2007: Here is an excellent insight to identification (diamond) from my mentor.
(via The Journal of Gemmology, Vol.XIX, N0.2, April 1984) Kenneth Scarratt writes:
It is not unusual for a group of gemologists to disagree over the color of gemstone. Some colored diamonds in particular tend to possess colors which are most difficult to describe. However, when you see a diamond actually change color from one distinct color to another before your eyes it can shake any confidence you may have in your own eyesight.
Such was the case when late one afternoon I decided to make start on identifying the nature (natural or treated) of the color of 2.02 ct brilliant-cut diamond. All I really had time for was to make out my worksheet, giving a full description of the stone, and a short microscopic examination before it had to go into the safe for the night. On the worksheet I stated in a most positive fashion that the color of the stone was green. The next morning when the safe was opened I immediately retrieved the envelope containing the diamond, took it to a work bench and removed the stone from it. There before me lay a brilliant yellow stone. After checking the envelope to make sure that it was the one I put in the safe the night before (it was) I decided to check the stone’s weight against my record, but as I picked it up to take it to the balance its color started to change through various shades of yellow and yellow/green until it was back to the color it was the night before.
These so-called ‘chameleon diamonds’ have been reported upon before, and the change has been variously described as being associated with changes in temperature or in the amount of light reaching the stone. A manufacturer would notice the effect because it is said that these stones glow red on ‘the wheel’ and change to yellow shortly afterwards, from which they return to their normal green at room temperature; whereas a trader might become aware of the type of stone he had in a similar manner to that in which I had become aware of the peculiarities of this stone.
The color change from green to yellow, unless one includes the slight cooling which may occur if the stone is placed in a safe overnight, is usually described as being dependant upon a temperature increase, such as placing the stone on a hot plate, rather than a decrease; and so it was interesting to discover that when we reduced the temperature of this stone to at first 120K in the laboratory and then to 77K at King’s College, London, whilst recording the spectra, the color of this stone once again became a brilliant yellow.
The differences between the room and low temperature spectra are quite evident. The general appearance of the spectrum at room temperature is approaching that of a normal Type 1b with a weak 415 (Type 1a) peering out of the gloom and an unusual absorption hump covering the yellow, orange, red and N.I.R—the are of greatest transmission being in the green. At the lower temperatures there is clearly a sharpening up of the 415, but more importantly there is a lessening of the absorption hump in the red, orange and yellow, allowing the stone to transmit to a greater extent in this region as well as in the green, thus resulting in a yellow stone.
One assumes that changes of a similar nature may take place when the stone is heated; however, we restricted ourselves to room and low temperature spectroscopy only. The luminescence effects produced by this tone were—long wave ultraviolet, a very strong bright yellow followed by a very strong greenish phosphorescence; short wave ultraviolet, a strong and bright yellow/green followed by a very strong greenish phosphorescence; and X-rays, a blue/green followed by a strong green phosphorescence.
Wednesday, July 18, 2007
Euclase
Chemistry: Berylium aluminum silicate
Crystal system: Monoclinic; prisms with numerous smooth faces; tabular, well developed.
Color: Transparent; colorless, pale green, light blue, sapphire blue (rare); may be color zoned
Hardness: 7.5
Cleavage: Perfect: 1 direction; Fracture: brittle, conchoidal to uneven.
Specific gravity: 3.10
Refractive index: 1.652 – 1.672; Biaxial positive; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak.
Occurrence: Russia, Africa, Brazil.
Notes
Collector’s stone; name refers to its easy cleavage; may look like aquamarine and green spodumene, but D.R and S.G different; spectra in deep colors: 2 vague bands in blue 468 and 455nm, may also show line in red 705nm; difficult to cut; faceted.
Crystal system: Monoclinic; prisms with numerous smooth faces; tabular, well developed.
Color: Transparent; colorless, pale green, light blue, sapphire blue (rare); may be color zoned
Hardness: 7.5
Cleavage: Perfect: 1 direction; Fracture: brittle, conchoidal to uneven.
Specific gravity: 3.10
Refractive index: 1.652 – 1.672; Biaxial positive; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak.
Occurrence: Russia, Africa, Brazil.
Notes
Collector’s stone; name refers to its easy cleavage; may look like aquamarine and green spodumene, but D.R and S.G different; spectra in deep colors: 2 vague bands in blue 468 and 455nm, may also show line in red 705nm; difficult to cut; faceted.
Tuesday, July 17, 2007
Shell Game Pilot
Memorable quotes from the movie:
Dinah (Margot Kidder): I was in Bogota, and I stumbled over this jerk drug dealer named Pavon, and... he just looked like he deserved to be taken, so... I sold him the Marie Antoinette diamonds.
Riley (James Read): You're still selling the Antoinettes? Those - those earrings were over-exposed years ago!
Dinah (Margot Kidder): In Europe, not in South America! It's a whole new market!
Riley (James Read): So what happened?
Dinah (Margot Kidder): Well, Pavon gave 'em to his girlfriend, and - and before she got 'em outta the box, she yelled, "Cubic zirconia..."
Dinah (Margot Kidder): I was in Bogota, and I stumbled over this jerk drug dealer named Pavon, and... he just looked like he deserved to be taken, so... I sold him the Marie Antoinette diamonds.
Riley (James Read): You're still selling the Antoinettes? Those - those earrings were over-exposed years ago!
Dinah (Margot Kidder): In Europe, not in South America! It's a whole new market!
Riley (James Read): So what happened?
Dinah (Margot Kidder): Well, Pavon gave 'em to his girlfriend, and - and before she got 'em outta the box, she yelled, "Cubic zirconia..."
Surviving The World Of Wine Etiquette
(via Indiatimes News Network) Reshmi R Dasgupta writes about the arcane world of wine etiquette @ http://economictimes.indiatimes.com/Surviving_the_world_of_wine_etiquette_/articleshow/2203459.cms
A Proper Temple
Economist writes about Indian modern art + Kolkata Museum of Modern Art, or KMoMA + other viewpoints @ http://www.economist.com/displayStory.cfm?story_id=9495928&fsrc=RSS
Tycoon Turf
(via The Irrawaddy) Aung Zaw writes about today's Burma + the two groups of people that govern the country + other viewpoints @ http://www.irrawaddy.org/article.php?art_id=5010
Coveting The Colored
Idexonline writes about colored diamonds + the way colored diamond dealers describe their stones + their scarcity and beauty + why the jewelers spend their lifetime hoping to hold and caress one of these extraordinary gems + other viewpoints @ http://www.idexonline.com/portal_FullMazalUbracha.asp?id=22694
The Pleasures Of Discovery
(via The Journal of Gemmology, Vol.XIV, No.3, July 1974) B W Anderson writes:
(being the substance of a talk given to the Gemmological Association of Great Britain at Goldsmith’s Hall on 29th October, 1973)
Ekanite
For the last of my stones we return to the gem gravels of Ceylon, and once more it was a keen gemologist who set the ball rolling. This was Mr F L D Ekanayake of Colombo, Ceylon, who, in 1953, sent a round cabochon dark green stone showing a faint four-rayed asterism to his friend, Mr R K Mitchell, accompanied by a letter in which he stated ‘I am sure this is a new mineral’. After some preliminary work Mr Mitchell allowed us to try our hand at solving the mystery of this peculiar stone. It appeared to be quite amorphous not only optically but to an X-ray beam, and yet the tiny oriented needles to which the asterism was due argued some degree of crystallinity. The density was 3.28 and R.I 1.60.
An attempt at spectrum analysis in the laboratory showed the presence of calcium, silica, and traces of lead. This last made me think in terms of glass, and I sent the stone to D K Hill, a well-known glass technologist, for his opinion. He at first confirmed the glass hypothesis, but then discovered by a much more skilled spectrum analysis than we could muster, that thorium was a major constituent of the material. Hill’s estimate was about 26 or 27% thorium oxide—which later proved to be almost exactly correct. On hearing this news the penny dropped, and I realized that we are dealing with a metamict—a crystal the structure of which had broken down due to 600 million years or so of internal bombardment with alpha particles, as in the case of the green metamict zircons we already knew so well. The trace of lead was also explained—this was the end product of the disintegration of thorium.
During this prolonged investigation, by another of those extraordinary chances of which I have already spoken, Mr Solomon, who was at the time an instructor of students of gemology in Plymouth, sent me a cabochon stone of this same metamict mineral, asking if I could tell what it was since it had puzzled his students. When I told him the story he kindly gave me the specimen.
As one could expect, Ekanayake’s stone proved to be quite strongly radioactive, leaving a trace after being placed on a photographic film for a few hours. Using a slice taken from the stone, we tried to return it to its original crystalline state by heat treatment: but heating at 1000ºC failed to bring about the hoped for alteration and transformed the stone into an opaque putty-colored mass.
It was several years before the Museum could proceed with the necessary complete analysis, which entailed a formidable piece of work and in the meantime Ekayanake had recovered three further pieces of the mineral from the same gem pit where the original was found—at Eheliyagoda near Ratnapura.
The final analyis, carried out by D I Bothwell, showed the new mineral to be essentially a silicate of thorium and calcium, though about 2% of uranium was also present. A preliminary note was published in Nature on June 10th, 1961, establishing the new mineral at last, and appropriately honoring its discoverer in the name Ekanite. R K Mitchell gave an excellent account of the long drawn out investigation in the Journal of Gemmology, and shortly afterwards Dr Edward Gubelin who, unknown to us, had been working intensively on the new mineral, of which he had acquired no fewer than 12 specimens, published a long and brilliant paper on the subject in Gems and Gemology, The Gemmologist, and elsewhere, which precluded the need for any further work on our part.
Since that time, crystallized forms of ekanite have been reported from Central Asia by Russian workers and from Saint-Hilaire, Quebec Province, in pegmatite veins. The crystals are tetragonal. The reason for these not having been reduced to the metamict stage lies in their much younger geological age—60 million years against 600 million.
One thing that took away much of the pleasure from these investigations into new gem minerals was the long delay between the initial burst of ordinary gemological work on the stones and the final necessary chemical analysis and crystal structure analysis which had to be performed before the mineral could be properly established and the conclusions published a scientific paper. One could not very well press for speed from the skilled Museum workers, for work which involved a great deal of time and effort, which had to be added to their own research programmes and routine work for the department. And we ourselves in the laboratory found it increasingly hard to find time to work continuously on any project as the demands of essential daily testing work became more and more pressing. Visits to the library became lunch-time snatches, and one felt guilty in doing any work which could be termed purely academic. And most of you know how hard it is to pick up the threads of any piece of work which has been put on a shelf and allowed to grow cold.
Amongst the advantages of such pieces of research are the sharpening of technical skills, an increased international reputation for the laboratory and a closer liaison with mineralogists—a liaison which is vital in the present state of our science.
For those of you who have found my topic for this evening too remote from everyday experiences and problems in the trade to interest you, I can promise a thoroughly down-to-earth talk next October, when I understand that I am going to be allowed to speak to you again.
(being the substance of a talk given to the Gemmological Association of Great Britain at Goldsmith’s Hall on 29th October, 1973)
Ekanite
For the last of my stones we return to the gem gravels of Ceylon, and once more it was a keen gemologist who set the ball rolling. This was Mr F L D Ekanayake of Colombo, Ceylon, who, in 1953, sent a round cabochon dark green stone showing a faint four-rayed asterism to his friend, Mr R K Mitchell, accompanied by a letter in which he stated ‘I am sure this is a new mineral’. After some preliminary work Mr Mitchell allowed us to try our hand at solving the mystery of this peculiar stone. It appeared to be quite amorphous not only optically but to an X-ray beam, and yet the tiny oriented needles to which the asterism was due argued some degree of crystallinity. The density was 3.28 and R.I 1.60.
An attempt at spectrum analysis in the laboratory showed the presence of calcium, silica, and traces of lead. This last made me think in terms of glass, and I sent the stone to D K Hill, a well-known glass technologist, for his opinion. He at first confirmed the glass hypothesis, but then discovered by a much more skilled spectrum analysis than we could muster, that thorium was a major constituent of the material. Hill’s estimate was about 26 or 27% thorium oxide—which later proved to be almost exactly correct. On hearing this news the penny dropped, and I realized that we are dealing with a metamict—a crystal the structure of which had broken down due to 600 million years or so of internal bombardment with alpha particles, as in the case of the green metamict zircons we already knew so well. The trace of lead was also explained—this was the end product of the disintegration of thorium.
During this prolonged investigation, by another of those extraordinary chances of which I have already spoken, Mr Solomon, who was at the time an instructor of students of gemology in Plymouth, sent me a cabochon stone of this same metamict mineral, asking if I could tell what it was since it had puzzled his students. When I told him the story he kindly gave me the specimen.
As one could expect, Ekanayake’s stone proved to be quite strongly radioactive, leaving a trace after being placed on a photographic film for a few hours. Using a slice taken from the stone, we tried to return it to its original crystalline state by heat treatment: but heating at 1000ºC failed to bring about the hoped for alteration and transformed the stone into an opaque putty-colored mass.
It was several years before the Museum could proceed with the necessary complete analysis, which entailed a formidable piece of work and in the meantime Ekayanake had recovered three further pieces of the mineral from the same gem pit where the original was found—at Eheliyagoda near Ratnapura.
The final analyis, carried out by D I Bothwell, showed the new mineral to be essentially a silicate of thorium and calcium, though about 2% of uranium was also present. A preliminary note was published in Nature on June 10th, 1961, establishing the new mineral at last, and appropriately honoring its discoverer in the name Ekanite. R K Mitchell gave an excellent account of the long drawn out investigation in the Journal of Gemmology, and shortly afterwards Dr Edward Gubelin who, unknown to us, had been working intensively on the new mineral, of which he had acquired no fewer than 12 specimens, published a long and brilliant paper on the subject in Gems and Gemology, The Gemmologist, and elsewhere, which precluded the need for any further work on our part.
Since that time, crystallized forms of ekanite have been reported from Central Asia by Russian workers and from Saint-Hilaire, Quebec Province, in pegmatite veins. The crystals are tetragonal. The reason for these not having been reduced to the metamict stage lies in their much younger geological age—60 million years against 600 million.
One thing that took away much of the pleasure from these investigations into new gem minerals was the long delay between the initial burst of ordinary gemological work on the stones and the final necessary chemical analysis and crystal structure analysis which had to be performed before the mineral could be properly established and the conclusions published a scientific paper. One could not very well press for speed from the skilled Museum workers, for work which involved a great deal of time and effort, which had to be added to their own research programmes and routine work for the department. And we ourselves in the laboratory found it increasingly hard to find time to work continuously on any project as the demands of essential daily testing work became more and more pressing. Visits to the library became lunch-time snatches, and one felt guilty in doing any work which could be termed purely academic. And most of you know how hard it is to pick up the threads of any piece of work which has been put on a shelf and allowed to grow cold.
Amongst the advantages of such pieces of research are the sharpening of technical skills, an increased international reputation for the laboratory and a closer liaison with mineralogists—a liaison which is vital in the present state of our science.
For those of you who have found my topic for this evening too remote from everyday experiences and problems in the trade to interest you, I can promise a thoroughly down-to-earth talk next October, when I understand that I am going to be allowed to speak to you again.
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