An AGL report is a gemological certificate issued by American Gemological Laboratories (AGL), a New York–based laboratory founded in 1977 by Christopher P. Smith. AGL reports document the species and variety identification, geographic origin, and treatment status of coloured gemstones, and are among the most respected credentials a coloured stone can carry in the North American market. The laboratory is particularly well regarded for its work on the three major coloured gemstones — ruby, sapphire, and emerald — and its origin determinations are accepted by major auction houses and dealers internationally.

Scope and Format

A standard AGL report addresses four principal questions: what the stone is, where it came from, whether it has been treated, and to what degree. The certificate states the gemological species and variety (for example, corundum, variety ruby), followed by a country-of-origin determination where the evidence is sufficient to support one. Treatment disclosure is explicit and graded: AGL distinguishes between the presence of a treatment and its estimated degree of significance, using a scale that ranges from "insignificant" to "significant" for heat treatment residues in corundum, and a separate clarity-enhancement scale for emeralds. Photomicrographs of diagnostic inclusions are routinely included, providing a visual record that supports the laboratory's conclusions and aids subsequent identification. Spectroscopic data — including ultraviolet-visible and infrared spectra — are appended when they contribute materially to the determination.

Origin Determination

AGL's origin methodology draws on a combination of gemological microscopy, spectroscopy, and trace-element chemistry. For ruby, the laboratory's ability to distinguish Burmese (Mogok and Mong Hsu) stones from Thai, African, and other sources is considered a core competency. For sapphire, differentiation among Kashmir, Ceylon (Sri Lanka), Burma, and Madagascar material is supported by both inclusion characteristics and chemical fingerprinting. AGL does not issue an origin determination unless the available evidence meets its internal evidentiary threshold; when data are ambiguous or insufficient, the report states that origin could not be determined rather than offering a speculative attribution.

Treatment Disclosure Policy

AGL's approach to treatment disclosure is notably conservative and objective. Unlike certain competing laboratories, AGL does not assign subjective trade-name colour grades such as "pigeon blood" for ruby or "royal blue" for sapphire, a policy that reflects the laboratory's commitment to reproducible, instrument-based conclusions rather than market-facing designations. Heat treatment in corundum is assessed for its degree of alteration to the stone's natural inclusion landscape; the presence of flux residues, fracture healing, or rutile silk dissolution are each noted and weighted. For emeralds, the jardin and fracture network are evaluated, and the degree of clarity enhancement by oil, resin, or polymer is graded on a five-point scale from "none" to "significant." Beryllium diffusion in sapphire and lead-glass filling in ruby are disclosed as major treatments requiring explicit notation.

Report Types

AGL offers several report formats calibrated to the nature of the stone and the needs of the client:

• Prestige Gemological Report: The laboratory's most comprehensive document, covering identification, origin, and treatment with full photomicrographic and spectroscopic appendices. Intended for significant individual stones.
• Gemological Report: A standard certificate covering identification and treatment; origin determination is included when requested and when the evidence supports it.
• Coloured Stone Report: A more concise format suitable for commercial parcels or lower-value individual stones, focusing on species identification and treatment disclosure.
• Mounted Stone Report: Issued for stones examined in their settings, with appropriate caveats regarding the limitations of mounted examination.

Market Standing

In the American coloured-stone trade, an AGL report carries substantial authority, particularly for ruby, sapphire, and emerald offered at auction or through specialist dealers. Major auction houses including Christie's, Sotheby's, and Bonhams routinely reference AGL certifications in their catalogue notes alongside reports from GRS, Gübelin, and SSEF. The laboratory's conservative methodology — its refusal to inflate value through trade-name colour designations and its explicit grading of treatment degree — is regarded by many dealers as a mark of scientific integrity, though buyers seeking the prestige of a "pigeon blood" or "Kashmir" designation from a laboratory that employs such language will need to seek certification elsewhere. AGL reports are particularly prevalent in the estate and antique jewellery market, where the laboratory's long history means that older certificates are frequently encountered alongside stones that have passed through multiple ownerships.

Further Reading

• Gems & Gemology — GIA's peer-reviewed journal, gia.edu
• AGTA Gemstone Treatment Disclosure, agta.org