testing of rough - mystic?

[edward]

Hello to this terrific side,

I understand: roughs don''t give RI, VG is tough, color is hard to be sure off and so on, plus they are very much subject to the lapiadry''s later craft and judgement.

I saw this very old Sri Lankan selecter going through 5 kilo freshly digged up stones in about 1 minutes, choosing 20 carat out of it. UH!

The workers, the mine owner and so on, totally trust his descision. No second thought!

My Q: What test instruments could a greenhorn use in oder to catch up with his experience?
Hardness test works, right?
Can gravity be measured in rough or does the uneven surface change the result?
Ultra violet works.
Dichroism?

Thanks for some hints or experience on te

sting rough.

Ed

 

[yowahking]

Not sure what your level of interest is. If you are new to this, catching up with his expert level takes either time, or having someone teach you. Short cuts rarely work with evaluating rough. I have been doing it for 18 years and still do not feel good at it. Mostly because I am not a cutter. If I actually cut the stones, I would learn faster. Tried it, no good at it. If you are already in the business, you are in the right country for learning about rough. There is no shortage of it. You may try visiting with a cutter, and asking for tips. Sapphire rough is much different from Topaz rough. If you give me more specific info, I may direct you to some of my friends there. Mogok on this sight probably has some insight as well.

 

[strmrdr]

The fast road to learning it is take the classes that Mogok talks about.
Look around you will find the info about them.

link:
http://www.aigsthailand.com/

 

[edward]

Hi Scott,

yes, I am seriously about getting into gem trade. I came to Sri Lanka on other purpose, but that has vanished. I would like to search for rough Taaffeite, if that is somehow possible.

I would certainly be willing to invest time and money in instruments to do so. I might buy mauve spinel, cut them and test them for DR, but may be there is a smarter way.

Yes, I would surely appreciate some local contacts. And I would also try my luck in a cutting course. So far I only found one guy who does trainings for cash in Colombo and he was no good at all.

Ed

 

[yowahking]

Most rough Taaffeite is not going to be available to you. Collectors usually have long years of contacts for those type stones. Try Supershine for your spinel as they cut it, you are welcome to tell them my name. I see them a couple times year in the states. Why Mauve spinel? I love spinel just curious about color. Purple scapolite is also fun to work with.

 

[edward]

That doesn't sound encouraging for my Taaffeit-quest. I thought most Taaffeite is found from mauve spinel (or light blue).

On Monday I will be shown a newly found 112 carat blue sapphire rough. How could I, beside lense and lamp, check such a stone? It will not be fake and is certified, but I still dont know which instruments are usefull to test rough (beside color and later cut)?

Anybody some advice?

 

[Michael_E]

Ed,
If you know that the sapphire is natural, what are trying to test for ? Any test that you might do will only answer some question that you might have. Some questions have no tests to answer them, other than experience. Questions such as:
What color and saturation can I expect after cutting ?
How large and what quality of finished stone can I expect ?
What shape should this stone be cut into and How many pieces ?

To answer these questions you would have to be a cutter with some years of experience. If you don't have the experience someone who does can give you some guidelines, but they are very general and may not apply to the rough that you are looking at. Sapphire and many other stones are pleochroic and have to be oriented not only for best weight retention, but also best color. Often these two things are at odds and a decision needs to be made as to whether best color or best size will win out. Here are some guidelines that are very general and they assume that you KNOW that the rough is natural.
1. Use a strong penlight to shine into the rough from all directions in an attempt to see the flashes from cracks or other inclusions. If you need to you can coat the rough with mineral oil or some other liquid so that a rough skin is less visible. If you don't have anything else water will do. PLease don't lick the stone...that's gross !

This penlight examination DOES NOT tell you anything about color except the direction of orientation for the best color, (maybe, since colors "mix" in stones with many axes of symmetry, like rounds).
2. Place the stone on a sheet of white paper. If it looks really dark or black, then it will need to be cut into multiple pieces to get the thickness down to where you can see the color saturation that you want. Any stone that looks dark on a sheet of white paper in fairly bright light will be just as dark when it's cut.
3. LOOK at the rough. Measure it and see what you think you can get out of it. If the color's dark, then this step is less important since it will have to be cut anyway. If the color is good, then the depth of the stone, in the direction that you want to cut it, looking at the proposed table, will need to be at least 60% of the proposed width. If there are any pits or other inclusions that need to be cut out, you will need take that into account as far as the potential shape or size that can be had.
I hope that this helps, but you really would be better off if you could take an experienced cutter with you.

 

[edward]

Michael,thanks.
In case of this 112 carat I know it is no fake because it has been seen by a few people I trust. Judging its quality after cutting is one step after.

BUT: if someone offers me 5 yellow rough midsize sapphire at the mine, can I quickly check whether they really are sapphires? Is that a stupid question?

 

[Michael_E]

Ed,
That depends on what gems that mine can produce and you are confident that the stones you are looking at came out of that mine. Specific gravity is a good separator of spinel and corundum, as long as they are clean and there are no trapped bubbles. This won't work if you are trying to separate garnet and corumdum though.
To tell you the truth, I think that if you are going to do this you'd be better off with a lot of education and a good small portable gem lab or you need to live at the mine and make sure that nothing is getting "salted" into the goods that you are looking at buying and separate them later. Regardless, you absolutely need education, experience and the tools that go with this or you will eventually lose your money to someone unscrupulous.

 

[spinel]

Hello Edward, if I was you I would bring the roughs to Bangkok and have them identified by AIGS lab. The lab is just 2-hours flight from Ceylon. Always be able to have the money back even you have very trustfull contacts (he or she could make error too). Before all it is your money and more than that, your reputation - which is the most valuable thing for a gem trader - is at stake.

I pay (very) high respect to fakers who nowadays succeed to achieve very great level of marvellous things! You will not believe it until you live it.

Hopefully it will not happen to you. Best wishes. Spinel

 

[yowahking]

Ed, you need to find a couple of people who are willing to show you the ropes a bit. Look up Ellawala and ask them to refer you to someone who may have the patience for a new person who is interested in learning. Very highly respected gem family in Sri Lanka. Suresh is the son and my friend, the father I do not know but a real gem God over there.

 

[edward]

Thanks everyone for the advice. I'll follow them.