(via The Journal of Gemmology, Vol.XIV, No.3, July 1974) M J O’Donoghue writes:
In 1913 Dr O Dreher published a book entitled Farben des Achates, in Idar Oberstein. Long out-of-print, there is no copy in the library of the Gemmological Association nor in the British Museum. However, in his recent book, Gemstone & Mineral Data Book, John Sinkankas summarizes a number of Dr Dreher’s findings.
For obtaining a red color Dr Dreher recommends a dye solution with the following composition: ¼ kg iron nails dissolved in 1 kg concentrated nitric acid. When the liquid is clear the agate slabs are soaked for a duration depending on their thickness, e.g. 3 mm thick, 6 – 10 days, 7 – 10 mm from 3 – 4 weeks. Stones are then heated in a closed crucible for 2 – 3 or 8 – 10 days again according to the original thickness. Dreher found the iron nitrate supplied by a chemical house less satisfactory than the somewhat cumbersome nail method. S. Hoffman worked through the same method to obtain red agate.
For blue Dreher used 250 g of yellow potassium ferrocyanide dissolved in 1 litre of lukewarm water. Stones were immersed for 8 – 14 days. They are then washed and subsequently placed in a lukewarm saturated solution of ferrous sulphate.
For black the stones are immersed in a solution composed of 375 g of sugar per litre in which they are soaked for 2 – 3 weeks, with the occasional addition of water to replace losses through evaporation. They are rinsed and dried and then placed in a bath of concentrated sulphuric acid. This is warmed for one hour until it is hot. The stones are soaked for 1 – 2 hours while the acid is brought close to boiling point (340ºC). They are carefully washed on removal. It was not necessary to bring the acid to boiling point to achieve carbonization of the sugar.
Green staining is accomplished by the use of a saturated solution of chromium trioxide in 1 litre of water. Immersion lasts from 8 – 14 days for thin slabs, 2 – 8 weeks for thickness of 3 – 10 mm. After removal and rinsing the agates are placed in ammonium carbamate acid carbonate followed by heating to redness.
Tuesday, July 10, 2007
For Gemology Students
Prof Hermann Bank is one the most well known gemologist in the world. He shares the very lessons he had learnt during the past several decades as a teacher and researcher. All opportunities are accompanied by their own challenges. All the available knowledge in the world is accelerating at a phenomenal rate.
Prof Hermann Bank’s Address:
In his address, following the presentation of awards to the Gemmological Association of Great Britain at Goldsmith’s Hall on 14th November, 1983, including candidates from many different parts of the world, Prof Hermann Bank said:
Es war fur mich eine grosse Ehre, nach 7 Jahren wieder von der Gemmological Association of Great Britain eingeladen zu warden, um den erfolgreichen Kandidaten der Diplom-Prufugen des Jahres 1983 ihre Urkunden auszuhandigen. But as in 1976 I think that you would prefer that I try to continue in your language, and I beg you to excuse my poor English.
It was a great honor for me to be invited to present the awards of the Gemmological Association of Great Britain to the successful candidates of 1983, and I thank you very much for this invitation and the friendly welcome. The occasion is particularly pleasing for me for several reasons—(1) it is exactly 30 years since I passed the Diploma Examination in 1953 and became FGA; (2) as you have realized already, my eldest daughter is among you successful candidates; (3) it was pleasant to be able to present the Anderson-Bank Prize this year after Basic Anderson did it last year; (4) one must enjoy such an occasion anyhow. Since I have been asked to address you after having fulfilled my first task, I shall now try to fulfill my second too, and I should like especially to speak to the candidates.
You have now got your diplomas, and we hope that you do not think, as Goethe expressed in his Faust, ‘What you possess black on white you can confidently carry home,’ and relax on your success. It is one your duties to always perfect your gemological education, to keep your knowledge on a high standard, and you must allow me to give you some advice.
Gemology was much easier thirty years ago, and, if students of 1953 such a myself had remained on the level of knowledge of that time, they would now be lost. The developments and the progress have been so enormous in all fields of gemology that it has been necessary for us to learn steadily to keep always up to date.
There have been discovered new minerals. There have been found old minerals worth cutting. There have been invented new synthetic and artificial products. There have been effected new color manipulations, so many irradiations and diffusions and heatings, that it has also been necessary to use new techniques to disclose all these phenomena. Often the techniques must be more and more scientific to get the right results.
For a long time gemology was regarded only as a more commercial and technical appendix of mineralogy. The discovery of new mineral species by gemologists and the necessity of adoption of scientific methods to distinguish between gemstones and their substitutes or their manipulation have brought gemology to the level of a science. Last year the I M A (International Mineral Association) has formed its own commission on gem materials. That means, the I M A has accepted gemology on its own as scientific part of mineralogy. More and more mineralogists are taking an interest in gemological problems and assisting us to solve them, doing research on new minerals and varieties as well as on synthetic and imitation stones, their properties and distinguishing characteristics. Comprehensive information is increasingly important, and jeweler’s customers want more information. Therefore jewelers must have better education to be able to pass the required information on to their interested customers.
The Gemmological Association of Great Britain recognized this demand at the earliest stage and started gemological education courses over fifty years ago, and the courses have become an example and a model for gemological associations in other countries. The title FGA is highly esteemed throughout the world—hence the number of students every year. It is your proud duty to uphold the professional reputation which this title implies.
In the preliminary course the Gemmological Association of Great Britain tried to give the students a general idea, and, in the Diploma course, special theoretical knowledge and practical ability to use the various methods. However, we can only give and receive instruction until the day of the examination. Education combines the knowledge of the past with the unknown dark of the future by using wisely the present.
The candidates of today know—or at least should know—what we knew thirty years ago, and they also know what happened in these thirty years, but they and we do not know what problems will occur in the next thirty years. The unknown dark is spread over the developments of the future.
One fact is certain. New technologies will create new problems, and we can solve these problems only when we study steadily and try to keep on the newest stand of knowledge of the theoretical part and of the practical know-how of the methods.
A poet once said: ‘We must demand the extraordinary from ourselves to be able to do the ordinary.’
This we should at least try to do. If you have the slightest doubt, do not hesitate to consult an experienced colleague. We have a German proverb: ‘Was fur einen vielzuviel, ist fur 2 ein Kinderspiel.’ (What one cannot do is child’s play for two).
Experts are not made in heaven, and it is better to ask than to make an error. ‘Student is, who wants to learn something: Fellow or journey-man is, who knows something: Master is, who devised or invented something.’
Always take enough time to test a stone; never be in a hurry. Take your time also to study the Journal of Gemmology and other sources of information, and try to think, as Goethe expressed it: ‘Do not say, ‘Tomorrow I will do this and that: Do it, and wait until tomorrow and say then ‘I did it,’ which means, ‘Never put off till tomorrow what you can do today.’ Mineralogical gemologists and mineralogists try always to find and to develop new scientific equipments and methods which are suitable for easily distinguishing between gemstones and their substitutes, if possible without destroying them (neither gemstones nor substitutes).
Do not think that you only need to know a bit. A little learning is a dang’rous thing; Drink deep, or taste not the Pierian spring.’ (Pope: Essay on Criticism, 216). That means that we should try to obtain a thorough and comprehensive, broadly based knowledge.
The old Chinese said: ‘What you hear, you easily forget; What you see, you keep better in mind; Only what you have touched and worked with, you keep forever.’
So, please, use your instruments and get practice. In over ninety-nine percent of cases you can identify a stone by means of our classical gemological instruments—the polariscope, the conoscope, the refractometer, the microscope, the spectroscope, the UV lamp, etc. Only in very few cases is it necessary to consult X-ray powder methods or X-ray fluorescence or even X-ray topography or Tomography, the microprobe, IR spectroscopy or other more scientific equipments. But they are absolutely necessary for basic research and for doubtful cases.
It is not enough to have knowledge, it is necessary to use it.
And it is not enough to be willing, you must also do it.
So do work to get acquainted with methods and with all gemstones and their substitutes. The more you gain practice for yourself, the more you become sure on the one side but the more you also understand the verity of the two words of Socrates: ‘Scio nescio’ (I know what I do not know)
But Goethe consoles us when he writes: ‘It is not important what do know; but that we always have the right idea at the right moment.’
And it also is not correct that you should only buy instruments and textbooks, because often the purchase of a book is mistaken for the appropriation of the contents. So buy, use and read.
Successful candidates, I congratulate you on your Diplomas and I welcome you among the Fellows of the Gemmological Association of Great Britain. I wish you every success in your gemological future.
It is not important that one or the other of you will become a famous gemologist, but it is important that each and every one of you does his or her duty so that your clients have confidence in gemology and gemologists. To merit this confidence, do not remain on your present level of knowledge; study carefully to keep always up to date. Then I hope that your gemological practice will be characterized by a minimum of errors, a maximum of perfect results, and an optimum of joy. I wish you all the best and what is generally necessary in human life—a bit of good luck. Thank you.
Prof Hermann Bank’s Address:
In his address, following the presentation of awards to the Gemmological Association of Great Britain at Goldsmith’s Hall on 14th November, 1983, including candidates from many different parts of the world, Prof Hermann Bank said:
Es war fur mich eine grosse Ehre, nach 7 Jahren wieder von der Gemmological Association of Great Britain eingeladen zu warden, um den erfolgreichen Kandidaten der Diplom-Prufugen des Jahres 1983 ihre Urkunden auszuhandigen. But as in 1976 I think that you would prefer that I try to continue in your language, and I beg you to excuse my poor English.
It was a great honor for me to be invited to present the awards of the Gemmological Association of Great Britain to the successful candidates of 1983, and I thank you very much for this invitation and the friendly welcome. The occasion is particularly pleasing for me for several reasons—(1) it is exactly 30 years since I passed the Diploma Examination in 1953 and became FGA; (2) as you have realized already, my eldest daughter is among you successful candidates; (3) it was pleasant to be able to present the Anderson-Bank Prize this year after Basic Anderson did it last year; (4) one must enjoy such an occasion anyhow. Since I have been asked to address you after having fulfilled my first task, I shall now try to fulfill my second too, and I should like especially to speak to the candidates.
You have now got your diplomas, and we hope that you do not think, as Goethe expressed in his Faust, ‘What you possess black on white you can confidently carry home,’ and relax on your success. It is one your duties to always perfect your gemological education, to keep your knowledge on a high standard, and you must allow me to give you some advice.
Gemology was much easier thirty years ago, and, if students of 1953 such a myself had remained on the level of knowledge of that time, they would now be lost. The developments and the progress have been so enormous in all fields of gemology that it has been necessary for us to learn steadily to keep always up to date.
There have been discovered new minerals. There have been found old minerals worth cutting. There have been invented new synthetic and artificial products. There have been effected new color manipulations, so many irradiations and diffusions and heatings, that it has also been necessary to use new techniques to disclose all these phenomena. Often the techniques must be more and more scientific to get the right results.
For a long time gemology was regarded only as a more commercial and technical appendix of mineralogy. The discovery of new mineral species by gemologists and the necessity of adoption of scientific methods to distinguish between gemstones and their substitutes or their manipulation have brought gemology to the level of a science. Last year the I M A (International Mineral Association) has formed its own commission on gem materials. That means, the I M A has accepted gemology on its own as scientific part of mineralogy. More and more mineralogists are taking an interest in gemological problems and assisting us to solve them, doing research on new minerals and varieties as well as on synthetic and imitation stones, their properties and distinguishing characteristics. Comprehensive information is increasingly important, and jeweler’s customers want more information. Therefore jewelers must have better education to be able to pass the required information on to their interested customers.
The Gemmological Association of Great Britain recognized this demand at the earliest stage and started gemological education courses over fifty years ago, and the courses have become an example and a model for gemological associations in other countries. The title FGA is highly esteemed throughout the world—hence the number of students every year. It is your proud duty to uphold the professional reputation which this title implies.
In the preliminary course the Gemmological Association of Great Britain tried to give the students a general idea, and, in the Diploma course, special theoretical knowledge and practical ability to use the various methods. However, we can only give and receive instruction until the day of the examination. Education combines the knowledge of the past with the unknown dark of the future by using wisely the present.
The candidates of today know—or at least should know—what we knew thirty years ago, and they also know what happened in these thirty years, but they and we do not know what problems will occur in the next thirty years. The unknown dark is spread over the developments of the future.
One fact is certain. New technologies will create new problems, and we can solve these problems only when we study steadily and try to keep on the newest stand of knowledge of the theoretical part and of the practical know-how of the methods.
A poet once said: ‘We must demand the extraordinary from ourselves to be able to do the ordinary.’
This we should at least try to do. If you have the slightest doubt, do not hesitate to consult an experienced colleague. We have a German proverb: ‘Was fur einen vielzuviel, ist fur 2 ein Kinderspiel.’ (What one cannot do is child’s play for two).
Experts are not made in heaven, and it is better to ask than to make an error. ‘Student is, who wants to learn something: Fellow or journey-man is, who knows something: Master is, who devised or invented something.’
Always take enough time to test a stone; never be in a hurry. Take your time also to study the Journal of Gemmology and other sources of information, and try to think, as Goethe expressed it: ‘Do not say, ‘Tomorrow I will do this and that: Do it, and wait until tomorrow and say then ‘I did it,’ which means, ‘Never put off till tomorrow what you can do today.’ Mineralogical gemologists and mineralogists try always to find and to develop new scientific equipments and methods which are suitable for easily distinguishing between gemstones and their substitutes, if possible without destroying them (neither gemstones nor substitutes).
Do not think that you only need to know a bit. A little learning is a dang’rous thing; Drink deep, or taste not the Pierian spring.’ (Pope: Essay on Criticism, 216). That means that we should try to obtain a thorough and comprehensive, broadly based knowledge.
The old Chinese said: ‘What you hear, you easily forget; What you see, you keep better in mind; Only what you have touched and worked with, you keep forever.’
So, please, use your instruments and get practice. In over ninety-nine percent of cases you can identify a stone by means of our classical gemological instruments—the polariscope, the conoscope, the refractometer, the microscope, the spectroscope, the UV lamp, etc. Only in very few cases is it necessary to consult X-ray powder methods or X-ray fluorescence or even X-ray topography or Tomography, the microprobe, IR spectroscopy or other more scientific equipments. But they are absolutely necessary for basic research and for doubtful cases.
It is not enough to have knowledge, it is necessary to use it.
And it is not enough to be willing, you must also do it.
So do work to get acquainted with methods and with all gemstones and their substitutes. The more you gain practice for yourself, the more you become sure on the one side but the more you also understand the verity of the two words of Socrates: ‘Scio nescio’ (I know what I do not know)
But Goethe consoles us when he writes: ‘It is not important what do know; but that we always have the right idea at the right moment.’
And it also is not correct that you should only buy instruments and textbooks, because often the purchase of a book is mistaken for the appropriation of the contents. So buy, use and read.
Successful candidates, I congratulate you on your Diplomas and I welcome you among the Fellows of the Gemmological Association of Great Britain. I wish you every success in your gemological future.
It is not important that one or the other of you will become a famous gemologist, but it is important that each and every one of you does his or her duty so that your clients have confidence in gemology and gemologists. To merit this confidence, do not remain on your present level of knowledge; study carefully to keep always up to date. Then I hope that your gemological practice will be characterized by a minimum of errors, a maximum of perfect results, and an optimum of joy. I wish you all the best and what is generally necessary in human life—a bit of good luck. Thank you.
Cassiterite
Chemistry: Tin oxide (tin stone).
Crystal system: Tetragonal; prismatic, capped by pyramids; often twinned (geniculate); massive and granular, botryoidal, reniform with radial fibrous structure.
Color: Transparent to translucent; reddish brown to black, colorless, yellow.
Hardness: 6 - 7
Cleavage: Indistinct: brittle; Fracture: uneven, conchoidal.
Specific gravity: 6.8 – 7.1
Refractive index: 1.997 – 2.093; Uniaxial positive; 0.096.
Luster: Vitreous to adamantine; greasy on fracture.
Dispersion: Very high.
Dichroism: Weak to moderate; yellowish, brownish.
Occurrence: Granite and alluvial, high temperature hydrothermal veins and pegmatites; Australia, Bolivia, Malaysia, Mexico, Namibia, England.
Notes:
Principal ore of Tin; collectors stone; may be confused with diamond, hematite, sphene, zircon; faceted and cabochons.
Crystal system: Tetragonal; prismatic, capped by pyramids; often twinned (geniculate); massive and granular, botryoidal, reniform with radial fibrous structure.
Color: Transparent to translucent; reddish brown to black, colorless, yellow.
Hardness: 6 - 7
Cleavage: Indistinct: brittle; Fracture: uneven, conchoidal.
Specific gravity: 6.8 – 7.1
Refractive index: 1.997 – 2.093; Uniaxial positive; 0.096.
Luster: Vitreous to adamantine; greasy on fracture.
Dispersion: Very high.
Dichroism: Weak to moderate; yellowish, brownish.
Occurrence: Granite and alluvial, high temperature hydrothermal veins and pegmatites; Australia, Bolivia, Malaysia, Mexico, Namibia, England.
Notes:
Principal ore of Tin; collectors stone; may be confused with diamond, hematite, sphene, zircon; faceted and cabochons.
Monday, July 09, 2007
Anything Else
Memorable quote (s) from the movie:
David Dobel (Woody Allen): Since the beginning of time people have been, you know, frightened and, and unhappy, and they're scared of death, and they're scared of getting old, and there's always been priests around, and shamans, and now shrinks, to tell 'em, "Look, I know you're frightened, but I can help you. Of course, it is going to cost you a few bucks...” But they can't help you, Falk, because life is what it is.
David Dobel (Woody Allen): Since the beginning of time people have been, you know, frightened and, and unhappy, and they're scared of death, and they're scared of getting old, and there's always been priests around, and shamans, and now shrinks, to tell 'em, "Look, I know you're frightened, but I can help you. Of course, it is going to cost you a few bucks...” But they can't help you, Falk, because life is what it is.
Brazilianite
Chemistry: Hydrous sodium aluminum phosphate.
Crystal system: Monoclinic; short prism; large spear-shaped.
Color: Transparent to translucent; colorless with striations; yellow/green, yellow, colorless (rare).
Hardness: 5.5
Cleavage: Perfect: 1 direction, parallel to pinacoid faces; Fracture: brittle, conchoidal.
Specific gravity: 2.98
Refractive index: 1.603 – 1.623; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak (merely a change in shade).
Occurrence: Hydrothermal in pegmatite cavities. Brazil, U.S.A.
Notes
Collector's stone; heat sensitive; first found in 1944; may look like beryl, chrysoberyl, topaz, but R.I and DR different.
Crystal system: Monoclinic; short prism; large spear-shaped.
Color: Transparent to translucent; colorless with striations; yellow/green, yellow, colorless (rare).
Hardness: 5.5
Cleavage: Perfect: 1 direction, parallel to pinacoid faces; Fracture: brittle, conchoidal.
Specific gravity: 2.98
Refractive index: 1.603 – 1.623; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak (merely a change in shade).
Occurrence: Hydrothermal in pegmatite cavities. Brazil, U.S.A.
Notes
Collector's stone; heat sensitive; first found in 1944; may look like beryl, chrysoberyl, topaz, but R.I and DR different.
Brazilianite
Chemistry: Hydrous sodium aluminum phosphate.
Crystal system: Monoclinic; short prism; large spear-shaped.
Color: Transparent to translucent; colorless with striations; yellow/green, yellow, colorless (rare).
Hardness: 5.5
Cleavage: Perfect: 1 direction, parallel to pinacoid faces; Fracture: brittle, conchoidal.
Specific gravity: 2.98
Refractive index: 1.603 – 1.623; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak (merely a change in shade).
Occurrence: Hydrothermal in pegmatite cavities. Brazil, U.S.A.
Notes
Collector's stone; heat sensitive; first found in 1944; may look like beryl, chrysoberyl, topaz, but R.I and DR different.
Crystal system: Monoclinic; short prism; large spear-shaped.
Color: Transparent to translucent; colorless with striations; yellow/green, yellow, colorless (rare).
Hardness: 5.5
Cleavage: Perfect: 1 direction, parallel to pinacoid faces; Fracture: brittle, conchoidal.
Specific gravity: 2.98
Refractive index: 1.603 – 1.623; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak (merely a change in shade).
Occurrence: Hydrothermal in pegmatite cavities. Brazil, U.S.A.
Notes
Collector's stone; heat sensitive; first found in 1944; may look like beryl, chrysoberyl, topaz, but R.I and DR different.
Code of Practice Favoring Cultured Ambiguity
Chaim Even-Zohar writes about The Council for Responsible Jewellery Practices (CRJP) + its Code of Practices + gaps and shortcomings + other viewpoints @ http://www.idexonline.com/portal_FullEditorial.asp?TextSearch=&KeyMatch=0&id=26245
Sapphire Mining In Chantaburi (Thailand)
2007: Chantaburi has changed a lot since 1973. There are new types of colored stones coming from Africa, South Asia, and Southeast Asia + good quality rubies and sapphires are getting more difficult to find + foreign tourists, dealers, students are still visiting Chantaburi looking for the best deal and making mistakes.
(via The Journal of Gemmology, Vol.13, No.8, October 1973) J A L Pavitt writes:
Thailand, or Siam as it was formerly named, is a well-known source of sapphire, ruby, star-sapphire and zircon and over the years the skill of Thai lapidaries has advanced to a very high degree, making Bangkok, the capital city, an important center for the supply of cut gemstones.
There are a number of gem mining localities in Thailand, many of them in remote areas, but the mines at Chantaburi (also known as Chantabun), 200 miles from Bangkok, can be reached by car in five and a half hours, and soon after our arrival in Thailand in 1971 my wife and I made our first visit to Khau Ploi Waen, or ‘Hill of the Sapphire Ring’, as this mining area at Chantaburi is named. I have since made further visits, the most recent in January 1973 with Mr Kenneth Parkinson during his two week visit to Thailand.
Chantaburi has a very special place in the history and culture of the Kingdom of Thailand. Situated near the coast, only thirty miles from the border with Cambodia, its inhabitants, although loyal and proud Thai nationals have ethnic origins connecting many of them with the diverse civilizations which existed thousands of years ago between the borders of China and the Mekong Delta. These origins are still evident in the customs, skills, religious and dialects to be found among the people of this fertile eastern region of the Kingdom.
It was at Chantaburi that King Taksin marshaled his forces after the fall of the ancient city of Ayuthaya, and finally defeated and drove out the Burmese invaders. Close to the sapphire mines one can see the rusting cannon and remains of the fortress of King Rama III (1787 – 1851).
The gem-bearing deposits at Khau Ploi Waen are about six miles south of the town of Chantaburi, near the village of Ban Kacha. Past records indicate that in 1850 the Shans and Burmese were extracting sapphires here and that in 1850 a British Company obtained a lease but failed to make a success of the venture. In 1919 the Siam Mining Act came into force and since then mining has been solely in the hands of Thai nationals.
The mining area is privately owned and has been cleared of primary growth and planted with rubber trees, although it is obvious that an income from rubber tapping is of minor importance. A lease to dig for gemstones over an area of one ‘rai’ (approx. 0.4 acre) for one year is granted by the landlords for a fee which may be as high as baht 300000 for high yield areas which have not previously been worked. A lease is usually shared by groups or families and there are said to be some 2000 people mining around Khau Ploi Waen.
The method of extracting the stones is very primitive, as are the tools—a pick, a spade and a rattan basket. A vertical shaft of about four feet in diameter is dug in the red/brown clay soil, in between the rubber trees. These vertical shafts sometimes go as far as thirty feet deep and each basketful of soil is lifted to the surface by a crude, but effective, crane arrangement consisting of two bamboo legs and a long bamboo derrick arm with a rope and basket at one end and a counterbalance of large stones tied to the other end.
When a gem-bearing stratum is reached each basketful of soil is placed to one side at the top of the shaft, to be washed and sorted. In some instances a horizontal shaft will be dug to follow the gem-bearing stratum, but as no wooden props or tunnel shores are used the length of these horizontal tunnels is limited by the courage and tenacity of the digger, not to mention his ability to breathe in the tomblike atmosphere. No ladders are provided in the vertical shaft, and entry and exit are effected by bracing the back and hands against one wall and the feet against the opposite side, at the same time exerting the body in a motion that would do credit to James Bond in tightest spot.
There is no natural supply of water for washing the extractions, so the miners pay for this to be brought from the nearby village by water-tank lorries. A small pond about ten feet in diameter and three feet deep is formed near the shaft and the baskets of soil are washed and broken up by members of the group sitting in the pond. As and when the gemstones are found, these are placed in small plastic bags around the perimeter of the pond.
This particular area produces a fair quantity of corundum, most of the crystals being in the form of repeated lamellar twinning. In this form some of the stones can be cut en cabochon to exhibit fine golden six-rayed stars on a dark brown to nearly black background, and on my visit I met Khun Saengroong, a local dealer and cutter, who had just bought a magnificent hexagonal lamellar crystal of star sapphire material weighing 1720 carats. This is of course a rare exception and the average size seldom exceeds 15 carats, and even then only very few of the stones will, when cut, show a well-centered star without the disfiguration of the prominent zone lines which are a feature of the stones from this mine.
The local ‘test’ for rough star sapphire material is to place a drop of water on the stone and to view it from an overhead single light source. In a suitable crystal the ‘star’ will show up clearly when the drop of water is placed in the right position. As it is to be expected, a very great proportion of these opaque corundum crystals show a very poor, or no, star-effect, and these fetch very low prices.
In quantity, the second main gem production of this area is green sapphire, followed by blue/green, yellow/green and more rarely fine blue and yellow sapphire. The hexagonal zoning is easily detected under the lens in a large majority of these stones.
Also associated with the corundum are pyrope garnet (R.I=1.745-1.750) and a fairly large quantity of opaque black stones which take a high polish and are sold both faceted and en cabochon as ‘Thai Jet’. Kenneth Parkinson took ten of these back to the U.K and has since written to tell me that seven of these have a S.G of between 4.1 and 4.2 and with a R.I just visible at the very end of the standard refractometer it seems fairly certain that they are black almandines. The other three stones proved to be black diopside (no star or cat’s eye) with a clear double refraction 1.68 – 1.71. Although this is slightly higher than the normal 1.67 – 1.70, Webster (Gems, 2nd Edition, page 264) notes that the R.I may rise when the material is so dark as to be virtually hedenbergite.
Many jewelers and gem dealers in Bangkok will inform their customers ‘These stones come from our own mine at Chantaburi’, but it is very doubtful whether any of them actually engage in mining themselves, as those who have taken a lease and employed people to dig for them have usually found that somehow their area seems to produce only low-grade stones. The best quality stones will find their way into the market, but not through the lease-holder. The local expression is ‘employ someone to dig and your stone will fly.’
Dealers and middlemen gather at a small group of wooden coffee shops at the fork of two roads leading into the mining area and it is here, in the late afternoon, that the miners bring their daily production for sale.
The existence of these sapphire mines and others in the area producing ruby and zircon, has created a flourishing cutting and setting center in the town of Chantaburi. The standard of work is high, and compared with western prices, cutting costs are very low. A skilled Thai lapidary will be paid about 20 pence for faceting and polishing a zircon of one carat. These low cutting costs have prompted many of the local dealers to import rough gem material for cutting in Thailand and eventual export to the major markets in Europe and the USA. When Kenneth Parkinson and I were in Chantaburi we were shown a parcel of fine blue sapphire crystals recently purchased in Australia. One could not help thinking of the expression ‘bringing coals to Newcastle’.
Although sapphire, ruby and zircon are the principal materials cut at Chantaburi, opal, emerald and other rough is imported for cutting. It is perhaps inevitable that half boules of synthetic corundum are to be seen in many of the gem cutting shops, and, although the majority of dealers will not offer synthetics as anything but what they are, one suspects that a few will be sorely tempted when selling to some of the gullible foreign tourists who are now starting to visit this area.
(via The Journal of Gemmology, Vol.13, No.8, October 1973) J A L Pavitt writes:
Thailand, or Siam as it was formerly named, is a well-known source of sapphire, ruby, star-sapphire and zircon and over the years the skill of Thai lapidaries has advanced to a very high degree, making Bangkok, the capital city, an important center for the supply of cut gemstones.
There are a number of gem mining localities in Thailand, many of them in remote areas, but the mines at Chantaburi (also known as Chantabun), 200 miles from Bangkok, can be reached by car in five and a half hours, and soon after our arrival in Thailand in 1971 my wife and I made our first visit to Khau Ploi Waen, or ‘Hill of the Sapphire Ring’, as this mining area at Chantaburi is named. I have since made further visits, the most recent in January 1973 with Mr Kenneth Parkinson during his two week visit to Thailand.
Chantaburi has a very special place in the history and culture of the Kingdom of Thailand. Situated near the coast, only thirty miles from the border with Cambodia, its inhabitants, although loyal and proud Thai nationals have ethnic origins connecting many of them with the diverse civilizations which existed thousands of years ago between the borders of China and the Mekong Delta. These origins are still evident in the customs, skills, religious and dialects to be found among the people of this fertile eastern region of the Kingdom.
It was at Chantaburi that King Taksin marshaled his forces after the fall of the ancient city of Ayuthaya, and finally defeated and drove out the Burmese invaders. Close to the sapphire mines one can see the rusting cannon and remains of the fortress of King Rama III (1787 – 1851).
The gem-bearing deposits at Khau Ploi Waen are about six miles south of the town of Chantaburi, near the village of Ban Kacha. Past records indicate that in 1850 the Shans and Burmese were extracting sapphires here and that in 1850 a British Company obtained a lease but failed to make a success of the venture. In 1919 the Siam Mining Act came into force and since then mining has been solely in the hands of Thai nationals.
The mining area is privately owned and has been cleared of primary growth and planted with rubber trees, although it is obvious that an income from rubber tapping is of minor importance. A lease to dig for gemstones over an area of one ‘rai’ (approx. 0.4 acre) for one year is granted by the landlords for a fee which may be as high as baht 300000 for high yield areas which have not previously been worked. A lease is usually shared by groups or families and there are said to be some 2000 people mining around Khau Ploi Waen.
The method of extracting the stones is very primitive, as are the tools—a pick, a spade and a rattan basket. A vertical shaft of about four feet in diameter is dug in the red/brown clay soil, in between the rubber trees. These vertical shafts sometimes go as far as thirty feet deep and each basketful of soil is lifted to the surface by a crude, but effective, crane arrangement consisting of two bamboo legs and a long bamboo derrick arm with a rope and basket at one end and a counterbalance of large stones tied to the other end.
When a gem-bearing stratum is reached each basketful of soil is placed to one side at the top of the shaft, to be washed and sorted. In some instances a horizontal shaft will be dug to follow the gem-bearing stratum, but as no wooden props or tunnel shores are used the length of these horizontal tunnels is limited by the courage and tenacity of the digger, not to mention his ability to breathe in the tomblike atmosphere. No ladders are provided in the vertical shaft, and entry and exit are effected by bracing the back and hands against one wall and the feet against the opposite side, at the same time exerting the body in a motion that would do credit to James Bond in tightest spot.
There is no natural supply of water for washing the extractions, so the miners pay for this to be brought from the nearby village by water-tank lorries. A small pond about ten feet in diameter and three feet deep is formed near the shaft and the baskets of soil are washed and broken up by members of the group sitting in the pond. As and when the gemstones are found, these are placed in small plastic bags around the perimeter of the pond.
This particular area produces a fair quantity of corundum, most of the crystals being in the form of repeated lamellar twinning. In this form some of the stones can be cut en cabochon to exhibit fine golden six-rayed stars on a dark brown to nearly black background, and on my visit I met Khun Saengroong, a local dealer and cutter, who had just bought a magnificent hexagonal lamellar crystal of star sapphire material weighing 1720 carats. This is of course a rare exception and the average size seldom exceeds 15 carats, and even then only very few of the stones will, when cut, show a well-centered star without the disfiguration of the prominent zone lines which are a feature of the stones from this mine.
The local ‘test’ for rough star sapphire material is to place a drop of water on the stone and to view it from an overhead single light source. In a suitable crystal the ‘star’ will show up clearly when the drop of water is placed in the right position. As it is to be expected, a very great proportion of these opaque corundum crystals show a very poor, or no, star-effect, and these fetch very low prices.
In quantity, the second main gem production of this area is green sapphire, followed by blue/green, yellow/green and more rarely fine blue and yellow sapphire. The hexagonal zoning is easily detected under the lens in a large majority of these stones.
Also associated with the corundum are pyrope garnet (R.I=1.745-1.750) and a fairly large quantity of opaque black stones which take a high polish and are sold both faceted and en cabochon as ‘Thai Jet’. Kenneth Parkinson took ten of these back to the U.K and has since written to tell me that seven of these have a S.G of between 4.1 and 4.2 and with a R.I just visible at the very end of the standard refractometer it seems fairly certain that they are black almandines. The other three stones proved to be black diopside (no star or cat’s eye) with a clear double refraction 1.68 – 1.71. Although this is slightly higher than the normal 1.67 – 1.70, Webster (Gems, 2nd Edition, page 264) notes that the R.I may rise when the material is so dark as to be virtually hedenbergite.
Many jewelers and gem dealers in Bangkok will inform their customers ‘These stones come from our own mine at Chantaburi’, but it is very doubtful whether any of them actually engage in mining themselves, as those who have taken a lease and employed people to dig for them have usually found that somehow their area seems to produce only low-grade stones. The best quality stones will find their way into the market, but not through the lease-holder. The local expression is ‘employ someone to dig and your stone will fly.’
Dealers and middlemen gather at a small group of wooden coffee shops at the fork of two roads leading into the mining area and it is here, in the late afternoon, that the miners bring their daily production for sale.
The existence of these sapphire mines and others in the area producing ruby and zircon, has created a flourishing cutting and setting center in the town of Chantaburi. The standard of work is high, and compared with western prices, cutting costs are very low. A skilled Thai lapidary will be paid about 20 pence for faceting and polishing a zircon of one carat. These low cutting costs have prompted many of the local dealers to import rough gem material for cutting in Thailand and eventual export to the major markets in Europe and the USA. When Kenneth Parkinson and I were in Chantaburi we were shown a parcel of fine blue sapphire crystals recently purchased in Australia. One could not help thinking of the expression ‘bringing coals to Newcastle’.
Although sapphire, ruby and zircon are the principal materials cut at Chantaburi, opal, emerald and other rough is imported for cutting. It is perhaps inevitable that half boules of synthetic corundum are to be seen in many of the gem cutting shops, and, although the majority of dealers will not offer synthetics as anything but what they are, one suspects that a few will be sorely tempted when selling to some of the gullible foreign tourists who are now starting to visit this area.
Subscribe to:
Posts (Atom)