A Chatham ruby is a flux-grown synthetic ruby produced by Chatham Created Gems, the San Francisco–based laboratory founded by Carroll Chatham in the 1930s. Like all synthetic gemstones in the gemmological sense, Chatham rubies share the essential chemical composition, crystal structure, and optical properties of their natural counterparts — aluminium oxide (Al₂O₃) of the corundum species, coloured red by chromium — while originating entirely in a controlled laboratory environment. They are distinguished from natural ruby and from other synthetic rubies by a suite of characteristic inclusions and growth features that reflect the flux-melt process by which they are created. First offered commercially in the mid-twentieth century, Chatham rubies occupy a well-defined niche in the jewellery market: they are sold with full disclosure as laboratory-created stones and appeal to buyers seeking the optical beauty of ruby with greater cost accessibility and a traceable, conflict-free origin.

The Flux-Growth Process

Chatham's rubies are produced by the flux method, a high-temperature dissolution technique in which aluminium oxide and chromium oxide are dissolved in a molten flux — a chemical solvent, typically comprising lead fluoride or a related compound — held in a platinum or ceramic crucible at temperatures in the range of 1,000–1,400 °C. As the melt cools very slowly, corundum crystallises out of solution over a period of months to years. The extended growth cycle is central to Chatham's identity: the company has historically emphasised that its crystals are grown over timescales measured in months rather than days, yielding material with relatively low internal strain and a clarity profile that can approach gem quality without the mechanical stresses associated with faster synthesis methods such as the Verneuil flame-fusion process.

The flux method was the same broad technique Chatham applied to its pioneering synthetic emeralds, for which the company became internationally known from the 1960s onward. Applying it to corundum presented different technical challenges — corundum's melting point is considerably higher than that of beryl — but the fundamental crystal-growth chemistry is analogous.

Gemmological Properties

Because Chatham rubies are chemically and structurally identical to natural corundum, their measurable physical and optical constants fall within the natural ruby range:

• Chemical composition: Al₂O₃ with Cr³⁺ as the primary chromophore
• Crystal system: Trigonal
• Refractive indices: approximately 1.762–1.770 (birefringence 0.008–0.009), consistent with natural corundum
• Specific gravity: approximately 3.99–4.01
• Hardness: 9 on the Mohs scale
• Fluorescence: strong red under long-wave ultraviolet, consistent with chromium-bearing corundum

Standard gemmological instruments — refractometer, polariscope, spectroscope — will not distinguish a Chatham ruby from a natural stone. Identification depends on microscopic examination and, in some cases, advanced spectroscopic analysis.

Diagnostic Inclusions and Identification

The flux-growth environment leaves a characteristic fingerprint that trained gemmologists and laboratory gemologists can identify under magnification. The principal diagnostic features of Chatham and other flux-grown synthetic rubies include:

• Flux inclusions: Wispy, veil-like clouds of residual flux material, often appearing as irregular, translucent to opaque masses with a glassy or resinous lustre. These are the most immediately recognisable feature and have no analogue in natural ruby inclusions.
• Platinum platelets: Minute, highly reflective metallic platelets of platinum, shed from the crucible walls during growth. Under reflected light these appear as bright, mirror-like flakes and are essentially diagnostic of flux-grown material produced in platinum vessels.
• Curved or angular growth zoning: Colour and transparency zoning that follows the geometry of the growing crystal faces, sometimes appearing as angular banding when viewed under crossed polars or with the Chelsea filter.
• Absence of natural inclusions: Natural rubies commonly contain rutile silk, calcite, spinel, or other mineral inclusions characteristic of their geological host. The absence of such inclusions, combined with the presence of flux features, strongly supports a synthetic origin.

Major gemmological laboratories — including the GIA, Gübelin Gem Lab, and SSEF — routinely identify flux-grown synthetic rubies and will note the synthetic origin on any report issued. The GIA's research publications have documented the inclusion suites of flux-grown corundum in detail, providing a well-established reference framework for identification.

Colour and Appearance

Chatham rubies are produced in a range of red hues, from lighter pinkish-red to deeper, more saturated tones. The chromium content can be adjusted during growth to influence colour saturation. At their best, flux-grown rubies from Chatham can display a vivid, pure red with good transparency, and the material is generally free of the fractures and heavy inclusions that affect a significant proportion of natural ruby rough. This freedom from fracture is commercially significant: natural rubies are almost universally fracture-filled or otherwise treated, whereas Chatham rubies require no post-growth clarity enhancement.

The colour of flux-grown synthetic ruby is sometimes described as slightly more uniform than that of fine natural material, lacking the subtle zoning and depth that connoisseurs associate with stones of Burmese or Mozambican origin. This is a matter of aesthetic preference rather than objective quality, but it is a distinction that experienced buyers and collectors note.

Market Position and Disclosure

Chatham Created Gems has consistently marketed its products with explicit disclosure of their synthetic origin, a practice that distinguishes it from fraudulent misrepresentation and aligns it with the disclosure standards mandated by the US Federal Trade Commission and the trade guidelines of bodies such as the American Gem Trade Association (AGTA). The AGTA's nomenclature guidelines require that laboratory-created gemstones be described as such, and Chatham's marketing has historically been constructed around, rather than in spite of, the laboratory origin of its stones.

In the trade, Chatham rubies are priced substantially below natural rubies of comparable apparent quality. A fine natural Burmese ruby of even modest size commands prices that can reach tens of thousands of dollars per carat, driven by rarity, provenance, and the prestige of the natural origin. Chatham rubies, by contrast, are priced as manufactured goods, reflecting the cost of materials, energy, and production time rather than geological scarcity. This price differential makes them accessible for use in jewellery at price points where natural ruby of equivalent visual quality would be unattainable.

The ethical sourcing argument has gained traction with consumers concerned about the provenance of natural rubies, a significant proportion of which have historically originated from Myanmar (Burma) under conditions that raised human rights and sanctions concerns. Laboratory-created rubies offer a fully traceable alternative, though the natural ruby trade has also evolved, with Mozambican production now supplying a substantial share of the market through more transparent supply chains.

Chatham in Context: Other Flux-Grown Rubies

Chatham is not the only producer of flux-grown synthetic ruby. Other historically significant manufacturers have included Knischka (Austria), Ramaura, and Kashan, each of which produced flux-grown corundum with subtly different inclusion characteristics that allow laboratory identification of the specific manufacturer in many cases. Gübelin and SSEF have published reference data enabling such differentiation. The Verneuil (flame-fusion) process produces a far less expensive synthetic ruby with curved striae and gas bubbles rather than flux inclusions, and is considered a lower-quality product for jewellery purposes. Hydrothermal synthetic rubies, grown from aqueous solution under pressure, represent a third manufacturing route. Among flux-grown producers, Chatham occupies a position of particular historical significance as one of the earliest and most commercially prominent names in the laboratory-gemstone industry.

Further Reading

• GIA Gems & Gemology — Synthetic Ruby Identification
• GIA Gem Encyclopedia: Ruby
• AGTA Gemstone Information