15.48ct Opal and Platinum Ring

This exquisite piece of fine jewelry features a substantial 15.48-carat oval cabochon cut natural opal as its centerpiece. Found within a high-quality platinum mounting, the opal exhibits a soft, milky white-to-translucent base body color with a vibrant 'play-of-color' consisting primarily of green, yellow, and subtle orange pinfire and broadflash flashes. The gemstone is secured by a six-prong setting, ensuring the large stone remains stable. The shank is constructed of polished platinum and features intricate openwork detailing on the shoulders, likely embellished with small accent diamonds typical of mid-to-late 20th-century craftsmanship. Interior markings on the band include a 'PM900' stamp, indicating a high-purity platinum alloy (90% platinum), alongside other discernible maker's marks or serial numbers. The overall condition appears excellent with minimal surface abrasions to the opal and a well-maintained polished finish on the metal. The massive scale of the opal suggests it is a premium collector-grade stone, likely of Australian origin. The ring represents a classic cocktail style, prioritizing the size and spectral brilliance of the central opal.

I have conducted a visual examination of the 15.48ct Opal and Platinum Ring. The central 15.48-carat natural opal serves as the focal point, exhibiting a desirable translucent body with significant green and yellow play-of-color. The PM900 stamp confirms the high-purity platinum mounting, consistent with premium Japanese or international craftsmanship from the mid-20th century. The condition is excellent, showing minimal crazing or surface wear, which is vital for opal longevity. Market demand for large-scale cocktail rings remains steady among collectors. Comparables for Mexican or Australian opals of this size typically range between $200 and $400 per carat for the stone alone, with the platinum mounting adding significant melt and craftsmanship value. The rarity of a 15ct+ stone with consistent fire significantly elevates it above standard commercial jewelry. However, several factors cannot be determined via imagery. A physical inspection is required to check for 'crazing' (internal cracking due to dehydration) and to confirm if the stone is a natural solid opal, a doublet, or a triplet. Furthermore, the presence of enhancement—such as smoke treatment or sugar-acid treatment—must be ruled out via a gemological laboratory (e.g., GIA or SSEF). While the PM900 mark is a strong indicator of authenticity, X-ray fluorescence (XRF) testing would confirm the alloy's exact composition. Valuation is based on the assumption of a natural, untreated solid opal of Australian origin.