corundum, treatments.6, gems

Describes observations of ruby heat-treatment preparations near Chanthaburi, Thailand, during a Gemmological Association of New Zealand tour in September 1987, and investigates the possible composition and function of a proprietary liquid added to the stones. Independent Thai operators are described as specialising in particular oxidation or reduction treatments, using individual methods and closely guarded procedures; consequently, a stone may pass through several treatment attempts before improvement or rejection. In the demonstration, a fresh crucible was fashioned from blended local clays, charged with a small quantity of clear liquid and seven uncut rubies weighing approximately 4–6 carats each, sealed with clay, wrapped in damp newspaper and surrounded by charcoal in a firebrick-lined oil-drum kiln. The operator demonstrated the liquid separately by placing a cupro-nickel coin in it. After an initial delay, the solution developed a green-blue colour and released increasing amounts of brown gas identified as nitrogen peroxide, leaving the coin bright after washing. The liquid was colourless, mobile and reportedly contained only three ingredients. From these observations and additional informal evidence of its moderate acidity, Currie inferred that its principal components were nitric acid and water, with a third ingredient that enhanced its action on the alloy. Hydrochloric acid was considered but judged inconsistent with the solution’s apparent stability and lack of yellowing or fuming. Common salt was proposed as a more plausible additive. Subsequent experiments in New Zealand produced a nitric-acid, water and sodium-chloride mixture whose appearance, stability, acidity and action on cupro-nickel resembled those observed in Thailand. The author suggests that nitric acid could provide oxidising conditions intended to convert ferrous to ferric iron. Possible benefits of chloride are explored by analogy with the volatilisation of base-metal chlorides during gold refining and the use of chlorides in pyrotechnics. These explanations remain speculative: the original liquid was not chemically identified, its effectiveness on the demonstrated rubies was not observed, and the proposed mixture was not tested in ruby heat treatment because suitable untreated rough was unavailable. The account therefore offers a tentative interpretation of treatment preparations rather than a verified formulation or demonstrated enhancement mechanism.