(via ICA Lab Alert, No.2, June 1987) AIGS writes:
During June of 1987, a very unusual composite ruby/synthetic ruby was brought in to the lab of AIGS for testing. It consisted of a piece of Verneuil synthetic ruby to which had been joined at the edge a smaller chunk of natural Burmese ruby. The whole stone was then faceted, concealing the join.
Two features are unusual about this stone. First of all, what appears to be glass has been used to join the two together. Gas bubbles were found in the glass area. Secondly, the edges of both the natural and synthetic areas were irregular. The use of glass to join the two together made this possible, as the glass-filled in the irregular surfaces. The entire stone showed signs of heat treatment, with induced fingerprints present in the synthetic section.
Detection
With the loupe or naked eye this stone could fool many people as the join looks like a crack and the natural area contained a large cloud of silk. However, immersion or overhead lighting will reveal the different luster of the glass join in the microscope. In addition, the synthetic portion displays curved striae and gas bubbles, as well as the induced fingerprints. The stone was purposely cut ‘native’ to imitate the appearance of a ruby just brought out from Burma.
Saturday, April 21, 2007
Plastic Coating Of Gemstones
(via ICA Lab Alert, No.3, 1987) AIGS writes:
Details
In the past 3 years, gemologists at AIGS in Bangkok have encountered an unusual type of assembled stone in which an inferior specimen is coated with colored plastic. All of the stones treated in this manner have been of Burmese origin and so it is believed that the treatment is probably done in Burma.
One type consists of a poor color jadeite cabochon coated with a thin layer of rich green plastic. The coating covers all surfaces of the cabochon except the bottom. After coating, the stone appears to be of very high quality.
Another type is a light color faceted ruby coated with red plastic and then repolished. This gives the appearance of a fine ruby.
The third type seen is a white star sapphire cabochon entirely coated with red plastic. The gem then appears like a beautiful star ruby.
Detection
Although extremely deceptive to the naked eye, these plastic coated stones are readily identified under magnification. They may be dangerous to the trade, though, because their appearance is so natural that unsuspecting dealer might not even check them with the loupe. One unaided clue is provided by the slightly warm and plastic-like feel of the stones. This, however, is very subtle.
Identification of plastic coating is made with the microscope. In the case of the jadeite, as the plastic does not cover the stone entirely, it may be seen to peel away from the stone in places along the girdle. In all types, gas bubbles may be visible in the plastic coating, particularly in the star ruby type, where the coating was thicker. Color swirls could also be seen in the star ruby type. Judicious use of the hot point will, of course, also reveal this fraud.
Details
In the past 3 years, gemologists at AIGS in Bangkok have encountered an unusual type of assembled stone in which an inferior specimen is coated with colored plastic. All of the stones treated in this manner have been of Burmese origin and so it is believed that the treatment is probably done in Burma.
One type consists of a poor color jadeite cabochon coated with a thin layer of rich green plastic. The coating covers all surfaces of the cabochon except the bottom. After coating, the stone appears to be of very high quality.
Another type is a light color faceted ruby coated with red plastic and then repolished. This gives the appearance of a fine ruby.
The third type seen is a white star sapphire cabochon entirely coated with red plastic. The gem then appears like a beautiful star ruby.
Detection
Although extremely deceptive to the naked eye, these plastic coated stones are readily identified under magnification. They may be dangerous to the trade, though, because their appearance is so natural that unsuspecting dealer might not even check them with the loupe. One unaided clue is provided by the slightly warm and plastic-like feel of the stones. This, however, is very subtle.
Identification of plastic coating is made with the microscope. In the case of the jadeite, as the plastic does not cover the stone entirely, it may be seen to peel away from the stone in places along the girdle. In all types, gas bubbles may be visible in the plastic coating, particularly in the star ruby type, where the coating was thicker. Color swirls could also be seen in the star ruby type. Judicious use of the hot point will, of course, also reveal this fraud.
Glass Infilling Of Cracks In Ruby
(via ICA Lab Alert, No. 4, June, 1987) AIGS writes:
Details
During the ICA Congress held recently in Bangkok, Dr Henri Hanni of Switzerland described to us a new ruby treatment. This consisted of poor quality African ruby cabochons whose cracks had been filled with glass. At the time of the Congress we had not yet seen these stones in Bangkok. In late June of 1987 we saw the first stone. It was a heavily included ruby cabochon, with many cracks that passed deep into the stone. These were filled with glass-like substance. This treatment differs from ordinary surface repaired rubies as the glass dos not just fill in surface pits, but instead appears to penetrate deep into the cracks.
Detection
This treatment is easily detected in the same manner as ordinary surface repaired rubies. Using overhead lighting, or immersion in methylene iodide, will reveal the glass filling due to its different luster or relief. If the opening of the crack is very narrow, however, the glass filling may be difficult to see. Gas bubbles may be found in some of the glass areas.
Dr K Schmetzer writes:
Kenyan rubies are also treated with plastics in order to improve the quality of the stones. In the treatment, cracks or fissures were filled with plastics which is sometimes deeply penetrating into the stones.
Details
During the ICA Congress held recently in Bangkok, Dr Henri Hanni of Switzerland described to us a new ruby treatment. This consisted of poor quality African ruby cabochons whose cracks had been filled with glass. At the time of the Congress we had not yet seen these stones in Bangkok. In late June of 1987 we saw the first stone. It was a heavily included ruby cabochon, with many cracks that passed deep into the stone. These were filled with glass-like substance. This treatment differs from ordinary surface repaired rubies as the glass dos not just fill in surface pits, but instead appears to penetrate deep into the cracks.
Detection
This treatment is easily detected in the same manner as ordinary surface repaired rubies. Using overhead lighting, or immersion in methylene iodide, will reveal the glass filling due to its different luster or relief. If the opening of the crack is very narrow, however, the glass filling may be difficult to see. Gas bubbles may be found in some of the glass areas.
Dr K Schmetzer writes:
Kenyan rubies are also treated with plastics in order to improve the quality of the stones. In the treatment, cracks or fissures were filled with plastics which is sometimes deeply penetrating into the stones.
Friday, April 20, 2007
Natural And Synthetic Yellow/Orange Sapphires
(via ICA Lab Alert, No. 5, December 1987) AIGS writes:
Subject
The detection of color banding/growth zoning in natural and synthetic yellow/orange sapphires.
Method
Color banding, either straight or curved, can be detected much more easily by using a technique developed at AIGS in 1981. This involves the use of a frosted (diffused) blue filter over the microscope’s light source.
When looking for color zoning in yellow sapphires, the usual practice is to immerse the stone in methylene iodide. However, with a yellow stone in a yellow liquid over a yellow (incandescent) light, there is little chance of finding yellow bands of color. Using a white (fluorescent) light helps a bit, but not enough. AIGS have found that by using a frosted blue filter it becomes a much more easier to locate color bands, either straight or curved, as blue is the color being absorbed the most in yellow stones. Sometimes we stack two or three blue filters on top of one another. Although this does not cut down on the light intensity, it still makes it much easier to locate the color zoning. Using the frosted blue filter plus immersion, it is possible to locate straight or curved color banding in about 95% or more of all natural and synthetic yellow/orange sapphires. Furthermore, a green filter can be used for rubies—the color of the should approximate the absorption maxima of the stone.
E Gubelin writes:
To use a frosted blue filter and examine the gem in immersion is an excellent suggestion (though known to experienced gemologist for many years already). The effect may be enhanced if one close the diaphragm to about half or about a quarter of its diameter below the immersion cell.
Subject
The detection of color banding/growth zoning in natural and synthetic yellow/orange sapphires.
Method
Color banding, either straight or curved, can be detected much more easily by using a technique developed at AIGS in 1981. This involves the use of a frosted (diffused) blue filter over the microscope’s light source.
When looking for color zoning in yellow sapphires, the usual practice is to immerse the stone in methylene iodide. However, with a yellow stone in a yellow liquid over a yellow (incandescent) light, there is little chance of finding yellow bands of color. Using a white (fluorescent) light helps a bit, but not enough. AIGS have found that by using a frosted blue filter it becomes a much more easier to locate color bands, either straight or curved, as blue is the color being absorbed the most in yellow stones. Sometimes we stack two or three blue filters on top of one another. Although this does not cut down on the light intensity, it still makes it much easier to locate the color zoning. Using the frosted blue filter plus immersion, it is possible to locate straight or curved color banding in about 95% or more of all natural and synthetic yellow/orange sapphires. Furthermore, a green filter can be used for rubies—the color of the should approximate the absorption maxima of the stone.
E Gubelin writes:
To use a frosted blue filter and examine the gem in immersion is an excellent suggestion (though known to experienced gemologist for many years already). The effect may be enhanced if one close the diaphragm to about half or about a quarter of its diameter below the immersion cell.
Plastic Treated Emeralds
(via ICA Lab Alert No. 6, August 13, 1987) Nubio Horiuchi writes:
Source
I have personally seen this treatment for the past three years in Japan (Central Gem Laboratory).
Status
Details of this have not been announced yet, but it is summarized as follows:
The fractures are first cleaned and then impregnated with some kind of liquid plastic. It is presumed that the liquid plastic is hardened by irradiation of light or ultraviolet rays.
Merit of this treatment
In normal oil treatment the oil will seep out during cleaning or over a period of normal wearing and there is a gradual loss of color and the fractures become noticeable. However, with the impregnation of liquid plastic the treatment is durable.It would appear from the durability standpoint that the liquid plastic treatment is better than oiling.
Identification
It is difficult to distinguish between oil and plastic treatments.
Question
In which category of enhancement and treatment should the plastic treated emeralds be classified?
E. Gubelin writes:
Though more durable the result of this new plastic treatment should become to known to all members immediately, because many members of the trade use an ultrasonic cleaning machine which causes the oil to be washed out. If no oil is being washed out, people might not become aware of the fact that the fractures are filled with plastic films. Despite the greater durability the stimulus for easier fraudulent practices does by no ways raise the ethical standard of this plastic treatment.
Dr K Schmetzer writes:
The stones should be classified as plastic-impregnated emeralds.
Source
I have personally seen this treatment for the past three years in Japan (Central Gem Laboratory).
Status
Details of this have not been announced yet, but it is summarized as follows:
The fractures are first cleaned and then impregnated with some kind of liquid plastic. It is presumed that the liquid plastic is hardened by irradiation of light or ultraviolet rays.
Merit of this treatment
In normal oil treatment the oil will seep out during cleaning or over a period of normal wearing and there is a gradual loss of color and the fractures become noticeable. However, with the impregnation of liquid plastic the treatment is durable.It would appear from the durability standpoint that the liquid plastic treatment is better than oiling.
Identification
It is difficult to distinguish between oil and plastic treatments.
Question
In which category of enhancement and treatment should the plastic treated emeralds be classified?
E. Gubelin writes:
Though more durable the result of this new plastic treatment should become to known to all members immediately, because many members of the trade use an ultrasonic cleaning machine which causes the oil to be washed out. If no oil is being washed out, people might not become aware of the fact that the fractures are filled with plastic films. Despite the greater durability the stimulus for easier fraudulent practices does by no ways raise the ethical standard of this plastic treatment.
Dr K Schmetzer writes:
The stones should be classified as plastic-impregnated emeralds.
New Treatment For Diamonds
(via ICA Lab Alert No.7, August 13, 1987) Nubo Horiuchi writes:
Source
I found this treatment in January 1987.
Status
This treatment makes cleavage cracks to the surface less visible by impregnating with unknown material. On looking through the cleavage crack of a diamond treated in this manner, a whitish appearance can be seen which improves the clarity grade of the diamond. Impregnating the cleavage crack of the diamond with this unknown material, which may be silicon oil, it is quite effective in improving the appearance of the cleavage crack because it reduces diffuse reflections. This treatment was located in the diamonds lots imported from Israel.
Identification
Upon looking through a diamond under a diamond light, a dark blue or rainbow hue of interference color will be seen under the diffused light.
Opinion
The organization of gem laboratories in Japan judges that diamonds enhanced in this manner are treated diamonds.
E.Gubelin writes:
It certainly is imperative that all members are informed about this new unethical treatment of diamonds because too many dealers might consider these artificially filled fractures as naturally lined fissures.
Youichi Horikawa writes:
I think identification of these treated diamonds is not easy, because the interference color can be seen in untreated diamonds also.
Source
I found this treatment in January 1987.
Status
This treatment makes cleavage cracks to the surface less visible by impregnating with unknown material. On looking through the cleavage crack of a diamond treated in this manner, a whitish appearance can be seen which improves the clarity grade of the diamond. Impregnating the cleavage crack of the diamond with this unknown material, which may be silicon oil, it is quite effective in improving the appearance of the cleavage crack because it reduces diffuse reflections. This treatment was located in the diamonds lots imported from Israel.
Identification
Upon looking through a diamond under a diamond light, a dark blue or rainbow hue of interference color will be seen under the diffused light.
Opinion
The organization of gem laboratories in Japan judges that diamonds enhanced in this manner are treated diamonds.
E.Gubelin writes:
It certainly is imperative that all members are informed about this new unethical treatment of diamonds because too many dealers might consider these artificially filled fractures as naturally lined fissures.
Youichi Horikawa writes:
I think identification of these treated diamonds is not easy, because the interference color can be seen in untreated diamonds also.
New Diamond Treatment
(via ICA Lab Alert No.8, August 14, 1987) GIA GTL writes:
The New York GIA GTL recently examined a group of diamonds which had undergone a ‘fill’ treatment to improve their appearance.
‘We were told the diamonds had been treated in Israel and that this process has been in use for some time,” said Bert Krashes. “In view of the obligation of the jeweler to disclose treatments, this procedure will be yet another challenge in terminology and explanation to the retail customer.”
Apparently, the treatment has been applied only to highly imperfect diamonds with flaws that open to the surface. By introducing a high refractive index fill into fractures and gletzes, they become dramatically less noticeable to the unaided eye. I2 and I3 grades, for example, are improved to an I1 appearance.
Under binocular magnification, the appearance of these cracks is different from untreated ones, showing white thread-like and pinpoint deposits similar to ‘fingerprint’ inclusions. In addition, an orangy brown reflection was observed in the surfaces reached by the cracks. This suggests the color of the filler used may be brownish, typical of high refractive liquids. It has been reported that the filler can be removed by soaking in aqua regia. The treatment is said to now be available in Antwerp as well as Israel.
“The examination was necessarily hurried and only a few diamonds were available to us; therefore this should be considered an alert rather than a definitive description,” said Krashes. “GIA is attempting to secure more of these diamonds for study and will issue a full report as soon as possible.”
The New York GIA GTL recently examined a group of diamonds which had undergone a ‘fill’ treatment to improve their appearance.
‘We were told the diamonds had been treated in Israel and that this process has been in use for some time,” said Bert Krashes. “In view of the obligation of the jeweler to disclose treatments, this procedure will be yet another challenge in terminology and explanation to the retail customer.”
Apparently, the treatment has been applied only to highly imperfect diamonds with flaws that open to the surface. By introducing a high refractive index fill into fractures and gletzes, they become dramatically less noticeable to the unaided eye. I2 and I3 grades, for example, are improved to an I1 appearance.
Under binocular magnification, the appearance of these cracks is different from untreated ones, showing white thread-like and pinpoint deposits similar to ‘fingerprint’ inclusions. In addition, an orangy brown reflection was observed in the surfaces reached by the cracks. This suggests the color of the filler used may be brownish, typical of high refractive liquids. It has been reported that the filler can be removed by soaking in aqua regia. The treatment is said to now be available in Antwerp as well as Israel.
“The examination was necessarily hurried and only a few diamonds were available to us; therefore this should be considered an alert rather than a definitive description,” said Krashes. “GIA is attempting to secure more of these diamonds for study and will issue a full report as soon as possible.”
Yellow Sapphire
(via ICA Lab Alert, No.9, September 1, 1987) Kurt Nassau writes:
Background
There are several types of natural yellow sapphires that are seen in the trade, including the untreated, the high temperature heated, and the irradiated ones. The first two are stable to light, while the third (irradiated either by nature or by man) fades in light. Natural yellow stones after being mined may fade on light exposure, and it is customary to expose such material to light or heat it. A heating test is also sometimes used to check yellow sapphire for fading: Webster recommends 230°C (446°F) for a few minutes and Nassau has used 200°C for one hour to establish a potential for fading in light in irradiated gemstones in general.
Observation
Ordinary yellow sapphire, that is the non-irradiated, non-heated, non-light fading, stable material can lose some color at as low as 60°C (140°F), more at higher temperatures, and all color by 600°C (1112°F). Quite unexpectedly, light has been found to reverse this change. It restores this type of yellow sapphire to its ‘proper’ stable color from either the dark irradiated state or from the lighter heated state. If heating has been performed accidentally, the color may be restored by exposure to bright light for a few days.
Recommendations
Do not use a heating test for any yellow sapphire. To test for irradiated stones, a light exposure test is the only one that can safely be recommended.
Reference
A fully detailed article by Kurt Nassau and G Kay Valente has been submitted for publication in Gems & Gemology under the title “The Seven Types of Yellow Sapphire and a Corundum Conurundum.”
Background
There are several types of natural yellow sapphires that are seen in the trade, including the untreated, the high temperature heated, and the irradiated ones. The first two are stable to light, while the third (irradiated either by nature or by man) fades in light. Natural yellow stones after being mined may fade on light exposure, and it is customary to expose such material to light or heat it. A heating test is also sometimes used to check yellow sapphire for fading: Webster recommends 230°C (446°F) for a few minutes and Nassau has used 200°C for one hour to establish a potential for fading in light in irradiated gemstones in general.
Observation
Ordinary yellow sapphire, that is the non-irradiated, non-heated, non-light fading, stable material can lose some color at as low as 60°C (140°F), more at higher temperatures, and all color by 600°C (1112°F). Quite unexpectedly, light has been found to reverse this change. It restores this type of yellow sapphire to its ‘proper’ stable color from either the dark irradiated state or from the lighter heated state. If heating has been performed accidentally, the color may be restored by exposure to bright light for a few days.
Recommendations
Do not use a heating test for any yellow sapphire. To test for irradiated stones, a light exposure test is the only one that can safely be recommended.
Reference
A fully detailed article by Kurt Nassau and G Kay Valente has been submitted for publication in Gems & Gemology under the title “The Seven Types of Yellow Sapphire and a Corundum Conurundum.”
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