jade, jadeite, fei cui, assembled stones, treatments, Burma, gems

Two examples of coated fei cui illustrate a treatment in which surface varnish improves colour and appearance while producing gemmological properties that can obscure the identity and treatment of the underlying material. During a visit to Taiwan, an editor examined a 117.99 ct bead, approximately 24 mm in diameter, supplied by Ten S.-T. Wu and Peter Chiu. The bead consisted of greyish purple fei cui covered with mottled green varnish and, viewed from a distance, convincingly resembled fine-quality material. Closer examination revealed that part of the coating had spalled away, exposing the original colour. Its refractive index of 1.52 was too low for fei cui and was attributed to the coating, while its specific gravity of 3.29 was slightly below the usual value. Strong chalky blue fluorescence under long-wave ultraviolet radiation, with a weaker short-wave reaction, was also considered to originate primarily from the varnish; natural fei cui fluorescence was described as generally spotty and yellowish white. Contact with a hot point melted the coating. A similarly treated pipe, approximately 8 cm long, was coated externally but not internally. Refractive-index readings of 1.54 on coated areas and 1.66 on exposed material distinguished the surface layer from the substrate. A moderate absorption line at 437 nm supported identification of the underlying material, which was further confirmed by energy-dispersive X-ray fluorescence comparison with documented reference samples. Reflected-light microscopy of chipped areas revealed two distinct coatings: an inner mottled green layer apparently intended to enhance colour and an outer colourless or very pale yellow layer interpreted as a protective varnish. Both fluoresced yellow-green under ultraviolet radiation, with differing intensities, whereas the substrate was inert. Infrared spectroscopy showed strong absorption around 2900 cm⁻¹, consistent with an organic coating. Because comparable absorption can occur in bleached and polymer-impregnated B-type fei cui, the authors emphasise that infrared evidence alone could lead to an erroneous diagnosis of impregnation. Microscopic examination of the surface, supported by optical, spectroscopic and chemical observations, established coating as the treatment present.