Kashan ruby is a flux-grown synthetic ruby produced commercially in the United States from approximately 1970 through the early 1980s by Kashan Industries, a private company based in Texas. Kashan rubies are notable in the synthetic-ruby trade for their high quality of internal appearance, with inclusion suites that mimic those of natural ruby closely enough that early production deceived a portion of the trade and required laboratories to develop specific identification protocols. The name "Kashan" refers to the company; it does not refer to the Iranian city of Kashan or to any Iranian production.

Production

Kashan rubies were grown using a flux-melt process in which corundum components were dissolved in a flux of lead and bismuth oxides at high temperature, allowed to crystallise slowly onto seed material as the system cooled. The slow growth produced relatively coarse internal structures with healed fingerprint inclusions, flux droplets and growth-zone features that closely resembled the inclusion patterns of natural Burmese ruby. The colour saturation was good, the lustre high, and the rough yielded faceted stones that under casual inspection passed for natural material.

Identification

Early Kashan production caused real problems in the trade because conventional inclusion-based identification, which relied on the absence of natural inclusion features in older Verneuil-grown synthetic rubies, was less reliable for flux-grown material. Major laboratories including GIA developed identification criteria specific to Kashan and other flux-grown synthetics including:

• Distinctive flux residues, sometimes including identifiable bismuth and lead at the bench through EDXRF.
• Flux-droplet inclusions with characteristic shapes, often paddle-shaped or feather-like, that differ from the silk and crystal inclusions of natural Burmese ruby.
• Curved growth zoning visible under immersion that indicates synthetic origin even when isolated inclusions appear natural-like.
• UV fluorescence patterns that distinguish flux-grown synthetic ruby from natural Burmese material.
• FTIR and Raman spectra showing flux-related features that natural ruby does not produce.

Modern laboratories identify Kashan and related flux-grown synthetics reliably with combined optical and spectroscopic examination. The historical concern about Kashan material in the trade has receded as identification has matured, but vintage stones from the 1970s and 1980s still appear and require correct identification before sale.

Trade and disclosure

Kashan production ended in the early 1980s, but the stones remain in circulation through estate jewellery and through dealers handling vintage synthetic material. Disclosure as synthetic is mandatory under FTC, CIBJO and trade-association rules. The stones should not be sold as "natural ruby" under any circumstances. Where Kashan-origin material is identified, the appropriate description is "flux-grown synthetic ruby (Kashan)" or, more generically, "flux-grown synthetic ruby".

For the working dealer Kashan rubies are a useful case study in the development of the modern synthetic-identification framework. The category demonstrates that high-quality flux-grown material can closely mimic natural inclusion suites, and that conservative gemmological practice requires laboratory verification for any significant transaction in untreated-ruby category. The lesson generalises to subsequent flux-grown synthetic ruby and sapphire production from Chatham, Kashan, Knischka, Lechleitner and others.