As printed in Canadian Jeweller, November 2004 issue, p. 82
By Ronald R. Dupuis, FGA, GJ

Estate jewellery as a source of rare and fine gems

Most of us have heard the expression “hidden gem.” In the case of estate jewellery, the phrase is more than just a metaphor. Estate jewellery can turn up anywhere – it’s often sold in the same shops as newly made pieces, where it is often overlooked, yet turns up frequently at auction, where it can sell for premium prices. True collectors scour both venues. But what are they looking for, and what makes a great piece of estate jewellery worth the search? Often, it has to do with the gemstones. This column looks at four in particular: demantoid garnets, alexandrite, Kashmir sapphires and natural pearls, in order to help you identify, appraise and appreciate these extraordinary creations.
Demantoid garnets were mined in the Ural Mountains from the mid-19th century to the beginning of the Russian Revolution in 1917. Mining has recently been renewed, but the results are poor, making pre-1917 demantoid garnets the rarest and most costly of the garnet family. Though similar in hue to the peridot, being a yellowish green, the remarkable brilliance of the gem is on par with diamonds. For this reason, perhaps, they were favorites of the Victorian and Edwardian master jewellers. Karl Fabergé used demantoids profusely in both his jewellery and his decorative objects. They were the delight of King Edward VII, and many Edwardian pieces reflect this in settings that contrast the clear green of the demantoids with the white flash of diamonds and cold lustre of platinum.
Demantoids are the softest of all garnets, at 6.5 on the Mohs scale, and the shape of their crystal structure usually prevents them from being cut into stones larger than two carats. The presence of so-called ‘horsetail’ inclusions exacerbates the problem. These needle-like fissures are exclusive to these stones, and are often highlighted by cutters, actually increasing the gem’s value. Stones over five carats have been known to fetch more than US$10,000 per carat and are seldom seen outside museum collections.
Almost as rare are Kashmir sapphires, which were mined intensively over a 40-year period at the end of the 19th century from mines in the Himalayan mountains of the former Indian state. While early mining was limited to certain months of the year because of the wild climate, mining is currently impossible due to fighting in the region. Kashmir sapphires, the most valuable of all, differ markedly from later examples and from sapphires of other regions. Their most obvious identifying characteristic is the velvety blue color and medium to medium-dark tone. They are often referred to as cornflower blue. The color is often distributed in zones, and loses none of its intensity when viewed under artificial light, in contrast to many lesser sapphires. There is often a slight cloudy haziness to the stone, created by the diffusion of light over thousands of tiny, liquid-filled raspberry red by artificial light. Early stones show this characteristic, where later examples, still mined in Sri Lanka, East Africa and Brazil, lack the intensity of color and color change. The early gems were especially high quality and highly prized.
Far more ancient, if only in usage, are natural pearls. These are formed by certain saltwater and freshwater molluscs in which an irritant or parasite causes the animal to deposit dense, concentric layers of nacre around the offending article in an effort to soften the irritation; the larger the pearl, the longer it has existed within its host. It can take many more years to produce a natural pearl than a cultured pearl.
While natural pearls adorn the sitters in many ancient and aristocratic portraits, they virtually disappeared from the mainstream jewellery market in the 20th century, and the few that turn up from the dives still made are poor examples, procured at enormous cost. Pollution and over-fishing have resulted in the endangerment of many of the molluscs that would naturally produce these gems. The result is that fine examples are only available through antique and estate jewellers and auctions, where they always command very high prices. Natural pearls bear a number of characteristics that prevent their being mistaken for their poorer cousins, cultured pearls. Of these, their individuality is foremost; no two in a strand are exactly alike. They will differ in shape, especially, because few are truly round, but more ovoid in shape. They are usually creamier in color than cultured pearls, and have a lustre and  soft-iridescence that sets them apart. Use a loupe to study the interior of the drill hole: there should be no visible demarcation where the layer of conchiolin lies atop the original mother-of-pearl bead, which identifies a culured pearl. When in doubt, consult with a lab that can produce an X-ray analysis.
Greater understanding of the gems contained in antique jewellery will enhance not only your own appreciation, but that of your clients, and will assist you in offering the most concise appraisals for the most logical reasons. And from there, the thrill of ownership can’t be far behind!

Equally unusual is alexandrite, named for the young Tsar Alexander, on whose birthday the first stone was found in the Ural Mountains. That was in 1830, and by the early 1900s the source had been depleted. These are the rarest and most expensive form of chrysoberyl. They are remarkable for their changeable nature: emerald green body by daylight and distinctive, internal fissures, although these are often difficult to distinguish, even under the microscope. Once seen, they are never forgotten and never mistaken for lesser sapphires.