Christies auction house sold a two strand natural pearl necklace with matching earrings, brooch and ring to a private Asian buyer for $7.096 million. The necklace features 68 of the finest and largest pearls from the seven strand natural pearl necklace that once belonged to The Royal Treasury of the Maharaja of Baroda.
Useful link:
www.christies.com
Friday, April 27, 2007
Sapphire With Yellowish Orange Surface Coating
(via ICA Early Warning Flash, No.46, August 16, 1991) GIA GTL writes:
Description
The stone is a transparent oval mixed cut weighing 0.98 carat and measuring 6.80x4.90x3.36mm. It is medium yellowish orange in color which to the unaided eye appears uniform in distribution.
Gemological properties
Standard gemological testing identify the stone as a natural corundum. It exhibits no distinct absorption features when examined with a desk-model spectroscope and is inert to both long and short wave ultraviolet radiation. Interestingly, it exhibits no pleochroism when viewed through a calcite dichroscope, something that would be expected in a corundum of this hue and depth of color.
Magnification
Diffused transmitted lighting reveals that the stone has been surface coated. Irregularities in the coating—scratches and pits on pavilion facets as well as abrasions on facet junctions---indicate that this is an essentially colorless stone. Examination in surface reflected lighting reveals a predominantly purple iridescence on pavilion facets.
Additional testing
The ultraviolet visible absorption spectrum was found to be similar to that of natural color yellow sapphire with features related to Fe3+. A qualitative chemical analysis performed by EDXRF reveals the presence of iron as the dominating trace element, with small amounts of potassium, calcium, titanium and gallium. Neither ultraviolet visible absorption spectroscopy nor X-ray fluorescence helped to detect or characterize the coating.
Discussion
The microscope features of this stone show it to have been coated, with the coating being responsible for both the apparent body color and superficial iridescence. It is important to note that this is a surface coating and not a diffusion treatment.
‘Aqua Aura’ is the trade name used for a type of coated gem seen for some time now. This consists of such materials as unfashioned rock crystal specimen as well as faceted rock crystal and colorless topaz to which a thin layer of gold has been applied. The treatment produces a greenish blue apparent body color (the transmission color of the gold coating) and superficial iridescence. Treated gems of these type exhibit microscopic features like those described above. It is possible that the corundum described herein has been subjected to a similar coating but of a different substance.
Description
The stone is a transparent oval mixed cut weighing 0.98 carat and measuring 6.80x4.90x3.36mm. It is medium yellowish orange in color which to the unaided eye appears uniform in distribution.
Gemological properties
Standard gemological testing identify the stone as a natural corundum. It exhibits no distinct absorption features when examined with a desk-model spectroscope and is inert to both long and short wave ultraviolet radiation. Interestingly, it exhibits no pleochroism when viewed through a calcite dichroscope, something that would be expected in a corundum of this hue and depth of color.
Magnification
Diffused transmitted lighting reveals that the stone has been surface coated. Irregularities in the coating—scratches and pits on pavilion facets as well as abrasions on facet junctions---indicate that this is an essentially colorless stone. Examination in surface reflected lighting reveals a predominantly purple iridescence on pavilion facets.
Additional testing
The ultraviolet visible absorption spectrum was found to be similar to that of natural color yellow sapphire with features related to Fe3+. A qualitative chemical analysis performed by EDXRF reveals the presence of iron as the dominating trace element, with small amounts of potassium, calcium, titanium and gallium. Neither ultraviolet visible absorption spectroscopy nor X-ray fluorescence helped to detect or characterize the coating.
Discussion
The microscope features of this stone show it to have been coated, with the coating being responsible for both the apparent body color and superficial iridescence. It is important to note that this is a surface coating and not a diffusion treatment.
‘Aqua Aura’ is the trade name used for a type of coated gem seen for some time now. This consists of such materials as unfashioned rock crystal specimen as well as faceted rock crystal and colorless topaz to which a thin layer of gold has been applied. The treatment produces a greenish blue apparent body color (the transmission color of the gold coating) and superficial iridescence. Treated gems of these type exhibit microscopic features like those described above. It is possible that the corundum described herein has been subjected to a similar coating but of a different substance.
Wednesday, April 25, 2007
Dyed Natural Corundum As A Ruby Imitation
(via ICA Early Warning Flash, No.50, December 11, 1991) SSEF writes:
The following observations were made in the SSEF laboratory and further during examination of stones by Dr K Schmetzer and Mr F J Schupp, Germany.
Submitted stone chains and faceted stones were consisting of a heavily fractured type of natural corundum material, probably stained during quench cracking. They were sold as originating from India. The flattened beads were up to 15mm in diameter, the faceted oval stones between 5 and 8 carats.
Closer examination under the microscope reveals that the red color is deposited on irregular fracture planes only. The material is colored by a violetish red stain, the result of an artificial fracture treatment. The color is similar to the color of somewhat dark ruby and makes a convincing ruby imitation.
The stones show natural inclusions which consist of sets of parallel twin lamellae in one or two directions, forming straight intersection lines. Boehmite particles are confined to these intersection lines. Small double refractive mineral inclusions forming clusters were also observed. Stones with similar properties are known by us to come from East Africa. In immersion, light yellow or greenish yellow portions are forming areas between the fractures, showing the original color of the material. The red color is only seen in fractures. In thick pieces, the artificial treatment (i.e the stained fractures) is more difficult to see.
Beside of the above, the treated material can be recognized by a yellow fluorescence under long wave UV radiation. The red artificial color is said to fade after exposure of some weeks to daylight. Also the rather uneven color distribution on the fractures, as seen under magnification, is diagnostic.
The chromophore element of ruby is chromium. The easiest way to prove its presence in corundum is by observing the absorption spectrum with a pocket spectroscope. Chromium causes a prominent set of absorption lines and a fluorescence doublet in the red part of the spectrum. These characteristics are not visible in the dyed corundum since they lack chromium and therefore are not ruby.
The following observations were made in the SSEF laboratory and further during examination of stones by Dr K Schmetzer and Mr F J Schupp, Germany.
Submitted stone chains and faceted stones were consisting of a heavily fractured type of natural corundum material, probably stained during quench cracking. They were sold as originating from India. The flattened beads were up to 15mm in diameter, the faceted oval stones between 5 and 8 carats.
Closer examination under the microscope reveals that the red color is deposited on irregular fracture planes only. The material is colored by a violetish red stain, the result of an artificial fracture treatment. The color is similar to the color of somewhat dark ruby and makes a convincing ruby imitation.
The stones show natural inclusions which consist of sets of parallel twin lamellae in one or two directions, forming straight intersection lines. Boehmite particles are confined to these intersection lines. Small double refractive mineral inclusions forming clusters were also observed. Stones with similar properties are known by us to come from East Africa. In immersion, light yellow or greenish yellow portions are forming areas between the fractures, showing the original color of the material. The red color is only seen in fractures. In thick pieces, the artificial treatment (i.e the stained fractures) is more difficult to see.
Beside of the above, the treated material can be recognized by a yellow fluorescence under long wave UV radiation. The red artificial color is said to fade after exposure of some weeks to daylight. Also the rather uneven color distribution on the fractures, as seen under magnification, is diagnostic.
The chromophore element of ruby is chromium. The easiest way to prove its presence in corundum is by observing the absorption spectrum with a pocket spectroscope. Chromium causes a prominent set of absorption lines and a fluorescence doublet in the red part of the spectrum. These characteristics are not visible in the dyed corundum since they lack chromium and therefore are not ruby.
Vietnamese Ruby Salted With Synthetic Ruby
(via ICA Early Warning Flash, no.22, March 27, 1992) Grahame Brown writes:
Background
Following the discovery of alluvial ruby in Vietnam in the late 80s, small parcels of distinctively colored purplish pink to purplish red rough, as well as some cut stones, became available for purchase in Australia in early 1990. Initially the major sellers of this ruby appeared to be Vietnamese residents of Australia. Subsequently, Australian gem merchants purchased parcels of Vietnamese ruby, in Bangkok, for resale in Australia.
Over the last year I have been requested to examine several parcels of Vietnamese ruby rough, as well as some small parcels of faceted Vietnamese ruby, to establish the natural origin of this ruby. This alert has been issued in response to my findings.
Observed features
The rough examined appeared to be water worn, and sometimes displayed visually convincing evidence of external crystal forms, and parting planes. The few unabraded fracture surfaces and parting planes on the surface of this rough allowed very limited visual access to its interior.
Suspicious were immediately raised when some of the rubies, faceted from allegedly Vietnamese ruby rough, displayed:
- diffused curved color banding
- curving empty surface reaching fractures
- profiled gas bubbles and closely associated whitish granular masses
Of these inclusions, the curved color banding was most difficult to detect. Visibility of this curved color banding was enhanced when the immersed ruby was rotated in diffused transmitted light generated from a laterally directed fibre optic wand.
As diffused curved color banding and curving surface reaching fractures characterize heat treated Verneuil synthetic ruby, and profiled bubbles and whitish granular partly melted alumina powder are not uncommonly found in the sintered area of attachment between the Verneuil boule and the ceramic pedestal of the chalumeau……a hypothesis that some parcels of Vietnamese ruby rough were being salted with rough shaped, tumbled, heat treated Verneuil synthetic ruby seems possible.
As some of these inclusions were also observed in small parcels of faceted Vietnamese ruby, buyers of this new exciting should exercise caution.
Background
Following the discovery of alluvial ruby in Vietnam in the late 80s, small parcels of distinctively colored purplish pink to purplish red rough, as well as some cut stones, became available for purchase in Australia in early 1990. Initially the major sellers of this ruby appeared to be Vietnamese residents of Australia. Subsequently, Australian gem merchants purchased parcels of Vietnamese ruby, in Bangkok, for resale in Australia.
Over the last year I have been requested to examine several parcels of Vietnamese ruby rough, as well as some small parcels of faceted Vietnamese ruby, to establish the natural origin of this ruby. This alert has been issued in response to my findings.
Observed features
The rough examined appeared to be water worn, and sometimes displayed visually convincing evidence of external crystal forms, and parting planes. The few unabraded fracture surfaces and parting planes on the surface of this rough allowed very limited visual access to its interior.
Suspicious were immediately raised when some of the rubies, faceted from allegedly Vietnamese ruby rough, displayed:
- diffused curved color banding
- curving empty surface reaching fractures
- profiled gas bubbles and closely associated whitish granular masses
Of these inclusions, the curved color banding was most difficult to detect. Visibility of this curved color banding was enhanced when the immersed ruby was rotated in diffused transmitted light generated from a laterally directed fibre optic wand.
As diffused curved color banding and curving surface reaching fractures characterize heat treated Verneuil synthetic ruby, and profiled bubbles and whitish granular partly melted alumina powder are not uncommonly found in the sintered area of attachment between the Verneuil boule and the ceramic pedestal of the chalumeau……a hypothesis that some parcels of Vietnamese ruby rough were being salted with rough shaped, tumbled, heat treated Verneuil synthetic ruby seems possible.
As some of these inclusions were also observed in small parcels of faceted Vietnamese ruby, buyers of this new exciting should exercise caution.
Blue Diffusion Treated Synthetic Sapphires
(via ICA Early Warning Flash, No.55, June 2, 1992) GIA GTL writes:
Background
Recently the GIA Gem Trade Laboratory, Inc facilities in both Santa Monica, California, and New York, received for identification parcels of faceted stones that were determined to have been diffusion-treated to produce a blue coloration. In one instance, gemological investigation revealed that all three treated stones were synthetic sapphires. In a second instance, a parcel of about 40 stones was determined to consist of approximately 2/3 natural corundums and 1/3 synthetic corundums.
Visible observations/magnification
Examination using immersion with diffused transmitted illumination revealed features characteristic of stone color enhanced through diffusion treatment; for a summary of diagnostic properties, see ‘The Identification of Blue Diffusion Treated Sapphires’ (Kane et al) in the summer 1990 issue of Gems & Gemology.
Using magnification and darkfield illumination it was possible to detect the presence of various inclusions in a number of the stones that identified these hosts as being of natural origin. In other specimens, the presence of gas bubbles proved the hosts to be synthetic. Some stones, however, exhibited no diagnostic features through microscopic examination.
Plato test
The Plato test was also used in the determination of natural vs synthetic origin. A positive Plato test, further substantiating synthetic origin, was obtained with most of the stones identified as synthetic by virtue of diagnostic inclusions, as well as with those specimens without any such internal features. It should be noted, however, that characteristic positive Plato test appearance was generally more subtle than what we are accustomed to seeing.
Ultraviolet luminescence
Examination under both long and short wave ultraviolet radiation revealed some additional potentially useful information. In many cases, the diffusion treated stones exhibited some small areas where there was no blue diffused color, most likely due to this having been removed in repolishing after diffusion treatment. Under long wave UV radiation, these areas on a number of the blue diffusion treated natural sapphires fluoresced reddish orange, a reaction often associated with colorless to light blue corundum from Sri Lanka. When exposed to short wave UV, these same areas fluoresced a chalky whitish blue, a reaction associated with some sapphires that have been exposed to high temperature treatments.
The synthetic sapphires, however, were are all completely inert to long wave UV radiation, including areas where the blue diffusion treated coloration was absent; these areas fluoresced a chalky whitish blue to short wave UV. Such luminescent reactions may be exhibited by colorless synthetic sapphires. While the short wave reactions of both natural and synthetic sapphires were similar in these cases, the effect was slightly stronger with the synthetic samples. It should be noted, however, that the strength of fluorescent reactions in natural, synthetic, and treated sapphires can vary considerably.
Discussion
Immersion used in conjunction with diffused, transmitted illumination is generally quite effective in detecting the presence of diffusion treated color in corundum. Detecting this enhancement, however, does not prove or even indicate whether the treated gem material is of natural or synthetic origin. In the above examples, a combination of magnification and Plato test were used to make this determination.
Ultraviolet luminescence provided some additional, potentially useful information. In this regard, it should be noted that the presence of the reddish orange long wave reaction may be considered a good indication that the starting material is natural; although the absence of such a reaction indicates neither natural nor synthetic origin.
Background
Recently the GIA Gem Trade Laboratory, Inc facilities in both Santa Monica, California, and New York, received for identification parcels of faceted stones that were determined to have been diffusion-treated to produce a blue coloration. In one instance, gemological investigation revealed that all three treated stones were synthetic sapphires. In a second instance, a parcel of about 40 stones was determined to consist of approximately 2/3 natural corundums and 1/3 synthetic corundums.
Visible observations/magnification
Examination using immersion with diffused transmitted illumination revealed features characteristic of stone color enhanced through diffusion treatment; for a summary of diagnostic properties, see ‘The Identification of Blue Diffusion Treated Sapphires’ (Kane et al) in the summer 1990 issue of Gems & Gemology.
Using magnification and darkfield illumination it was possible to detect the presence of various inclusions in a number of the stones that identified these hosts as being of natural origin. In other specimens, the presence of gas bubbles proved the hosts to be synthetic. Some stones, however, exhibited no diagnostic features through microscopic examination.
Plato test
The Plato test was also used in the determination of natural vs synthetic origin. A positive Plato test, further substantiating synthetic origin, was obtained with most of the stones identified as synthetic by virtue of diagnostic inclusions, as well as with those specimens without any such internal features. It should be noted, however, that characteristic positive Plato test appearance was generally more subtle than what we are accustomed to seeing.
Ultraviolet luminescence
Examination under both long and short wave ultraviolet radiation revealed some additional potentially useful information. In many cases, the diffusion treated stones exhibited some small areas where there was no blue diffused color, most likely due to this having been removed in repolishing after diffusion treatment. Under long wave UV radiation, these areas on a number of the blue diffusion treated natural sapphires fluoresced reddish orange, a reaction often associated with colorless to light blue corundum from Sri Lanka. When exposed to short wave UV, these same areas fluoresced a chalky whitish blue, a reaction associated with some sapphires that have been exposed to high temperature treatments.
The synthetic sapphires, however, were are all completely inert to long wave UV radiation, including areas where the blue diffusion treated coloration was absent; these areas fluoresced a chalky whitish blue to short wave UV. Such luminescent reactions may be exhibited by colorless synthetic sapphires. While the short wave reactions of both natural and synthetic sapphires were similar in these cases, the effect was slightly stronger with the synthetic samples. It should be noted, however, that the strength of fluorescent reactions in natural, synthetic, and treated sapphires can vary considerably.
Discussion
Immersion used in conjunction with diffused, transmitted illumination is generally quite effective in detecting the presence of diffusion treated color in corundum. Detecting this enhancement, however, does not prove or even indicate whether the treated gem material is of natural or synthetic origin. In the above examples, a combination of magnification and Plato test were used to make this determination.
Ultraviolet luminescence provided some additional, potentially useful information. In this regard, it should be noted that the presence of the reddish orange long wave reaction may be considered a good indication that the starting material is natural; although the absence of such a reaction indicates neither natural nor synthetic origin.
Tuesday, April 24, 2007
Synthetic Green Quartz
(via ICA Early Warning Flash, No. 63, November 17, 1992) GIA GTL writes:
Background
At the Tucson Gem and Mineral shows in February of 1991, we noted dealers offering large quantities of synthetic quartz, reportedly of Russian origin. Among these was a transparent dark green type that visually resembles tourmaline. This green synthetic quartz was also being offered at the Tucson shows this past February; it was our impression that even more faceted material was being offered this year.
Recently, the GIA Gem Trade Laboratory, Inc in Santa Monica received for identification from two separate clients faceted specimens of what we identified as dark green synthetic quartz. In both cases, the material has been represented to our clients as a new type of natural green quartz from Brazil.
Gemological properties
Gemological testing revealed refractive indices, birefringence, and specific gravity consistent with quartz, both natural and synthetic. The specimens were inert to both long and short wave ultraviolet radiation.
Examination under immersion between crossed polaroids shows that the material was untwined, with a bulls eye optical interference figure. Under magnification we noted parallel green color banding similar to that seen in a reference sample of synthetic green quartz of Russian origin. Also noted was some angular brown color zoning that ran perpendicular to the green banding, a feature we have noted in other colors of hydrothermal synthetic quartz. One specimen also contained numerous tiny white pinpoint inclusions of undetermined origin.
Chemistry
Energy Dispersive X-ray fluorescence detected the presence of silicon, potassium, and iron. This differed only slightly from the chemistry of the synthetic green quartz reference specimen. It is believed that the iron detected is responsible for the green coloration.
Discussion
In the above cases, the client’s specimens were all identified as synthetic green quartz. It is important to note that, while green quartz does occur in nature (and is sometimes referred to as praseolite or prasiolita), such material is typically light in tone. To our knowledge, natural green quartz with this depth of color has not been reported.
Background
At the Tucson Gem and Mineral shows in February of 1991, we noted dealers offering large quantities of synthetic quartz, reportedly of Russian origin. Among these was a transparent dark green type that visually resembles tourmaline. This green synthetic quartz was also being offered at the Tucson shows this past February; it was our impression that even more faceted material was being offered this year.
Recently, the GIA Gem Trade Laboratory, Inc in Santa Monica received for identification from two separate clients faceted specimens of what we identified as dark green synthetic quartz. In both cases, the material has been represented to our clients as a new type of natural green quartz from Brazil.
Gemological properties
Gemological testing revealed refractive indices, birefringence, and specific gravity consistent with quartz, both natural and synthetic. The specimens were inert to both long and short wave ultraviolet radiation.
Examination under immersion between crossed polaroids shows that the material was untwined, with a bulls eye optical interference figure. Under magnification we noted parallel green color banding similar to that seen in a reference sample of synthetic green quartz of Russian origin. Also noted was some angular brown color zoning that ran perpendicular to the green banding, a feature we have noted in other colors of hydrothermal synthetic quartz. One specimen also contained numerous tiny white pinpoint inclusions of undetermined origin.
Chemistry
Energy Dispersive X-ray fluorescence detected the presence of silicon, potassium, and iron. This differed only slightly from the chemistry of the synthetic green quartz reference specimen. It is believed that the iron detected is responsible for the green coloration.
Discussion
In the above cases, the client’s specimens were all identified as synthetic green quartz. It is important to note that, while green quartz does occur in nature (and is sometimes referred to as praseolite or prasiolita), such material is typically light in tone. To our knowledge, natural green quartz with this depth of color has not been reported.
Synthetic Green Quartz
(via ICA Early Warning Flash, No. 63, November 17, 1992) GIA GTL writes:
Background
At the Tucson Gem and Mineral shows in February of 1991, we noted dealers offering large quantities of synthetic quartz, reportedly of Russian origin. Among these was a transparent dark green type that visually resembles tourmaline. This green synthetic quartz was also being offered at the Tucson shows this past February; it was our impression that even more faceted material was being offered this year.
Recently, the GIA Gem Trade Laboratory, Inc in Santa Monica received for identification from two separate clients faceted specimens of what we identified as dark green synthetic quartz. In both cases, the material has been represented to our clients as a new type of natural green quartz from Brazil.
Gemological properties
Gemological testing revealed refractive indices, birefringence, and specific gravity consistent with quartz, both natural and synthetic. The specimens were inert to both long and short wave ultraviolet radiation.
Examination under immersion between crossed polaroids shows that the material was untwined, with a bulls eye optical interference figure. Under magnification we noted parallel green color banding similar to that seen in a reference sample of synthetic green quartz of Russian origin. Also noted was some angular brown color zoning that ran perpendicular to the green banding, a feature we have noted in other colors of hydrothermal synthetic quartz. One specimen also contained numerous tiny white pinpoint inclusions of undetermined origin.
Chemistry
Energy Dispersive X-ray fluorescence detected the presence of silicon, potassium, and iron. This differed only slightly from the chemistry of the synthetic green quartz reference specimen. It is believed that the iron detected is responsible for the green coloration.
Discussion
In the above cases, the client’s specimens were all identified as synthetic green quartz. It is important to note that, while green quartz does occur in nature (and is sometimes referred to as praseolite or prasiolita), such material is typically light in tone. To our knowledge, natural green quartz with this depth of color has not been reported.
Background
At the Tucson Gem and Mineral shows in February of 1991, we noted dealers offering large quantities of synthetic quartz, reportedly of Russian origin. Among these was a transparent dark green type that visually resembles tourmaline. This green synthetic quartz was also being offered at the Tucson shows this past February; it was our impression that even more faceted material was being offered this year.
Recently, the GIA Gem Trade Laboratory, Inc in Santa Monica received for identification from two separate clients faceted specimens of what we identified as dark green synthetic quartz. In both cases, the material has been represented to our clients as a new type of natural green quartz from Brazil.
Gemological properties
Gemological testing revealed refractive indices, birefringence, and specific gravity consistent with quartz, both natural and synthetic. The specimens were inert to both long and short wave ultraviolet radiation.
Examination under immersion between crossed polaroids shows that the material was untwined, with a bulls eye optical interference figure. Under magnification we noted parallel green color banding similar to that seen in a reference sample of synthetic green quartz of Russian origin. Also noted was some angular brown color zoning that ran perpendicular to the green banding, a feature we have noted in other colors of hydrothermal synthetic quartz. One specimen also contained numerous tiny white pinpoint inclusions of undetermined origin.
Chemistry
Energy Dispersive X-ray fluorescence detected the presence of silicon, potassium, and iron. This differed only slightly from the chemistry of the synthetic green quartz reference specimen. It is believed that the iron detected is responsible for the green coloration.
Discussion
In the above cases, the client’s specimens were all identified as synthetic green quartz. It is important to note that, while green quartz does occur in nature (and is sometimes referred to as praseolite or prasiolita), such material is typically light in tone. To our knowledge, natural green quartz with this depth of color has not been reported.
Maxixe Type Beryls
(via ICA Early Warning Flash, No.72, July 29, 1993) Grahame Brown writes:
Preamble
Maxixe-type beryls are potentially color fading, strongly hued blue, green, blue green, yellow green, and yellow beryls that have been created by irradiation and selective heat treatment of previously pale to light colored beryl that has a very specific precursor color center.
Although the identifying features of color fading deep blue and deep green Maxixe-type beryls have been known since the early 1970s, little information has been published about the identifying features of color fading strongly hued greenish yellow to yellow green Maxixe-type beryls, or more importantly, somewhat color stable yellow Maxixe-type beryls.
While dark blue and less common dark green Maxixe-type beryls first appeared on world gem markets about 20 years ago, the recent appearance of well faceted, large size (<20 ct), eye clean, strongly hued greenish yellow, yellow green, and yellow Maxixe-type beryls may indicate renewed interest in the manufacture of these color enhanced beryls.
Identification
Irrespective of color, or whether or not the rough has or has not been oriented to display best color through the table of the faceted beryl, Maxixe-type beryls can be identified by:
An essential first step:
Using a conoscope, or equivalent gemological instrument such as a Snow Figure-O-Scope to accurately locate the optic axis (direction of single refraction or direction of the ordinary ray) in the suspect beryl.
As essential second step:
Examine the beryl, in the direction of its ordinary ray, with a hand-held dichroscope. If the beryl is a Maxixe-type, two adjacent dark color (of equal strength) will be observed. In contrast, if the beryl is a naturally colored aquamarine or heliodor, two light color (of equal strength) will be observed.
A confirmatory third step:
Examine the beryl, in the direction of its ordinary ray, with a prism or diffraction grating spectroscope. If the beryl is not examined, precisely along the direction of its ordinary ray, identifying Maxixe-type absorptions, that consist of a distinctive pattern of narrow absorptions of varying strength between 700nm (red) and 550nm (green), may not be observed.
Fade testing by exposing the suspect beryl to intense sunlight for more than a week, or by heating it for 30 minutes at 200-450 F, or by exposing it to a 100 W incandescent light bulb for 150 hours at a distance of 15cm, is an undesirable, destructive form of gem testing.
Consequently this ultimate test of fading potential is unlikely to be applied, except in the research laboratory.
However, in spite of this obvious limitation, fade testing does not provide the ultimate test for color stability. Under any of the fade testing conditions specified above:
Deep blue Maxixe-type beryls do not fade rapidly, and dramatically.
Greenish yellow to yellow green Maxixe-type beryls essentially loose their greenish component and fade to a yellowish hue.
Yellow Maxixe-type beryls loose any green component in their color, and may also fade.
Preamble
Maxixe-type beryls are potentially color fading, strongly hued blue, green, blue green, yellow green, and yellow beryls that have been created by irradiation and selective heat treatment of previously pale to light colored beryl that has a very specific precursor color center.
Although the identifying features of color fading deep blue and deep green Maxixe-type beryls have been known since the early 1970s, little information has been published about the identifying features of color fading strongly hued greenish yellow to yellow green Maxixe-type beryls, or more importantly, somewhat color stable yellow Maxixe-type beryls.
While dark blue and less common dark green Maxixe-type beryls first appeared on world gem markets about 20 years ago, the recent appearance of well faceted, large size (<20 ct), eye clean, strongly hued greenish yellow, yellow green, and yellow Maxixe-type beryls may indicate renewed interest in the manufacture of these color enhanced beryls.
Identification
Irrespective of color, or whether or not the rough has or has not been oriented to display best color through the table of the faceted beryl, Maxixe-type beryls can be identified by:
An essential first step:
Using a conoscope, or equivalent gemological instrument such as a Snow Figure-O-Scope to accurately locate the optic axis (direction of single refraction or direction of the ordinary ray) in the suspect beryl.
As essential second step:
Examine the beryl, in the direction of its ordinary ray, with a hand-held dichroscope. If the beryl is a Maxixe-type, two adjacent dark color (of equal strength) will be observed. In contrast, if the beryl is a naturally colored aquamarine or heliodor, two light color (of equal strength) will be observed.
A confirmatory third step:
Examine the beryl, in the direction of its ordinary ray, with a prism or diffraction grating spectroscope. If the beryl is not examined, precisely along the direction of its ordinary ray, identifying Maxixe-type absorptions, that consist of a distinctive pattern of narrow absorptions of varying strength between 700nm (red) and 550nm (green), may not be observed.
Fade testing by exposing the suspect beryl to intense sunlight for more than a week, or by heating it for 30 minutes at 200-450 F, or by exposing it to a 100 W incandescent light bulb for 150 hours at a distance of 15cm, is an undesirable, destructive form of gem testing.
Consequently this ultimate test of fading potential is unlikely to be applied, except in the research laboratory.
However, in spite of this obvious limitation, fade testing does not provide the ultimate test for color stability. Under any of the fade testing conditions specified above:
Deep blue Maxixe-type beryls do not fade rapidly, and dramatically.
Greenish yellow to yellow green Maxixe-type beryls essentially loose their greenish component and fade to a yellowish hue.
Yellow Maxixe-type beryls loose any green component in their color, and may also fade.
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