA), established in 1931 by Robert M. Shipley, is a nonprofit that created the diamond scales most of the trade uses. Its own timeline names laboratories in New York, Tokyo, Johannesburg, Mumbai, Gaborone, Ramat Gan, Surat, Antwerp and, in 2024, Dubai. The International Gemological Institute (IGI) was founded in Antwerp in 1975 and now reports 31 laboratories and 18 schools. Blackstone bought IGI in May 2023. On January 31, 2026 IGI announced the acquisition of New York's American Gemological Laboratories (AGL), which AGL confirmed on February 2. AGL keeps its name, its New York laboratory and its president, Christopher Smith, and says its methods are unchanged, but it belongs to IGI: the two are one group, not two independent opinions. AGL's own site calls it America's first origin laboratory. HRD Antwerp descends from the Hoge Raad voor Diamant, split in 2007 from the Antwerp World Diamond Centre. AGS Laboratories, formed in 1996, was a diamond grading laboratory; it closed in 2022, and its AGS Ideal report is now issued by GIA.

For colored stones a few laboratories set the reference at auction: SSEF in Basel, the Gübelin Gem Lab in Lucerne, GRS at Meggen, Lotus Gemology in Bangkok and the Central Gem Laboratory in Tokyo. Ownership varies: the Gem and Jewelry Institute of Thailand (GIT) is a Thai state body, and DANAT in Manama belongs to Bahrain's sovereign wealth fund Mumtalakat.

A laboratory report describes a stone. Depending on the service it records species or variety, measurements, weight, grades where a scale exists, detectable treatments and, for some colored stones, an opinion on geographic origin. It does not state a price. GIA says plainly that it does not certify or appraise anything submitted to it. The Laboratory Manual Harmonisation Committee (LMHC), formed in 2001 and made up of CGL, CISGEM, DSEF, GIA, GIT, the Gübelin Gem Lab and SSEF, recommends wording stating that all findings are the laboratory's opinions given to the best of current knowledge, that some heating and irradiation processes are not currently detectable, and that in no case does a report reflect the value of a gemstone. The CIBJO Gemmological Laboratories Book separates a report from a certificate, which it defines as a document of legal standing.

An appraisal is a valuation written for a stated purpose, and the purpose drives the number. Insurance appraisals usually give replacement value. Estate, tax and settlement work uses fair market value, which the United States Internal Revenue Service defines as the price a willing buyer and a willing seller would agree on, neither compelled to act and both reasonably informed. The IRS adds that an insured replacement value is not fair market value, and that gems and jewelry are specialized enough to need a specialist appraiser.

Color and clarity grades are judgments made against reference stones, so a diamond close to a boundary can receive different grades from different laboratories, or from the same laboratory on resubmission. Michael Cowing, testing blue-fluorescent diamonds for The Journal of Gemmology in 2010, found GIA and the American Gem Society Laboratory grading the same stones as much as two grades apart, and priced that gap at 2010 rates. Because adjacent grades carry different prices, sellers have an incentive to submit a stone to several laboratories and keep the best result, a practice called lab shopping, and laboratories competing for that business face pressure toward soft grading.

GIA's worst episode is known only from trade press, which this chapter otherwise excludes, so it is given here as those reports give it. JCK reported that in April 2005 the dealer Max Pincione sued Vivid Collection, two individuals and GIA, alleging that payments had been made to have diamonds upgraded. GIA denied the allegations and opened an internal investigation. Rapaport reported that GIA's statement of October 18, 2005 gave four laboratory employees dismissed and the laboratory head replaced. No court record and no surviving GIA statement were reachable.

Laboratory-grown diamonds created a different problem. In June 2025 GIA said more than 95% of them fall into a narrow range of color and clarity, and from October 1, 2025 it stopped applying the natural scales to them, describing them as premium or standard.

An origin report gives a laboratory's opinion on where a stone was most likely mined. GIA offers it for ruby, sapphire, emerald, Paraíba tourmaline, red spinel and alexandrite, and says it cannot reach a determination in every case. The evidence comes from three directions. Inclusions, the crystals, fluids and growth features trapped inside, reflect the rock the stone grew in. Trace-element chemistry, measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), gives a chemical signature. Spectroscopy adds absorption and luminescence data. Each result is compared with reference collections gathered as close to the mine as possible.

The limits are hard. GIA's 2019 studies report significant overlap between deposits formed in the same geological event, notably marble-hosted rubies from Burma, Vietnam, Tajikistan and Mong Hsu, and partial overlap between basalt-related and metamorphic sapphires. Heating that deepens blue color destroys the rutile silk the method depends on. When the data are ambiguous, laboratories issue an inconclusive opinion, and GIA expects laboratories to differ on the harder calls, blue sapphire above all.

Physical tracing tries to replace inference with a record. The Gübelin Gem Lab's Emerald Paternity Test places DNA-based nanoparticles encoded with the mine's information inside the stone at the source, so it covers only material tagged where it was mined.