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Cam Hatch
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This article is in the latest GIA newsletter.
From Gems & Gemology: Imitation Melo "Pearls"
This sphere and ovoid (158.69 and 142.43 ct, respectively) were submitted for identification as possible Melo ?pearls.? They proved to be dyed shell, as evidenced by the prominent banded structure.
Recently, GIA?s West Coast laboratory received two unusual spherical objects for identification. The client had purchased them in Vietnam as rare, nonnacreous Melo ?pearls,? which are produced by the Melo genus of mollusk and are notable for their orange color and interesting flame structure. Although these items had some visual similarities to Melo ?pearls,? they proved to be a very different product.
The first item was a translucent, banded, orange-to-white sphere that measured 27.75?28.05 ? 27.15 mm. The second was a translucent, banded, light orange-yellow to orange ovoid that measured 27.40?27.65 ? 24.65 mm. Both had a prominent banded structure. The sphere had a coarse flame structure oriented perpendicular to the banding, but it was difficult to distinguish any flame structure on the ovoid. Although no dye was removed by swabbing with acetone, low-power magnification revealed numerous fractures and some cavities, both with orange dye concentrations. There were also wheel and polishing marks on the surfaces of the samples, which indicated that they had been fashioned. Fluorescence was moderate to long-wave UV radiation and weak to short-wave UV, and was a combination of chalky orange and yellow; the uneven fluorescence patterns appeared banded, with either spots or swirls.
Spot R.I.?s gave a birefringence blink for both samples, with values of 1.50?1.67 for the sphere and 1.52?1.67 for the ovoid. The S.G. values were 2.84 and 2.86, respectively. No absorption bands were visible in the desk-model spectroscope.
Coincidentally, the GIA Laboratory had recently completed the identification of a true Melo ?pearl? submitted by Evan Caplan of Omi Gems, Los Angeles. Although some of the properties (such as R.I.) overlapped with the two other samples, there were distinct differences. When examined with magnification, the 26.60 ? 25.60 ? 25.50 mm (129.81 ct) Melo ?pearl? also presented a very coarse flame structure, but the surface was slightly dimpled, especially at the bases of these flame structures, and there was no banding. It had a porcelaneous luster that is also characteristic of conch ?pearls.? (The same high luster was not seen in the samples in the figure.) Its UV fluorescence was distinctly different from that of the other two samples as well. When exposed to long-wave UV radiation, the Melo ?pearl? fluoresced a very weak brown that was mottled with weak-to-strong chalky greenish yellow spots; it was generally inert to short-wave UV, but also showed weak chalky greenish yellow spots.
Given the differences between the two samples and natural Melo ?pearls? with regard to structure, the presence of dye, the UV fluorescence, and evidence of fashioning, it was obvious that the two samples were dyed imitations; the R.I. and banded structure indicated shell material. Ken Scarratt, of GIA Research in Bangkok, reports that he has seen a number of such imitations and that they are being produced in Vietnam and Myanmar. Some are fashioned from actual Melo shells (i.e., those that are particularly thick in the whorl), whereas others are manufactured from the shell of Tridacna gigas (the giant clam), which is also being used as a source of bead nuclei. However, it must be reiterated that Tridacna is protected by a CITES agreement, and its importation is restricted.
This report was prepared by Cheryl Y. Wentzell of the GIA Laboratory in Carlsbad, Calif.
From Gems & Gemology: Imitation Melo "Pearls"
This sphere and ovoid (158.69 and 142.43 ct, respectively) were submitted for identification as possible Melo ?pearls.? They proved to be dyed shell, as evidenced by the prominent banded structure.
Recently, GIA?s West Coast laboratory received two unusual spherical objects for identification. The client had purchased them in Vietnam as rare, nonnacreous Melo ?pearls,? which are produced by the Melo genus of mollusk and are notable for their orange color and interesting flame structure. Although these items had some visual similarities to Melo ?pearls,? they proved to be a very different product.
The first item was a translucent, banded, orange-to-white sphere that measured 27.75?28.05 ? 27.15 mm. The second was a translucent, banded, light orange-yellow to orange ovoid that measured 27.40?27.65 ? 24.65 mm. Both had a prominent banded structure. The sphere had a coarse flame structure oriented perpendicular to the banding, but it was difficult to distinguish any flame structure on the ovoid. Although no dye was removed by swabbing with acetone, low-power magnification revealed numerous fractures and some cavities, both with orange dye concentrations. There were also wheel and polishing marks on the surfaces of the samples, which indicated that they had been fashioned. Fluorescence was moderate to long-wave UV radiation and weak to short-wave UV, and was a combination of chalky orange and yellow; the uneven fluorescence patterns appeared banded, with either spots or swirls.
Spot R.I.?s gave a birefringence blink for both samples, with values of 1.50?1.67 for the sphere and 1.52?1.67 for the ovoid. The S.G. values were 2.84 and 2.86, respectively. No absorption bands were visible in the desk-model spectroscope.
Coincidentally, the GIA Laboratory had recently completed the identification of a true Melo ?pearl? submitted by Evan Caplan of Omi Gems, Los Angeles. Although some of the properties (such as R.I.) overlapped with the two other samples, there were distinct differences. When examined with magnification, the 26.60 ? 25.60 ? 25.50 mm (129.81 ct) Melo ?pearl? also presented a very coarse flame structure, but the surface was slightly dimpled, especially at the bases of these flame structures, and there was no banding. It had a porcelaneous luster that is also characteristic of conch ?pearls.? (The same high luster was not seen in the samples in the figure.) Its UV fluorescence was distinctly different from that of the other two samples as well. When exposed to long-wave UV radiation, the Melo ?pearl? fluoresced a very weak brown that was mottled with weak-to-strong chalky greenish yellow spots; it was generally inert to short-wave UV, but also showed weak chalky greenish yellow spots.
Given the differences between the two samples and natural Melo ?pearls? with regard to structure, the presence of dye, the UV fluorescence, and evidence of fashioning, it was obvious that the two samples were dyed imitations; the R.I. and banded structure indicated shell material. Ken Scarratt, of GIA Research in Bangkok, reports that he has seen a number of such imitations and that they are being produced in Vietnam and Myanmar. Some are fashioned from actual Melo shells (i.e., those that are particularly thick in the whorl), whereas others are manufactured from the shell of Tridacna gigas (the giant clam), which is also being used as a source of bead nuclei. However, it must be reiterated that Tridacna is protected by a CITES agreement, and its importation is restricted.
This report was prepared by Cheryl Y. Wentzell of the GIA Laboratory in Carlsbad, Calif.
