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 Post subject: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 12:24 am 
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Hi all, new to the forum and just posted my newbie introduction in the thread.

I am looking for people who have used Presidium (or similar) instruments for testing a) coloured stones and b) diamonds for ROUGH stones.

I understand all the synthetic and Moissanite cut stones on the market (actually have quite a lot of them) but quite keen to purchase test equipment that can also test rough stones so trying to look for reviews from experienced people who have used them.


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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 2:11 pm 
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Some previous posts on Presidium products. There are several if you do a search on the left.
viewtopic.php?f=11&t=23262
viewtopic.php?f=34&t=20458


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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 2:44 pm 
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You should post the specific product models your looking to get an opinion on. Or is it just the brand in general?

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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 2:50 pm 
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Yes. With the exception of the Presidium thermal diamond tester, not the Presidium diamond/moissanite tester, I have found the instruments unreliable.

In our business, selling something with a wrong ID (even when arrived at innocently) can destroy one's reputation very quickly....especially with internet reviews.


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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 4:18 pm 
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We have found the same in both Presidium and Gem Oro brands, unreliable and inconsistent. Where it is just a means to an end result, where a more gemological test needs to be done to be definitive.

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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 4:24 pm 
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There is only one device for getting consistent accurate results on rough stones. It is called a Raman Shift Spectrometer.

The Presidium and all the "magic" testers are junk and will give you unreliable results. Forget about them.


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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 9:03 pm 
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Every word of 1bwana1's post is absolutely correct.
Listen, grasshoppers.


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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 9:33 pm 
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Thank you everyone. Yes, I was specifically looking into this brand and I am glad to have joined this forum as this is the feedback I wanted to receive.

I normally fossick & mine for sapphire in Central Queensland, Australia so very easy to identify the materials found (Sapphires, Zircons, Spinel).

About 25 years ago I inherited a very large Collection of rough stones with test equipment (refractometer, polariscope, dichroscope etc) found in the 1970-80’s.

I remember stories about these when I was young but just kept in my collection because have enough rough sapphire of my own and rough opal (from friends mines) that I will never get to it in my lifetime.

Recently my wife and I have both started to cut our own stones again because our cutters are too busy (the good ones here have over a year lead time).

It has made me think more about learning to expand my skills a bit. Here is a picture of some rough stones that we were playing with this weekend.


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 Post subject: Re: Presidium instruments experience
PostPosted: Sun Apr 25, 2021 11:30 pm 
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Do you still have those instruments, Pythonrob?


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 Post subject: Re: Presidium instruments experience
PostPosted: Mon Apr 26, 2021 2:14 am 
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Nice collection of rough.


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 Post subject: Re: Presidium instruments experience
PostPosted: Mon Apr 26, 2021 2:36 am 
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Yes, used the refractometer on cut stones but was a bit concerned as the oil is quite old and found out it was very toxic smells bad and stained my fingers. I tested the RI on my purchased certified cut stones (sapphire, amethyst, citerine, tanzanite, aquamarine) and they all were spot on.

Some of my rough stones have of small faces grinded/polished onto them so appears they have undergone some testing in the 1980’s. I did not know how to test them as the RI only goes to 1.9? On the refractometer and they don’t have a table.

I then used UV blue light, cheap diamond tester, polariscope and home made a SG tester from a wire frame, jewellery scales, distilled water and checked using both cut and rough stones. The diamonds for both rough and cut showed 3.5-3.52 and the zircons 3.93-4.7? ish.

This is what prompted me to look for other equipment.........

I do appreciate your response(s). Back in the 1970’s here coloured diamonds were often scrapped or crushed into industrial tooling. I was then told Tiffany’s started buying yellows then much later names appeared such as champagne, cognac, brown, blue, pink, red etc. Some of the odd shapes, off-cuts were also sold off so still in collections today.

Everyone may have heard of “Argyle / Kimberley” diamond mine but there was also Bow River, Gibb River and Ellendale. They are now going back over these old sites again now and starting to get a lot of success but they are so remote it is hard to get people who will work there.

Sorry if my response was a bit long but I heard sometimes it helps to give some background to where items were discovered.


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 Post subject: Re: Presidium instruments experience
PostPosted: Mon Apr 26, 2021 12:35 pm 
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Great news!
Clearly the instruments you already own are reliable and useful.
Identification is essentially the process of elimination when using standard gemological instruments. Your brain is the dedicated software which will disqualify possibilities.

Have a routine you follow for ID.
1. Start with the polariscope. Singly or doubly refractive? Eventually,learn to use a coniscope for further elimination.
2. Refractometer with polarizing plate for birefingence (Birefringence can be as important as the actual refractive index, take copious notes) Not that many gems are OTL on the refractometer. Once you seperate the singly refractive from the doubly refractive, you've narrowed down your choices significantly.
3. Specific Gravity By this point, your possibilities will be quite limited.

Notice that I have not suggested a look at the unknown with magnification....yet.
Why, #-o that's the first thing people usually do!
Because, as soon as you look at the unknown, your brain starts to automatically identify it. It is human nature to make the test results confirm your first impressions. Bad, not a reliable scientific approach.
Let the instruments identify the stone without bias from first impressions.
Now, look at the stone with the scope.

Hope this helps.

Also, I highly recommend the downloadable software: Gemology Tools Professional

You would have wasted hundreds of dollars on an unreliable gizmo, just buy GTP, you will never regret it. Go with the magnet add-on.


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