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 Post subject: how much accurate is the presidium gemtester?
PostPosted: Fri May 25, 2007 4:04 pm 
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Hi ,
I had purchased a presidium gem tester last month. the shopowner where i purchased the gadget said that the presidium gem tester is a helpful tool in identifying most of the gemstones.It is based on the principle that different gemstone have different thermal & electrical conductivity and this gadgets differentiates them on the basis of their thermal and electrical properties.
But I am not satisfied with the accuracy of this gadget since the built in analog meter sometime detect emerald as quartz while some time as iolite.,there is no consistency in the analog meter display.
I want to know the valuable opinion of the members of this great mailing list,whether one should rely on such instruments? :?:

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PostPosted: Fri May 25, 2007 6:23 pm 
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This tester is a thermal conductivity tester and is a further development
(I hope ) of the thermal conductivity tester designed to differentiate diamonds from everyting else (except they dont work to distinguish moissanite , a relatively recent development) When I saw a picture of this instrument with labels for various types of stones I thought it might be a good idea and hope to play with one of these before too long.

That said using such an instrument can/should only provide an indication of what a stone might be. Other than the above,, thermal conductivity measurements have been qualitative rather than quantitative. Also such measurements are likely to be very dependent on the temperature of the specimen , the ambient temperature, the state of the units batteries, possibly the recent measurement history of the probe or the stone or both , and how hard and consistently you press the probe onto the stone,, to name a few that I can think of.

If I had one of these instruments I would develop a set of check stones or pieces. Different types of glass, different faceted stones perhaps a ball bearing or two. Put them in a medicine vial in the fridge and test them starting at a constant temperature and see if the instrument doesnt behave a bit more consistently. I hope it does because I think it is a good idea.

But it is not a first line ID instrument and at this time you couldnt mention results from it in a courtroom for example. Just something to help confirm a trend or suspicion in other data.


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PostPosted: Fri May 25, 2007 11:06 pm 
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Gene is correct, rishi. Once you test a stone with the pen the stone's temperature is elevated, and reading again will not give the same result. Let the stone return to its original state, and then retesting should give the same result as when originally tested.

When you're getting an obviously incorrect reading, try cleaning the stone, and testing on other facets to see if that helps. Otherwise, possibly an inclusion is interfering, or maybe it could even be filled, who knows. Either way, the machine is just an indicator, IMHO, that must be used in conjunction with your other gemological equipment because there are too many variables such as if the gem is dirty or if it's temperature fluctuates, along with the other things Gene brought up like the battery's power level if you're not plugged in, the temperature the machine reaches while working, etc, so it is hardly a reliable tool for definitive gem identification on its own. Hope this helps. :wink:

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PostPosted: Sat May 26, 2007 1:43 am 
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Thankyou Crystal,
I am quite satisfied with you.As you told the main reason for variations in the result of the same stone tested twice or thrice is the increasing rate of temperature within the stone.i used to touch the pen's probe on to the surface of the stone very frequently without letting the stone return back to its constant temperature and that was why the result shown on the analog meter of the instrument varied every time i tested the stone.
You are right that one should not completely rely on such type of instrument rather we can use it as a supplement with the other traditional but effective gemological instruments in identification of a gemstone.
Thanks,
Rishi. :D

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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Wed Nov 07, 2012 5:08 am 
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I have bought a black checker board spinel.

Description Genuine natural unheated/treated item.

I have the presidium dual gemtester it has proved brilliant. It only gives indication of coloured stones as to being glass or not

But having trouble with the spinel I have tested on the flat in between facets and is coming up no gemstone total zilch.

I do realise that heavily included/enhanced stones even diamonds can give a negative reading

Any ideas on black checker board cant really test visually too dense

Thank you

Wildwood


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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Wed Nov 07, 2012 10:59 am 
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We do not support gem testers of this sort on GemologyOnline because they generally unreliable.
Learn to use reliable instruments and you won't have issues.


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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Wed Nov 07, 2012 4:25 pm 
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Hi

I realise what your saying. I use mostly my lense but the stone is very dense


The tester is only part of what I use as one of a few tests.

I have found it very good

Thank you so much for your reply it is appreciated


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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Fri Nov 09, 2012 3:03 am 
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Would you recommend the duo tester instead, which measures both thermal and reflectivity? Or would you recommend the electronic refractive index meter, which is also manufactured by Presidium?


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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Fri Nov 09, 2012 8:02 am 
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Beryllagem wrote:
Would you recommend the duo tester instead, which measures both thermal and reflectivity? Or would you recommend the electronic refractive index meter, which is also manufactured by Presidium?


Hi

I do not know if your question was meant for me, but will answer anyway

I do not have the meter

Will be my next instrument but expensive if you want a good one.

I do have the Presidium duo tester I just bought the newest one (not from Ebay)

I find it invaluable. But you do need to use other tests too because some gemstones conductivity is not much more than glass so you should have some understanding of stones.
Hope this helps a little

Wildwood

I use my lenses more than anything and use my duo as a back up you really need it if buying from Ebay.


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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Fri Nov 09, 2012 10:42 am 
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wildwood5012 wrote:
The tester is only part of what I use as one of a few tests.


And that is exactly how it´s supposed to be used.

I use the Duo-tester and find it very reliable but NOT as a stand alone tester to identify a gem, only as one of "many" tests...

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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Sat Nov 10, 2012 1:00 am 
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Thanks for your replies.


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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Mon Oct 14, 2013 9:09 am 
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Barbra Voltaire wrote:
We do not support gem testers......
Learn to use reliable instruments and you won't have issues.


Please tell me what my first line of trying should be on a gemstone. As an interested amateur what should I get in the way of equipment to test colored stones.

I bought a Gemtrue tester after reading about man made glass being passed off as gems. Gemtrue gives a strong positive response to identifying my diamond ring. On coloured gemstones the colour changes from green to red but only shows one or two of the five or six indicator lights. On one particular "Topaz" it shows no change at all.


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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Mon Oct 14, 2013 1:57 pm 
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A refractometer is a pretty good place to start. I got a used one for 80~ bucks (I think it was originally a JTV-sold one), and they're not hard to use at all. It will at least separate glass with its distincitly low RI from most gems, and combined with other data it's a good general tool for identification. Lots of gems have overlapping RIs so it alone won't tell you what it is but it narrows the field quite a bit.

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 Post subject: Re: how much accurate is the presidium gemtester?
PostPosted: Mon Oct 14, 2013 2:28 pm 
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Scarodactyl wrote:
A refractometer is a pretty good place to start. Lots of gems have overlapping RIs so it alone won't tell you what it is but it narrows the field quite a bit.


Thank for your suggestion. I 'll see if I can find one.

My most pressing problem is sorting the gemstones from the glass. I have a microscope so perhaps it's time to check my troublesome Topaz under its lens.


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