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Post by radio on Dec 18, 2013 18:50:14 GMT -5
I bought a couple of old stock Linde Boules and cut a couple of pieces about 6mm thick and like slicing a hot dog into small circles. I was disappointed with the results, so wondering what I might have done wrong? I domed it almost down to the bottom edges like I have seen pictures of sapphires. I also bought some Cornflower Blue already cut into rounds and they have an incredible star! I have enough left on the one piece of gorgeous Raspberry material for a couple more rounds but am waiting for advice
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Deleted
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Post by Deleted on Dec 19, 2013 14:25:59 GMT -5
are the boules czolchralski or flame fusion??
If flame fusion, then I am told they my be split in half longwise to relieve internal stresses. Perhaps the raspberry material is more sensitive to this?
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Post by orrum on Dec 19, 2013 17:42:54 GMT -5
Linde stars were made by two outfits. The inventors and then Union Carbide. Some of the older Linde stars only appear on the surface and can be ground off. Does your boule have a L on it somewhere? You might have to use a magnifying loupe to see it.
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Post by radio on Dec 19, 2013 20:15:21 GMT -5
are the boules czolchralski or flame fusion?? If flame fusion, then I am told they my be split in half longwise to relieve internal stresses. Perhaps the raspberry material is more sensitive to this? I'm not 100% sure. They have a glass rod sticking out one end.
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Post by radio on Dec 19, 2013 20:23:16 GMT -5
Linde stars were made by two outfits. The inventors and then Union Carbide. Some of the older Linde stars only appear on the surface and can be ground off. Does your boule have a L on it somewhere? You might have to use a magnifying loupe to see it. I did not examine it for an "L" before I cut it, but don't see one on the remainder of the Boule. I bought them as old stock Linde though. The one I cabbed so far has a gorgeous cat's eye effect, but no star. Perhaps I cut the slice too thin? Maybe a dud Boule? The smaller slices of Blue that I bought have an outstanding star. I have been told that a star in synthetic doesn't move, but a natural sapphire the start moves as the light shifts. The star on the Blue will travel from edge to edge in all directions under strong light and makes even unimpressionable me say "WOW"!
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Post by orrum on Dec 19, 2013 20:30:08 GMT -5
Maybe you have to orient the star b4 cabbing or even sawing. You do with star rose quartz.
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Post by Deleted on Dec 19, 2013 22:35:07 GMT -5
are the boules czolchralski or flame fusion?? If flame fusion, then I am told they my be split in half longwise to relieve internal stresses. Perhaps the raspberry material is more sensitive to this? I'm not 100% sure. They have a glass rod sticking out one end. I did some googling. They are flame fusion. Glass rod sticking out MAY be pure clear corundum.
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Post by radio on Dec 20, 2013 19:56:49 GMT -5
I'm not 100% sure. They have a glass rod sticking out one end. I did some googling. They are flame fusion. Glass rod sticking out MAY be pure clear corundum. Thanks for the info. I knew synthetic Ruby was made with flame fusion, but didn't know Star Sapphire was. I had always heard of "lab grown" sapphires, so never equated flame with that for some reason.
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Deleted
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Post by Deleted on Dec 20, 2013 20:19:30 GMT -5
Sapphires of all colors, including the special ones we call ruby, are made by two methods.
Flame fusion is an additive method were they sprinkle powder thru an intense hydrogen flame and it melts onto the surface of that before it cooling rather quickly and building a cylinder. This rapid cooling leaves internal stresses. Today these stresses are released by slicing the cylinder lengthwise. In the old days some were annealed. That is it was heated hot enough to relieve stresses and then cooled slowly so as to not induce more.
The other method is the czolchralski method. This is a "pulling method" in which a seed crystal is heated to just below melting and is dipped into a molten pool of corundum. The surface of the pool solidifies onto the seed crystal which is then slowly 'pulled' upward while rotating. The seed crystal slowly grows longer and wider up to the maximum width of the crucible. The finished product is called a 'boule'. Czolchralski crystals can be quite HUGE in that it is possible to pull a 25kg single crystal sapphire that is 200mm (8") in diameter. This method is very common and is how computer chips are made as well as solar cells for producing electricity from sunlight.
I once saw a silicon "boule" that was easily 5ft long and the full 200mm in diameter. It was huge and heavy. The original seed crystal was still at one end. It was 5mm in diameter. That entire, nearly molten, boule hung from a single little 5mm cylinder. Silicon is amazing stuff!
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Post by Rockoonz on Dec 22, 2013 1:49:10 GMT -5
I did not examine it for an "L" before I cut it, but don't see one on the remainder of the Boule. I bought them as old stock Linde though. The one I cabbed so far has a gorgeous cat's eye effect, but no star. Perhaps I cut the slice too thin? Maybe a dud Boule? The smaller slices of Blue that I bought have an outstanding star. I have been told that a star in synthetic doesn't move, but a natural sapphire the start moves as the light shifts. The star on the Blue will travel from edge to edge in all directions under strong light and makes even unimpressionable me say "WOW"! All the star garnets and star sapphires I have seen are high domed, almost hemispherical. I think you may need the high dome to get the star effect. Lee #2
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Post by orrum on Dec 22, 2013 9:26:50 GMT -5
With star rose quartz you make a rough sphere and then find the star, there will be one on each side, make a dot with a sharpie at the star center and saw it in half. Thay way you get two preforms.
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Post by Starguy on Jan 14, 2014 20:45:32 GMT -5
New here, but this post got me to sign up. I have 7 Linde boules, one cornflower blue about 5" long and 6 Bahama blue about 1.25" long. All show extremely bright stars whether polished flat or domed. I haven't sawn them, only polished the end of the boule. I have been able to tell that the boules had stars even before they were cut because the legs of the stars were visible along the sides of the boule. I wonder if you got some more recent foreign boules or possibly a cats eye boule. I'll try to post some pictures if I can figure out how.
Linde (Union Carbide) quit making them in 1974.
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gemfeller
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Post by gemfeller on Jan 15, 2014 0:03:20 GMT -5
Welcome to the Forum. I was going to post to this thread when it started but didn't because I wasn't sure how the optical axis of Linde star corundum boules was oriented. If your boules are truly Linde material my question is answered. The top of the stone should be perpendicular to the long direction (C-axis) of the boule to show a star. If the top of the stone is perpendicular to the A-B axis you'll probably get a cat's-eye effect, not a star.
That's the way it works in natural corundum crystals. I've cut quite a few natural star rubies and sapphires and the important clue is finding the C-axis. Or you can hunt-and-orient on the fly (usually my method once you find the growth lines, LOL.)
I'm surprised Union Carbide boules are still around. I remember back in the 1970s when most of their stock apparently was acquired by a New Jersey company called Elvin (I think.) My recollection is that Linde star cabs had an incised "L" on the back but I'm not sure about the boules. Since the Union Carbide patent expired numerous other types of syn. star corundum have been marketed from Israel, Japan, Russia, Switzerland and I'm sure other sources. Rick
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Post by Starguy on Jan 15, 2014 0:15:08 GMT -5
That's the way it works in natural corundum crystals. I've cut quite a few natural star rubies and sapphires and the important clue is finding the C-axis. Or you can hunt-and-orient on the fly (usually my method once you find the growth lines, LOL.) :You are exactly correct. Linde boules orient on the c axis just like natural star sapphires. I never thought that one could be polished on another axis, but that would probably yield a cats eye.
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gemfeller
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Post by gemfeller on Jan 15, 2014 12:11:00 GMT -5
Starguy, I looked up some of the patent info and learned they were able to create some boules that yielded stars in different orientations. There were many experiments by several people and I ended up not being sure what Linde finally settled on.
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Post by Starguy on Jan 15, 2014 20:10:38 GMT -5
Starguy, I looked up some of the patent info and learned they were able to create some boules that yielded stars in different orientations. There were many experiments by several people and I ended up not being sure what Linde finally settled on. That's really interesting. I never thought about that because every boule I've seen was oriented on the C-axis. I can imagine that they experimented with different methods though. I have a cornflower blue boule that is 185 carats. It's enormous at 5" and 14 mm at the business end. The ones I've found recently on ebay are short, less than 1.5". A lot of them are oval too, with the rays poorly oriented for an oval cab. That Linde material is fun to cut because it's close to perfect. Hard to put a cursive L on the back though . You would need a laser to do that properly. I realize they aren't worth much due to the number produced, but I can't resist anything w/ a star. I cut my teeth on high quality Idaho garnet. They're a pain in the @$$ to orient. linde makes it easy.
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gemfeller
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Post by gemfeller on Jan 15, 2014 21:44:57 GMT -5
I wish I could remember my search criteria but can't. I found a couple of patent histories that discussed methods for annealing the boules to orient the rutile crystals. If I didn't misinterpret the text, a couple of them resulted in a star orientation different than the c-axis.
I don't know how they put the "L" in the backs. My best guess is with an ultrasonic die.
I'm also a "phenomenal" gem fan and star garnet "veteran." Star corundums seem simple to orient after chasing the wiggly legs of star garnets to get the apex dead center. Worse, most of them yielded such faint stars that a rock shop owner I knew said "A friend is someone who can see the star in your garnet." There are really strong stars, of course, but they were few and far between in the rough I cut.
I recently was given some extremely fine Hogg Mine rose quartz I'm sure will produce stars. But it seems I always have so many projects underway something is always overlooked. Thanks for the reminder. Now if I can just figure out an easy way to make some small rose quartz beads...
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Post by radio on Jan 15, 2014 22:02:26 GMT -5
That's the way it works in natural corundum crystals. I've cut quite a few natural star rubies and sapphires and the important clue is finding the C-axis. Or you can hunt-and-orient on the fly (usually my method once you find the growth lines, LOL.) :You are exactly correct. Linde boules orient on the c axis just like natural star sapphires. I never thought that one could be polished on another axis, but that would probably yield a cats eye. Thanks for the info. I will hit the sides of the boule on the wheels tomorrow and see if I can find the star. The two cabs I cut from it already have a very nice cats eye, but that's a long ways from a star
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