(via Diamond Promotion Service) Diamond Cutting: 28. The beauty of a gem diamond depends on the way it handles light. Diamond cutting unlocks this beauty.
The ancient Indian lapidaries learned that the surfaces of a diamond could be polished by rubbing another diamond against them. This enabled the diamond to reflect more light, and in ancient times the diamond was called the Venus stone because of its brightness. In the 15th century important discoveries were made which resulted in even brighter stones through the grinding of additional facets or planes. More than two centuries later a Venetian cutter named Peruzzi invented the 58-facet form for round diamonds that is basic to today’s cutting. In 1919 Marcel Tolkowsky, a physicist, developed the relationship of facet angles that is considered ideal for modern cutting.
Antwerp and Israel are the largest diamond cutting centers in the world. Other important centers are Amsterdam, United States, India, West Germany and South Africa. Cutting is also done on a lesser scale in England, Puerto Rico, Russia, France and Portugal. Each center has gradually, over the years, come to specialize in cutting a particular quality of diamonds. Cleavages and chips are, in the main, worked in Antwerp; stones and shapes in the United States; and melee in Amsterdam, Israel and West Germany.
29. Marking. The first step in diamond cutting is an examination of the rough stone by the planner, usually a master cutter. Using his loupe, or magnifying glass, he studies every aspect of the stone. For very large diamonds, this study can go on for months, but for the average diamond the study is done in a few minutes. Nevertheless, every diamond must be studied, no matter how small it is.
The planner has to be conscious of two factors. Under normal circumstances, a rough diamond loses more than half its weight in the cutting process; so the planner has to determine the finished shape that will retain as much weight as possible. Most diamonds contain natural imperfections, or inclusions; so that planner has to position the finished shape and direct the cutting so that as many inclusions as possible can be ground away and the remaining inclusions will offer minimum interference with the passage of light through the stone. Sometimes, to eliminate a major inclusion, the planner will have a stone cut smaller than it could be.
Then he marks the diamond with India ink to indicate how the cutting will go. The principal mark shows how the stone must be divided. An octahedron crystal is usually divided just above the middle, and both parts are cut into round diamonds. An irregular piece of rough may be divided into several pieces, and each piece will be cut into a finished gem. When a piece of rough is already close to the shape of a finished gem, it may not be divided at all but just ground down into the finished shape.
30. Sawing. Most octahdedron crystals, and many irregular shapes, are divided ‘against the grain’, and so they are sawed. Only diamond will cut diamond; therefore, the saw is a thin disk of phosphor bronze, its edge coated with a paste of oil and diamond dust. The saw is mounted vertically and spins at high speed. The diamond is set into a clamp so that it can be lowered against the saw’s edge in the plane along which it must be divided. Gravity keeps the stone against the saw while it is being cut.
It takes hours to cut through even a small diamond. However, one sawyer can handle a batter of saws, checking each stone at intervals to ensure that is being sawed correctly. The deviation of even a hair can affect the finished gem.
Selling Diamonds (continued)
Thursday, October 04, 2007
Wednesday, October 03, 2007
Bangkok Gems And Jewelry Fair
According to Vichai Assarasakorn, chief executive of the BGJF organizing committee, the show went beyond expectation in the wake of adverse impacts like the sluggish global economy and, more recently, the U.S. sub-prime loan fallout + more than 10 national groups from such markets as Europe, India, Russia and the United States met with exhibitors at the fair.
According to Thailand's Minister of Commerce Krik-krai Jirapaet, gems and jewelry exports last year exceeded $3.6 billion, up 12.7 percent from the previous year. In the first seven months of this year, gems and jewelry exports increased 5.41 percent year-on-year to $2.18 billion.
The next edition of the Bangkok Gems and Jewelry Fair will take place from Feb. 27-March 2, 2008.
According to Thailand's Minister of Commerce Krik-krai Jirapaet, gems and jewelry exports last year exceeded $3.6 billion, up 12.7 percent from the previous year. In the first seven months of this year, gems and jewelry exports increased 5.41 percent year-on-year to $2.18 billion.
The next edition of the Bangkok Gems and Jewelry Fair will take place from Feb. 27-March 2, 2008.
When's The Best Time To Buy Gold?
Moneyweek writes about the tight supply and growing demand of gold + the market trends + other viewpoints @ http://www.moneyweek.com/file/12405/whens-the-best-time-to-buy-gold.html
The Top 50
The Guardian profiles UK's brightest/biggest designers + their concepts @ http://arts.guardian.co.uk/art/design/story/0,,2159165,00.html
The Istanbul Biennial
Peter Schjeldahl writes about The Istanbul Biennial, one of the first non-Western biennials, and one of only a few in Muslim countries + its fun-filled, earnest concepts + other viewpoints @ http://www.newyorker.com/arts/critics/artworld/2007/10/08/071008craw_artworld_schjeldahl
About The Turner Prize
(via The Guardian) Jonathan Jones writes about the Turner prize + other viewpoints @ http://arts.guardian.co.uk/art/news/story/0,,2181514,00.html
Useful links:
Turner prize 2007
In pictures: the shortlisted artists
About Mark Wallinger
Adrian Searle on Mark Wallinger's State Britain
What do you think of State Britain?
State Britain in pictures
Adrian Searle on Wallinger's Trafalgar Square sculpture
Mark Wallinger's 1995 Turner prize entry
About Zarina Bhimji
Adrian Searle reviews Documenta
Yasmin Alibhai-Brown on Muslim artists in Britain
Zarina Bhimji official site
Haunchofvenison.com: biography of Bhimji
About Nathan Coley
Adrian Searle on 2005's macabre summer shows
Doggerfisher.com: see works by Nathan Coley
About Mike Nelson
News: Art on drugs in Margate
Jonathan Jones talks to Mike Nelson
Mike Nelson's 2001 Turner prize entry
Tate: Mike Nelson profile
Mike Nelson at Frieze Art Fair
Special report
Full coverage: Turner prize 2006
Useful links:
Turner prize 2007
In pictures: the shortlisted artists
About Mark Wallinger
Adrian Searle on Mark Wallinger's State Britain
What do you think of State Britain?
State Britain in pictures
Adrian Searle on Wallinger's Trafalgar Square sculpture
Mark Wallinger's 1995 Turner prize entry
About Zarina Bhimji
Adrian Searle reviews Documenta
Yasmin Alibhai-Brown on Muslim artists in Britain
Zarina Bhimji official site
Haunchofvenison.com: biography of Bhimji
About Nathan Coley
Adrian Searle on 2005's macabre summer shows
Doggerfisher.com: see works by Nathan Coley
About Mike Nelson
News: Art on drugs in Margate
Jonathan Jones talks to Mike Nelson
Mike Nelson's 2001 Turner prize entry
Tate: Mike Nelson profile
Mike Nelson at Frieze Art Fair
Special report
Full coverage: Turner prize 2006
Orthodox Bulldozer
Konstantin Akinsha writes about the background of rising nationalism and Orthodox assertiveness by Russian Orthodox activists + the influential members of the congregation of St. Nicholas in Pyzhi (whose archpriest, Alexander Shargunov, is a well-known radical fundamentalist) + the Sakharov Museum controversy + other viewpoints @ http://artnews.com/issues/article.asp?art_id=1521
Selling Diamonds
(via Diamond Promotion Service) 21. The diamonds are separated from the concentrate in the final steps of recovery. Until recently, this was done primarily by grease tables or grease belts. Diamonds are water-resistant; therefore when the concentrate is sluiced over tables or moving belts coated with a heavy grease, the diamonds stick to the grease and the rest of the material is washed away. Then the diamonds and grease are scraped up and put into boiling water which cleans away the grease.
22. The latest development for this final recovery is X-ray separation. A diamond fluoresces in an X-ray beam. The diamondiferous concentrate passes a beam. The fluorescence triggers a photoelectric cell, which in turn, trips a jet of air that blows the diamond out of the main stream. When another mineral passes the electronic eye, nothing happens. This method of separation is incredibly fast, and it’s more than 99 percent effective.
23. In alluvial mines, the diamonds are usually found among the gravels and other material lying on the bedrock. The sand or earthen overburden is scraped up and dumped in an other location. Then the diamond-bearing gravels are scooped up and taken away for the recovery treatment. Every crevice of the bedrock is swept clean with brooms to make sure that they get all the diamonds. The recovery process is essentially the same as for ore from the open cast and underground mines.
24. The ratio of diamonds within the diamond-bearing rock is very low. In some mines, to recover one ounce of diamonds—which is 142 carats—the miners have to dig as much as 112,000,000 ounces of material—which is 3500 tons. Furthermore, the average size of the rough diamonds is less than a carat. So in one ounce of rough—142 carats—there may be only half a dozen stones larger than a carat, and a couple of hundred smaller than half a carat.
25. Of the total world production of rough diamonds, only about 20 percent are capable of being cut into gem diamonds. The rest are put to industrial use for the cutting, grinding and polishing of a great variety of materials used in manufacturing. The gem-industrial ratio varies from country to country. Production in the Republic of Zaire (DR Congo) runs more than 98 percent industrial while that of South-West Africa is more than 90 percent gem.
26. Broadly, diamonds are sorted in the following categories: stones, which are octahedral in shape and look like two four-sided pyramids joined at their bases; cleavages, or broken and blocky pieces; macles, which are triangular stones usually with a herring-bone line around them; and flats, or thin but cuttable diamonds. Stones and shapes weighing less than one carat in the rough are known as melee. Cleavages under one carat in the rough are known as chips. Bort, ballas and carbonado are varieties of diamond used only in industry.
27. Synthetic diamonds for industrial uses are being manufactured by subjecting graphite compounds to tremendous heat and pressure in giant presses. Synthetic gem diamonds have been made in laboratory experiments, but only at great cost, far more than the cost of natural gem diamonds.
Selling Diamonds (continued)
22. The latest development for this final recovery is X-ray separation. A diamond fluoresces in an X-ray beam. The diamondiferous concentrate passes a beam. The fluorescence triggers a photoelectric cell, which in turn, trips a jet of air that blows the diamond out of the main stream. When another mineral passes the electronic eye, nothing happens. This method of separation is incredibly fast, and it’s more than 99 percent effective.
23. In alluvial mines, the diamonds are usually found among the gravels and other material lying on the bedrock. The sand or earthen overburden is scraped up and dumped in an other location. Then the diamond-bearing gravels are scooped up and taken away for the recovery treatment. Every crevice of the bedrock is swept clean with brooms to make sure that they get all the diamonds. The recovery process is essentially the same as for ore from the open cast and underground mines.
24. The ratio of diamonds within the diamond-bearing rock is very low. In some mines, to recover one ounce of diamonds—which is 142 carats—the miners have to dig as much as 112,000,000 ounces of material—which is 3500 tons. Furthermore, the average size of the rough diamonds is less than a carat. So in one ounce of rough—142 carats—there may be only half a dozen stones larger than a carat, and a couple of hundred smaller than half a carat.
25. Of the total world production of rough diamonds, only about 20 percent are capable of being cut into gem diamonds. The rest are put to industrial use for the cutting, grinding and polishing of a great variety of materials used in manufacturing. The gem-industrial ratio varies from country to country. Production in the Republic of Zaire (DR Congo) runs more than 98 percent industrial while that of South-West Africa is more than 90 percent gem.
26. Broadly, diamonds are sorted in the following categories: stones, which are octahedral in shape and look like two four-sided pyramids joined at their bases; cleavages, or broken and blocky pieces; macles, which are triangular stones usually with a herring-bone line around them; and flats, or thin but cuttable diamonds. Stones and shapes weighing less than one carat in the rough are known as melee. Cleavages under one carat in the rough are known as chips. Bort, ballas and carbonado are varieties of diamond used only in industry.
27. Synthetic diamonds for industrial uses are being manufactured by subjecting graphite compounds to tremendous heat and pressure in giant presses. Synthetic gem diamonds have been made in laboratory experiments, but only at great cost, far more than the cost of natural gem diamonds.
Selling Diamonds (continued)
Tuesday, October 02, 2007
How Green Was My Valley
Greatest Opening Film Lines (How Green Was My Valley - 1941):
I am packing my belongings in the shawl my mother used to wear when she went to the market. And I'm going from my valley. And this time, I shall never return. I am leaving behind me my fifty years of memory. Memory. Streams that the mind will forget so much of what only this moment has passed, and yet hold clear and bright the memory of what happened years ago - of men and women long since dead.
I liked this one.
I am packing my belongings in the shawl my mother used to wear when she went to the market. And I'm going from my valley. And this time, I shall never return. I am leaving behind me my fifty years of memory. Memory. Streams that the mind will forget so much of what only this moment has passed, and yet hold clear and bright the memory of what happened years ago - of men and women long since dead.
I liked this one.
Common Gemstone Treatments
A number of gem materials are treated to alter their appearance. Temperatures may vary considerably depending on the material and the desired effect. In some cases relatively low temperatures may cause the desired change (s).
Amber may be heated to produce a number of desired changes. Most commonly it is heated to induce discoid fractures known as ‘sun spangles’ that some consider desirable. It may also be heated to change yellow material to a darker, more orange brown color, thereby resembling naturally age-oxidized material. Cloudy amber containing a myriad of tiny gas bubbles may be clarified by heating, usually while immersed in an oil medium (rapeseed or linseed oil). The presence of sun spangles is generally assumed to imply treatment whereas the heat oxidation and clarification processes are not normally detectable.
Aquamarine, a beryl variety, most commonly occurs in nature as a blue-green stone, the color from which it derives its name (meaning seawater). Today, however, a purer blue is more marketable. Heat treatment is therefore used to remove the yellow component of its color, leaving the stable blue. The same treatment is used to remove the yellow component from some peachy morganite beryl, resulting in a purer pink color. Because of the relatively low temperatures used, heat treated aquamarine and morganite rarely show the type of heat-treated damage used to determine heat treatment in some corundum, so detection is generally not possible.
One of the commercially more significant varieties of quartz is amethyst. The stone is heated to improve the color of dark-toned material by bleaching out some of the purple color and/or removing a smoky component. In both cases the heating (partially or completely) reverses radiation-induced structural damage that produced color centers. Heating to high temperatures is routinely used on amethyst from some sources to produce the yellow quartz variety, citrine. It is believed that practically all of the citrine on the market today is the result of such treatments. Some amethyst, upon heating, will convert to citrine in some zones and not others; this results in the bi-colored amethyst-citrine variety that has marketed under the trade name Ametrine.
Some brown to orange topaz owes its color to a combination of a chromium-produced pink component and color-center-produced yellow-to-brown component. Heating such materials repairs the structural damage that produces the yellowish component, leaving only the stable pink color. This process, which requires relatively low temperatures, is referred to as ‘pinking’. The material reportedly shows stronger dichroism than untreated natural pink topaz. Heating is also a step in the production of some irradiated blue topaz, as some irradiation sources will produce color centers for both blue and yellow to brown colors. The heating removes the yellowish component, leaving the more stable blue color.
Amber may be heated to produce a number of desired changes. Most commonly it is heated to induce discoid fractures known as ‘sun spangles’ that some consider desirable. It may also be heated to change yellow material to a darker, more orange brown color, thereby resembling naturally age-oxidized material. Cloudy amber containing a myriad of tiny gas bubbles may be clarified by heating, usually while immersed in an oil medium (rapeseed or linseed oil). The presence of sun spangles is generally assumed to imply treatment whereas the heat oxidation and clarification processes are not normally detectable.
Aquamarine, a beryl variety, most commonly occurs in nature as a blue-green stone, the color from which it derives its name (meaning seawater). Today, however, a purer blue is more marketable. Heat treatment is therefore used to remove the yellow component of its color, leaving the stable blue. The same treatment is used to remove the yellow component from some peachy morganite beryl, resulting in a purer pink color. Because of the relatively low temperatures used, heat treated aquamarine and morganite rarely show the type of heat-treated damage used to determine heat treatment in some corundum, so detection is generally not possible.
One of the commercially more significant varieties of quartz is amethyst. The stone is heated to improve the color of dark-toned material by bleaching out some of the purple color and/or removing a smoky component. In both cases the heating (partially or completely) reverses radiation-induced structural damage that produced color centers. Heating to high temperatures is routinely used on amethyst from some sources to produce the yellow quartz variety, citrine. It is believed that practically all of the citrine on the market today is the result of such treatments. Some amethyst, upon heating, will convert to citrine in some zones and not others; this results in the bi-colored amethyst-citrine variety that has marketed under the trade name Ametrine.
Some brown to orange topaz owes its color to a combination of a chromium-produced pink component and color-center-produced yellow-to-brown component. Heating such materials repairs the structural damage that produces the yellowish component, leaving only the stable pink color. This process, which requires relatively low temperatures, is referred to as ‘pinking’. The material reportedly shows stronger dichroism than untreated natural pink topaz. Heating is also a step in the production of some irradiated blue topaz, as some irradiation sources will produce color centers for both blue and yellow to brown colors. The heating removes the yellowish component, leaving the more stable blue color.
Designers' London
(via The Observer) It's all about top designers and their inspirations + the places and spaces in London that motivates them most + other viewpoints @ http://arts.guardian.co.uk/art/design/story/0,,2162272,00.html
Damien Hirst Speaks
(via The Guardian) I really liked Damien Hirst's artwork because it inspiring + the way he connects the dots is remarkable.
Useful links:
http://arts.guardian.co.uk/art/visualart/story/0,,2180929,00.html
Damien Hirst: Beyond Belief
On the blog
Jonathan Jones: Buy the skull for the nation
Related articles
06.06.2007: Jonathan Glancey: Now you, too, can own a version of Damien's £50m skull
04.06.2007: Who would pay £50m for Hirst's skull?
02.06.2007: Diamonds are a skull's best friend
25.10.2006: Jonathan Jones: Fresh out of ideas
20.06.2006: Charlotte Higgins meets maverick British artist Damien Hirst
24.10.2005: The bell tolls for Hirst's tried and tested work
01.09.2005: Hirst snaps up rotting Gothic manor
13.06.2005: Hirst ditches plans to use photograph from scene of unsolved murder
07.04.2005: Hirst show 'terrible', say New York critics
04.03.2005: Damien Hirst, Gagosian, London
28.01.2005: Eternal city finds holy site for Hirst
16.01.2005: Hirst shark sold for £7m
27.11.2003: Hirst buys his art back from Saatchi
The Hirst Files
06.10.2001: Part 1: Student works, butterflies and corpses
06.10.2001: Part 2: Lost weekends, Charles Saatchi and Pharmacy
07.10.2001: Part 3: Rows with Matthew Freud, his comeback, and how to buy a very big fish
25.10.2006: Jonathan Jones: Fresh out of ideas
Useful links:
http://arts.guardian.co.uk/art/visualart/story/0,,2180929,00.html
Damien Hirst: Beyond Belief
On the blog
Jonathan Jones: Buy the skull for the nation
Related articles
06.06.2007: Jonathan Glancey: Now you, too, can own a version of Damien's £50m skull
04.06.2007: Who would pay £50m for Hirst's skull?
02.06.2007: Diamonds are a skull's best friend
25.10.2006: Jonathan Jones: Fresh out of ideas
20.06.2006: Charlotte Higgins meets maverick British artist Damien Hirst
24.10.2005: The bell tolls for Hirst's tried and tested work
01.09.2005: Hirst snaps up rotting Gothic manor
13.06.2005: Hirst ditches plans to use photograph from scene of unsolved murder
07.04.2005: Hirst show 'terrible', say New York critics
04.03.2005: Damien Hirst, Gagosian, London
28.01.2005: Eternal city finds holy site for Hirst
16.01.2005: Hirst shark sold for £7m
27.11.2003: Hirst buys his art back from Saatchi
The Hirst Files
06.10.2001: Part 1: Student works, butterflies and corpses
06.10.2001: Part 2: Lost weekends, Charles Saatchi and Pharmacy
07.10.2001: Part 3: Rows with Matthew Freud, his comeback, and how to buy a very big fish
25.10.2006: Jonathan Jones: Fresh out of ideas
Hanging On
(via The Guardian) In my view, provided proper safeguards were in place museums and galleries should be free to sell off works of art and other objects from their collections.
Useful link:
http://arts.guardian.co.uk/art/visualart/story/0,,2179460,00.html
Useful link:
http://arts.guardian.co.uk/art/visualart/story/0,,2179460,00.html
The 10 Most Expensive Living Artists
Kelly Devine Thomas profiles the most expensive living artists @ http://artnews.com/issues/article.asp?art_id=1520
Selling Diamonds
(via Diamond Promotion Service) Diamond Mining: 15. It is believed that diamonds were formed by heat and pressure, millions of years ago, deep within the earth. Later, the magma in which the diamonds were embedded was forced to the surface through fissures like the throats of ancients volcanoes. This material then cooled into formations that we call ‘pipes’. Diamond pipes are being mined today in Botswana, Siberia, South Africa and Tanzania.
16. However, all these formations did not remain intact. Exposed to rain and heat cold for millions of years, many diamond-bearing pipes weathered away. Because the diamonds were so hard, they didn’t break up like the other material. Rather, they were carried along by streams and rivers. When their size or specific gravity was too much for the force of the water, they dropped to the river beds. These are called alluvial deposits, and most of the world’s diamonds come from alluvial mining. The pipe mine in Botswana was discovered by geologists who backtracked from an alluvial deposit along the course of an ancient river.
17. In certain areas of southern Africa, it is believed that some rivers carried diamonds all the way to the Atlantic Ocean, where wave wash deposited them in marine terraces. Some of these terraces are now on dry land, where they are being mined. There is another theory that the diamonds were washed up on the beaches from volcanic pipes on the ocean floor.
18. A diamond pipe is usually composed of a rock-like material called kimberlite, or blue ground. When a diamond pipe is mined, the first step is to dig into it from the surface, like the excavation for a huge building. This is called open-cast mining. It can continue until the hole is too deep for the ore to be brought to the surface easily, but this depth can be 800 to 1000 feet. The Finsch Mine in South Africa, the Williamson Mine in Tanzania and the Orapa Mine in Botswana are open cast mines.
19. When the hole gets too deep, the mine goes underground. Vertical shafts are sunk into the ‘country rock’ away from the pipe. Although there are different methods for underground mining, the basic technique is to drive horizontal tunnels from the shafts into the pipe and then to dig out the diamond-bearing ore from below. This, of course, makes the hole deeper, and the tunnels are driven at successively lower levels until the entire pipe has been mined out, leaving only a hole where the pipe had been. The Big Hole at Kimberley, now the site of a diamond museum, is what remains after the Kimberley Mine was mined out in 1914; now filling with water, it is 1335 feet deep, one of the deepest man-made holes on earth.
20. After the diamond-bearing ore is brought to the surface from either open cast or underground mine, it is put through a long and complex recovery process. The ore is broken up in mills that exert enough force to break the kimberlite, but not the diamonds it contains. Then the broken ore goes through a series of washings, jiggings and screenings that remove much of the waste material. Then what’s left is put into huge tanks that look like mud puddles; the liquid is heavier than water, however, so that the diamonds and other heavier minerals can sink to the bottom in a concentrate while the lighter waste material floats off.
Selling Diamonds (continued)
16. However, all these formations did not remain intact. Exposed to rain and heat cold for millions of years, many diamond-bearing pipes weathered away. Because the diamonds were so hard, they didn’t break up like the other material. Rather, they were carried along by streams and rivers. When their size or specific gravity was too much for the force of the water, they dropped to the river beds. These are called alluvial deposits, and most of the world’s diamonds come from alluvial mining. The pipe mine in Botswana was discovered by geologists who backtracked from an alluvial deposit along the course of an ancient river.
17. In certain areas of southern Africa, it is believed that some rivers carried diamonds all the way to the Atlantic Ocean, where wave wash deposited them in marine terraces. Some of these terraces are now on dry land, where they are being mined. There is another theory that the diamonds were washed up on the beaches from volcanic pipes on the ocean floor.
18. A diamond pipe is usually composed of a rock-like material called kimberlite, or blue ground. When a diamond pipe is mined, the first step is to dig into it from the surface, like the excavation for a huge building. This is called open-cast mining. It can continue until the hole is too deep for the ore to be brought to the surface easily, but this depth can be 800 to 1000 feet. The Finsch Mine in South Africa, the Williamson Mine in Tanzania and the Orapa Mine in Botswana are open cast mines.
19. When the hole gets too deep, the mine goes underground. Vertical shafts are sunk into the ‘country rock’ away from the pipe. Although there are different methods for underground mining, the basic technique is to drive horizontal tunnels from the shafts into the pipe and then to dig out the diamond-bearing ore from below. This, of course, makes the hole deeper, and the tunnels are driven at successively lower levels until the entire pipe has been mined out, leaving only a hole where the pipe had been. The Big Hole at Kimberley, now the site of a diamond museum, is what remains after the Kimberley Mine was mined out in 1914; now filling with water, it is 1335 feet deep, one of the deepest man-made holes on earth.
20. After the diamond-bearing ore is brought to the surface from either open cast or underground mine, it is put through a long and complex recovery process. The ore is broken up in mills that exert enough force to break the kimberlite, but not the diamonds it contains. Then the broken ore goes through a series of washings, jiggings and screenings that remove much of the waste material. Then what’s left is put into huge tanks that look like mud puddles; the liquid is heavier than water, however, so that the diamonds and other heavier minerals can sink to the bottom in a concentrate while the lighter waste material floats off.
Selling Diamonds (continued)
Monday, October 01, 2007
Different Types Of Star Gemstones
In general, star gemstones occur in fewer minerals. In theory, if right conditions were present, almost any mineral could produce asterism.
In a star ruby or sapphire, titanium oxide is exsolved as fine needles of rutile. They orient themselves in three directions, intersecting at 60° and 120° within the same plane producing beautiful stars. The most desirable black star sapphires are those which exhibit the golden star and can be many times more valuable than the more common white-rayed black star sapphires. The asterism of black star sapphire is due to perfectly oriented intergrowth of elongated hematite lamellae. Asterism can be produced in certain types of non-asteriated corundum by moderate heating, if a piece of natural corundum contains enough titanium oxide. Star rubies and sapphires can also be produced by surface diffusion technique, with red and blue being the most common.
Synthetic star corundums by the Verneuil (flame fusion) process are made by adding 0.1-0.3% of titanium oxide to the mixture. The stones are known as Linde stars in the trade and are currently manufactured in several colors, with red and blue being the most common. Identification of synthetic star corundum is not difficult because the needles are usually much smaller than those in the natural stone, and they are more evenly distributed.
Star quartz is sometimes used to imitate star sapphire. The silk usually consists of rutile intersecting in three directions or sillimanite (fibrolite). This may result in a four-rayed star or a six depending upon how the stone is oriented.
Star diopside and star entstatite are two inexpensive stones which are confused with one another. Both display 4-ray stars which meet at almost 90° and one ray is slightly more diffused than the other.
Star beryl is an unusual type. Brown in color and displaying a weak 6-rayed star, it bears a strong resemblance to black star sapphire. The star results from plates of ilmenite and hematite which are oriented in certain positions parallel to the basal plane. These plates also appear to give the stone its dark brown color; if viewed parallel to the plates, clear transparent areas are seen.
The color of star spinel varies from reddish purple to black, with most being quite dark in tone. If the stone is cut so that base is parallel to an octahedron face, a 6-rayed star will be seen; if the stone is cut so that the base is parallel to a cube face, a 4-rayed will be seen. In either case, additional stars will be seen around the girdle. Asterism may also be seen in almandine garnet and moonstone.
In a star ruby or sapphire, titanium oxide is exsolved as fine needles of rutile. They orient themselves in three directions, intersecting at 60° and 120° within the same plane producing beautiful stars. The most desirable black star sapphires are those which exhibit the golden star and can be many times more valuable than the more common white-rayed black star sapphires. The asterism of black star sapphire is due to perfectly oriented intergrowth of elongated hematite lamellae. Asterism can be produced in certain types of non-asteriated corundum by moderate heating, if a piece of natural corundum contains enough titanium oxide. Star rubies and sapphires can also be produced by surface diffusion technique, with red and blue being the most common.
Synthetic star corundums by the Verneuil (flame fusion) process are made by adding 0.1-0.3% of titanium oxide to the mixture. The stones are known as Linde stars in the trade and are currently manufactured in several colors, with red and blue being the most common. Identification of synthetic star corundum is not difficult because the needles are usually much smaller than those in the natural stone, and they are more evenly distributed.
Star quartz is sometimes used to imitate star sapphire. The silk usually consists of rutile intersecting in three directions or sillimanite (fibrolite). This may result in a four-rayed star or a six depending upon how the stone is oriented.
Star diopside and star entstatite are two inexpensive stones which are confused with one another. Both display 4-ray stars which meet at almost 90° and one ray is slightly more diffused than the other.
Star beryl is an unusual type. Brown in color and displaying a weak 6-rayed star, it bears a strong resemblance to black star sapphire. The star results from plates of ilmenite and hematite which are oriented in certain positions parallel to the basal plane. These plates also appear to give the stone its dark brown color; if viewed parallel to the plates, clear transparent areas are seen.
The color of star spinel varies from reddish purple to black, with most being quite dark in tone. If the stone is cut so that base is parallel to an octahedron face, a 6-rayed star will be seen; if the stone is cut so that the base is parallel to a cube face, a 4-rayed will be seen. In either case, additional stars will be seen around the girdle. Asterism may also be seen in almandine garnet and moonstone.
Helvetica
(via The Guardian) Andrew Dickson writes about (Helvetica) typeface and its creators + the movie @ http://arts.guardian.co.uk/art/design/story/0,,2127233,00.html
In pictures: Around the world with Helvetica
Happy birthday, Helvetica
I liked it.
In pictures: Around the world with Helvetica
Happy birthday, Helvetica
I liked it.
How To Buy Gold
Moneyweek explains in detail how to buy gold + the do's and dont's @ http://www.moneyweek.com/file/11428/how-to-buy-gold.html
Useful links:
Goldmoney.com
Kitco.com
Bigcharts.com
Stockcharts.com
Useful links:
Goldmoney.com
Kitco.com
Bigcharts.com
Stockcharts.com
How To Profit From Scarcity
Harvard Business School professor John Quelch writes about the concept of creating the illusion of scarcity + other viewpoints @ http://hbswk.hbs.edu/item/5776.html
Blog: Marketing Know: How
Blog: Marketing Know: How
Odd Man In
Paul Gardner writes about the world and work of Richard Tuttle + other viewpoints @ http://artnews.com/issues/article.asp?art_id=1508
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