N (No Treatment) — The AGTA Code for Unenhanced Stones
N (No Treatment) — The AGTA Code for Unenhanced Stones
The disclosure designation indicating no detectable enhancement under current laboratory methods
N is the AGTA gemstone enhancement code indicating that no treatment or enhancement has been detected in a stone using current laboratory methods. The designation appears on AGTA-aligned laboratory reports, dealer invoices, and trade documents to signal that the stone is in its natural state as recovered, with no heat, irradiation, fracture-filling, diffusion, or other modification detectable by the testing applied.
The AGTA code system
The American Gem Trade Association maintains a standardised set of single-letter and short-form codes for gemstone enhancements: N (none), H (heat), F (fracture-filling), C (coating), I (impregnation), B (bleaching), D (dyeing), R (irradiation), U (diffusion), and others. The codes are part of the AGTA Code of Ethics and Information Disclosure, used widely in the North American coloured-stone trade and aligned with CIBJO and FTC disclosure expectations. Each species and treatment combination has expected codes — ruby that reads N, for instance, is a meaningfully different commercial proposition from ruby that reads H or HR.
Limits of the designation
'No treatment detected' depends on what the laboratory tested for and the sensitivity of the methods used. Treatments that operate below modern detection limits — undocumented thermal events, very faint diffusion treatments, certain new processes not yet in the analytical literature — may pass as N even though some intervention has occurred. The major laboratories — GIA, Gübelin, SSEF, Lotus, AGL — publish their analytical protocols and update them as new treatments emerge, but no laboratory claims absolute certainty. The N code reflects current best-effort detection.
Premium
Stones graded N command sharp premiums in species where treatment is standard or near-universal. Unheated ruby, sapphire, and tanzanite, unenhanced emerald (no oil), and untreated padparadscha sapphire all trade at multiples over their treated counterparts of similar appearance. The premium is most pronounced at the high end of the size and quality range, where the supply of N-grade material is thinnest and demand is concentrated.