Find your diamond
Find your jewelry
shape
carat
color
clarity

I bought a presidium gem tester... and you should too

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
I have enough jewelry to warrant me buying a presidium gem tester. I also wanted to test a rock quartz antique locket I bought.

It arrived and I just tested all my jewelry:
Fun experience...
2 lockets with stones
1 rock quartz locket
11 rings
6 gemstone pendants

The results... all passed... except 1 ring and 1 pendant by a well known jeweler many use here.
The pendant had blue stones sold as tanzanites and purple stones sold as sapphires. The blue stones barely register as glass. The purple register as somewhere around spinel.
The ring I had custom made also had sapphires. the center one tests for sapphire. The smaller stones, again, do not. I've tested all 16 of the outer stones.... not 1 tests as sapphire....Possibly topaz or something even lower around 5 ish....

So I reset the tester... over and over, same results at least 5 times...Only on those stones.
I considered it was due to the size of them (under 3 mm) so I tested all the other stones in my rings under 3 mm. Stones by other sellers passed, (including the spinels from voce that were 3 mm, and a ring I bought off LT with 1 mm reddish spinels on the side).
I tested some quality beads I bought to make bracelets (small). All passed

So this leaves me with the conclusion that this seller is not using the stones they claim, or they are buying stones and are being lied to about what they are buying.
But I'm going to send the pendant and ring out for outside testing now to confirm.... It has me confused and very disheartened if this is true. I am hoping its not.

If you have custom jewelry made... get it tested!
 
Last edited:

OoohShiny

Ideal_Rock
Premium
Joined
Apr 25, 2014
Messages
8,192
Was the jewellery Brand New or a pre-loved item?
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
All brand new one from their shop made to sell another one custom made

prisidium May not be considered accurate but it’s strangely accurate on 100% of my stuff without question so it’s selectively inaccurate on items from the same seller
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
Did some quick search for more reviews of the presidium and I don’t really find anything negative about the accuracy but I’ll keep looking
Seems to have overwhelmingly good reviews of functionality
 

JackTrick

Shiny_Rock
Joined
Jul 23, 2019
Messages
301
From the gemology/gemologist groups I frequent, I have never heard anyone praising the accuracy of presidium gem testers. Moreso that they tend to be unreliable (with both false positives and negatives).

They are certainly appealing to purchasers/mass-market looking for an easy and accurate tests of gemstones, and I think that's why they're often well reviewed by individuals (despite not having any guarantee towards reliability). Colored stones are a wild and wacky world of identification.

I do absolutely encourage you to get your stuff checked out, but I'd recommend a local trained gemologist (if you can find one).

Alternatively, for some of them, we can try to talk through other ways you can test the stones for authenticity. Tanzanite/glass we may be able to narrow in on with the use of some polarized light.
 

LD

Ideal_Rock
Premium
Joined
Jun 29, 2008
Messages
9,876
I have one. I agree with Gene that they're not always reliable and if you're going to use this, perhaps get a few more tools/equipment to back up the readings. It's definitely worth popping along to a jeweller near you to see what readings they get or if they can confirm your thoughts.
 

PrecisionGem

Brilliant_Rock
Trade
Joined
Jul 27, 2004
Messages
1,737
You would do much better with a few simple tools and the book GEM Identification made Easy by Antoinette Matlins.

Or if you want to make your life even easier identifying gemstones buy the software:
Gemology Tools Professional https://www.gemologytools.com/index.html

With this program you enter what you know about the gem such as it's color, transparency, single or double refractive etc. and the program narrows down what the gem could be.

If you have a Dichroscope, Loupe, Chesea filter and add a refractometer, you can pretty much identify almost anything.
 

PrecisionGem

Brilliant_Rock
Trade
Joined
Jul 27, 2004
Messages
1,737
Here is an example.

I have a stone that is blueish purple, and transparent so I enter that information. The program returns 28 possible gems.

GTPRO_1.png

Using a broken pair of cheap Polaroid sunglasses I can see the stones Optical Char is DR or double refractive. So I enter that an the program has reduced the possibilities to 23.

GTPRO_2.png

You may be able to see this with the naked eye, but a cheap Dichroscope for sure shows 3 colors, so the Pleochroism is 3 colors. Enter that and BINGO, the gem selection is reduced to 5 possible stones.

GTPRO_3.png

Now if you had a refractometer you measure your stone around 1.692 and be sure that it's a Tanzanite.

With the refractometer you could also fine tune the Optical Char to know it's B+ (Opticl Char Biaxial, and Optic Sign +) I have a little spread sheet I made where you just enter your readings from the refractometer and the spreadsheet calculates the rest.

Screen Shot 2020-10-21 at 5.09.21 PM.png

With the refractometer it's narrowed down to this:

GTooldFinal.png
 

Bron357

Ideal_Rock
Premium
Joined
Jan 22, 2014
Messages
4,717
I have a Presidum and they are useful But with a BIG caveat.
Yes, it can ID any gems that are glass (CZ) or synthetic Quartz (like CZ). They can ID between amethyst and purple sapphire / spinel, they can ID between garnet and ruby or spinel, ID between citrine and yellow sapphire, ID Jadeite from quartz or glass BUT they can’t ID lab grown corundum or spinel from natural material. They also can’t detect any treatments ie flux filling or BE treatment.
The most common Issue, dare I say deception, is selling lab grown corundum or Spinel as natural and a Presidum can’t distinguish between lab grown and natural ie dug out of the earth. And it matters, a natural sapphire might be $1,000 plus a carat whereas a lab sapphire is worth under $10.
Your best friend when assessing gemstones is a loupe.
Yes, you need to invest some time into understanding and recognising gemstones by colour and what inclusions to expect to find under magnification.
Lab grown material tends to be perfectly even in colour and without any inclusions. Natural material is most often imperfect.
Lab grown material, flame fusion, is grown in a way that creates lines called striae.
There is a range of other pieces of equipment that test other characteristics of gemstones and help determine if treatments have been applied. Highly treated “natural” gemstones aren’t worth much more than synthetic so it is important to know about treatments as well.
 

PrecisionGem

Brilliant_Rock
Trade
Joined
Jul 27, 2004
Messages
1,737
So what kind of stone do you have if the needle goes to the red line?
Could be either Quartz, Emerald, Aquamarine, Tanzanite, Tourmaline, Garnet, Iolite or a host of other gems not shown on the scale.

Screen Shot 2020-10-21 at 5.26.19 PM.png
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
So what kind of stone do you have if the needle goes to the red line?
Could be either Quartz, Emerald, Aquamarine, Tanzanite, Tourmaline, Garnet, Iolite or a host of other gems not shown on the scale.

Screen Shot 2020-10-21 at 5.26.19 PM.png

I dont think people use it for that purpose. it definitely isn't applicable to the thread b/c this is being used to confirm something is what it's sold as. so what type of gemstone is it? it's def not topaz, spinel or sapphire, so l ike in my case if I buy something that's supposed to be Tanzanite and it barely registers as glass there's probably a. problem. None of the sapphires register as sapphire (though all others do easily).... they register more as topaz/ spinel.

I also tested all my loose unset stones from various sellers. All tested good, so its just this 1 pendant/ ring that seems to be the issue.
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
I have a Presidum and they are useful But with a BIG caveat.
Yes, it can ID any gems that are glass (CZ) or synthetic Quartz (like CZ). They can ID between amethyst and purple sapphire / spinel, they can ID between garnet and ruby or spinel, ID between citrine and yellow sapphire, ID Jadeite from quartz or glass BUT they can’t ID lab grown corundum or spinel from natural material. They also can’t detect any treatments ie flux filling or BE treatment.
The most common Issue, dare I say deception, is selling lab grown corundum or Spinel as natural and a Presidum can’t distinguish between lab grown and natural ie dug out of the earth. And it matters, a natural sapphire might be $1,000 plus a carat whereas a lab sapphire is worth under $10.
Your best friend when assessing gemstones is a loupe.
Yes, you need to invest some time into understanding and recognising gemstones by colour and what inclusions to expect to find under magnification.
Lab grown material tends to be perfectly even in colour and without any inclusions. Natural material is most often imperfect.
Lab grown material, flame fusion, is grown in a way that creates lines called striae.
There is a range of other pieces of equipment that test other characteristics of gemstones and help determine if treatments have been applied. Highly treated “natural” gemstones aren’t worth much more than synthetic so it is important to know about treatments as well.
Yes you're correct. I tested my ruby which I suspect is flux filled even though it wasn't listed by the seller. It def tested as ruby. Most of my high dollar stones have papers so they were more as controls and I dont think the GIA reports, etc are wrong on them. But you're right it's important to recognize the treatments, b/c if it was something random like I bought second hand without papers that would be a concern that presidium wouldn't tell me.
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
You would do much better with a few simple tools and the book GEM Identification made Easy by Antoinette Matlins.

Or if you want to make your life even easier identifying gemstones buy the software:
Gemology Tools Professional https://www.gemologytools.com/index.html

With this program you enter what you know about the gem such as it's color, transparency, single or double refractive etc. and the program narrows down what the gem could be.

If you have a Dichroscope, Loupe, Chesea filter and add a refractometer, you can pretty much identify almost anything.
I need to get this now to confirm the tanzanite I guess... I think the seller possibly mislabeled it. It's also a bright blue and most tanzanite I see is a distinctive purplish color.
 

Rfisher

Ideal_Rock
Premium
Joined
Oct 19, 2013
Messages
2,804
Oof.
Interesting.........
Whatever way this pans out - I hope you come back and let us know what is up. Either way.
Because It’s going to be valuable info on the presidium tester - or the vendor.
Because it’s also not difficult to guess what pieces this is about.
I doubt it’s nefarious.

And I hope it works out in whatever way that can keep a smile on your face when you see the pieces.

Edited to add:
I know some people get creeped out by remembering other posters project details and pieces from previous threads.
So - sorry if I’ve creeped you out :lol:
 
Last edited:

Bron357

Ideal_Rock
Premium
Joined
Jan 22, 2014
Messages
4,717
Did you clean the gemstones In question with rubbing alcohol before testing? If there is any “film” on the gemstones it can affect the result using a Presidum.
Spinel and Corundum do “overlap” on the Presidum. Though any stone testing as “glass” is a concern.
The majority of jewellers buy their melee in bulk from vendors they consider reliable and reputable but there’s always a chance that something else “gets” into the parcel. With melee size gems it’s unlikely that the jeweller would test them individually prior to setting.
 

Skyjems

Shiny_Rock
Trade
Joined
Jul 9, 2020
Messages
154
The presidium gem tester is not considered to be very accurate. You don't see serious gemologist using them. If I was to own just one tool it would be a refractometer.
+1 on this

It's a fun toy, but not for serious use. At most, you have a couple of pieces that are in the category 'require further testing'

Enjoy and good luck
 

arkieb1

Ideal_Rock
Premium
Joined
May 11, 2012
Messages
9,688
I use the machine first as a basic test, and then use a scope and a lab in Sydney (Australia) as the next step. I see it merely as a basic tool nothing more nothing less.
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
I use the machine first as a basic test, and then use a scope and a lab in Sydney (Australia) as the next step. I see it merely as a basic tool nothing more nothing less.
right, that's pretty much EXACTLY what I said I used it for: to verify things sold as X are in fact X not Y
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
Did you clean the gemstones In question with rubbing alcohol before testing? If there is any “film” on the gemstones it can affect the result using a Presidum.
Spinel and Corundum do “overlap” on the Presidum. Though any stone testing as “glass” is a concern.
The majority of jewellers buy their melee in bulk from vendors they consider reliable and reputable but there’s always a chance that something else “gets” into the parcel. With melee size gems it’s unlikely that the jeweller would test them individually prior to setting.
On the one I have (v2) they dont overlap. Topaz overlaps with both spinel and corundum but spinel ends where corundum begins.
the one blue sapphires in question I cant get to go past touching topaz.

I'm wondering if something in the setting possibly affects it?
I've tested the stones in question over and over and can not get them to read as what they were sold as.
Other rings I have and loose stones no problem. In all honesty though I think its a good success rate when it comes to buying gems online. I also tested some antique Scottish brooches I have and they checked out, which is nice.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
15,856
A word of warning - for the Presidum type II synthetic diamond tester.
About 1/3rd of Argyle diamonds (all colours to the best of my knowledge) will come up as refer.
If you get that many in a parcel you will think it has been seeded with fakes.
Seems more likely to happen with SI and lower clarity grades.
 

whimsicism

Rough_Rock
Joined
Jul 23, 2019
Messages
3
That's scary... and this may be an unpopular opinion here, but the fact that all your stones passed on the gem tester other than the stones from one particular vendor raises a red flag for me. I'd hate to think that there are problems with anyone's stones, but I'd definitely prefer to know if there are problems.

Thank you so much for sharing, and do update this thread when the test results are back.
 

Bonsai

Shiny_Rock
Joined
Oct 11, 2019
Messages
162
sorry for being MIA I just didnt check the forum and was busy. No I didnt really pursue it. While they dont measure what they were sold as they measure as "something". The blue sapphires (light blue) register as topaz most likely. I didnt see the point in making anything of it when they are 1 mm stones. But it does give me caution for the future. The tanzanite registers also but just not quite as tanzanite. The larger stones in the center of the 2 designs both register as sold as.

And in reality I had a frustrating experience with another seller (well known to this forum) b/c seller swore they would never make a ring 1mm thin. the purchase order is 2 mm wide and 2 mm thick. At no point in the band is it 2 mm thick. It's barely over 1 mm which is too thin for me. Seller basically said "oh well". So I didnt figure the other seller would really care if I pitched a fit over 1 mm stones. But in the future I will continue to thoroughly check what I buy


On a side note when I was in HS and ebay came out I bought little things: some sealed panda coins and white (clear) sapphires. I assumed by now they were all fakes given what has happened with the internet and things coming out of china. Turns out not only were the panda coins real, the sapphires registered as sapphires on the presidium tester. Now they could easily be man made but none the less... interesting.
 
Last edited:
Be a part of the community It's free, join today!
    Something Blue
    Something Blue
    November’s Jewels Of The Weeks
    November’s Jewels Of The Weeks
    Upgrade to Five-Stone
    Upgrade to Five-Stone

Need Something Special?

Get a quote from multiple trusted and vetted jewelers.

Holloway Cut Advisor



Diamond Eye Candy

Click to view full-size image.

New posts

Top