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 Post subject: Ruby cutting and Polishing
PostPosted: Fri Aug 08, 2014 9:16 am 
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We have Australias only commercial deposit of Ruby, mainly in Hard Rock.
I am interested in receiving advice for cutting Cabochon Ruby at this stage, and Ruby in the
mother Rock, slight doming and various shapes, we are having problems in polishing the Ruby, due mainly to pitting, it just takes forever.
We have been cutting and polishing Yowah Opal since 1972, but the Ruby is getting us
very frustrated to say the least.
What are we doing wrong ??


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Fri Aug 08, 2014 10:30 am 
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Depends on what you are doing.

Best detail your current procedure and I'm sure the diagnosis will follow.


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Fri Aug 08, 2014 1:02 pm 
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Assuming you are using diamond for cutting and polishing, then try skipping from 600 mesh directly to 3k or 8k for pre-polish. For some reason, I have found, that ruby and sapphire both do not like 1200 mesh diamond. I had the same problem cabbing some Afghani ruby years ago and read about 1200 mesh causing pitting in carving synthetic ruby in book on gem carving (maybe Hunt's book). Once I skipped 1200 then the pitting stopped.

For polish you need 60K diamond. Ruby should polish very fast if you have done your work in the pre-polish stage.


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Sat Aug 09, 2014 9:06 am 
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Sean Lines wrote:
Depends on what you are doing.

Best detail your current procedure and I'm sure the diagnosis will follow.

Hi thanks for your interest.
we are using Diamond Pacific Machines, with Galaxi and Nova wheels, this works well with
Yowah Opal.
Galaxi 100 then 220 then 220 Nova , 600 Nova, 1200 , 3000
tried following with 14000 Nova and 50,000
most roughing is done with the 220 Galaxi plated wheel then Nova 220 etc
all those wheels are run with water only, reducing the amount of water as the wheels get finer
Am I using the right machines or wheels ?


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Sat Aug 09, 2014 7:55 pm 
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Hi, Uwe, cutting/polishing Ruby is so far removed from opal, even opal in ironstone, that you must set up a dedicated plant to cut it.
You must remember that corundum is hardness 9, and opal, way down the scale.
It will take much more time to shape, and polish.
Specialised laps are available to shape, one example is the "crystalite Star-lap", I'm sure there are many new ones available, as mine is 20, or more, years old.
Andrew, at "Aussi Sapphire" will be a big help to you, if you contact him.
You may also be dealing with material that is so included/fractured, that you will never be able to get a good polish, and the pitting you are seeing is a product of the included materials saturating the stone.
Please post some shots, I'd love to see what you are finding!
Good luck, Barry.


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Sun Aug 10, 2014 6:38 am 
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Hi Barry,
Thanks for your comments, I have started to come to that conclusion also, but was hoping
that it is not necessary. As I have plenty of good Opal cutting gear, as I also import much
of the Diamond Pacific Machines and wheels.

I would like some feedback , what type of Machines would be good, we have one Faceting Machine but never used. There seems to be various opinions on type cutting and polishing
wheels good for Ruby, but our initial interest is in Cabochons and slight
doming of Ruby in white Anorthotite Rock and Black Hornblende.
Regards Uwe


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Mon Aug 11, 2014 8:25 pm 
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I have not been successful at polishing ruby with nova wheels (600 and coarser is probably ok) . The diamond pacific machine is fine, but you may want to make some hardwood wheels and charge with diamond paste for prepolish and polish. That worked for me. The nova wheels seem to give too much to polish ruby.

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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Tue Aug 12, 2014 7:04 am 
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Hi Uwe, I agree with Nathan on the polish problem.
My grooved star-lap is a hard plastic, runs flat on a Facetron , and is charged with diamond compounds.
As Nathan says, hardwood will work, and if you find some-one with a lathe, they can turn one for you.
The size of the groove can be your choice, and is dependant on the size cabs you want to make.
Considering how likely the rough is to fracture, and shed pieces, some hardwood is probably the safest, cheapest way to go.
Barry.


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Tue Aug 12, 2014 10:05 pm 
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As Tom Kidwell said you should try different series of grits. This old faceting article clearly shows the pitting issue that pops up at the pre-polish stage on ruby and sapphire. http://www.gemsociety.org/article/just- ... ple-heart/

I personally never had any luck with the 14k or 50K Nova's so you might try skipping those and going to a spin disk polishing pad with either 50K diamond or Alumina Oxide.

When I have the chance I'll try and polish a piece of montana sapphire and see how it goes. I have 220 plated, and then 220, 600, 1200, 3000, 8000 Nova's on my setup with a leather polish pad for Alumina on the end.

Steve

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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Mon Aug 25, 2014 6:00 pm 
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Found a few pieces of tunduru rough. Polished a window in one and tried a few different sequences. Best was 220 hard, to 280 Nova, to 600 Nova to 8000 Nova.

But the experiment wasn't entirely successful. Started to pick up a polish on the 600 which was not ideal. Plus the stone had small crystal inclusions that wan't to pull out.

Seems like a harder wheel might be better.

One option might be the Hitech diamond discs and backing plates without the sponge pad. You can run these on your faceting machine. Although a wood wheel might be safer as has been mentioned.

Steve

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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Fri Aug 29, 2014 4:01 pm 
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Your issue is with the 1200 wheel. For some reason, corundum lattice structure in the crystal at certain orientations, hits the spot where the 1200 pulls chunks of material out of the stone instead of cutting it. This causes subsurface damage as well, which only shows up in the final polish causing inventive cursing and gnashing of teeth. Skip the 1200 wheel and finish with 50k on a felt buffer (be careful of heat build up). That should work fine.

Ruby has been one of the hardest corundums i've cut, so it may go a bit slow.. you'll have to see how your deposit works out.

good luck!

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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Fri Aug 29, 2014 8:46 pm 
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FWIW, I have had surprisingly fast, excellent polishes on star ruby and Linde` star sapphires using hard felt and Alumina A (0.3µ). Usually, I am a Diamond Fan, but in this case I feel the results are undeniable.
My hard felt has worn grooves which serve very well at correcting tiny flats and dishes, and assuring a curve remains a curve. And the water medium resolves any heat issues.
Only drawback is that, being felt, it does smell like a wet sheep, if heat is generated.

I realize that in some places, for some people, that could be erotic, and perhaps make the gemcutting more pleasant for some.
I don't care for it, but Suffer For Art.

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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Fri Aug 29, 2014 10:25 pm 
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:smt001


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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Sat Aug 30, 2014 6:01 am 
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Relax, Barry. That wasn't regional. Matter of fact, the first person executed here in the Plimouth Colony was a young gentleman caught "helping a sheep over a fence". (They killed the sheep, too. History does not record if it ever made it to the table.)
We are presently testing a non-sheep-origin copolymer composite for just this purpose, on a faceting lap baseplate. Looking good.

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 Post subject: Re: Ruby cutting and Polishing
PostPosted: Sat Aug 30, 2014 1:50 pm 
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Gearloose wrote:
Relax, Barry. That wasn't regional. Matter of fact, the first person executed here in the Plimouth Colony was a young gentleman caught "helping a sheep over a fence". (They killed the sheep, too. History does not record if it ever made it to the table.)
We are presently testing a non-sheep-origin copolymer composite for just this purpose, on a faceting lap baseplate. Looking good.


no good deed goes unpunished!


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