Sigma precious Metal Verifier

[stataman]

What do people think of the Sigma precious metals verifiers? Worth buying and how accurate? Any surprises with tungsten filled gold bars? there appear to be many fake pamp and perth mint gold bars when you scan facebook and see them being sold way below spot.

[paulmerton]

My thoughts? They're expensive, and I would not trust the results on their own. Always carry out other tests in addition to using the sigma verifier, as it's entirely feasible for someone to make a counterfeit bar that fools the device, but much harder to make a counterfeit that passes every test. For that reason, I would never trust a sealed bar to be what this device claims it is without also opening the packaging to test the weight, dimensions, etc. (unless it's from a reputable source, like direct from the Royal Mint).

That said, they're a good addition to the average person's test suite (unless you can afford an XRF tester!)

As a case in point, here's one example of why you shouldn't have blind faith in the output without also doing other tests:

[LawrenceChard]

1 hour ago, paulmerton said:

My thoughts? They're expensive, and I would not trust the results on their own. Always carry out other tests in addition to using the sigma verifier, as it's entirely feasible for someone to make a counterfeit bar that fools the device, but much harder to make a counterfeit that passes every test. For that reason, I would never trust a sealed bar to be what this device claims it is without also opening the packaging to test the weight, dimensions, etc. (unless it's from a reputable source, like direct from the Royal Mint).

That said, they're a good addition to the average person's test suite (unless you can afford an XRF tester!)

As a case in point, here's one example of why you shouldn't have blind faith in the output without also doing other tests:

That's a good demo.

Would it be worth adding a brief summary and explanation, to make it idiot proof?

😎

[LawrenceChard]

2 hours ago, stataman said:

What do people think of the Sigma precious metals verifiers? Worth buying and how accurate? Any surprises with tungsten filled gold bars? there appear to be many fake pamp and perth mint gold bars when you scan facebook and see them being sold way below spot.

Most people who own one seem to think they are wonderful, although it might be like owning a new car.  Presumably it does what you bought it for, and if their are faults with it, you don't want to admit you bought the wrong car.

The fact that we have an XRF machine may help to answer your question, but as we have never owned or used a Sigma, perhaps we are missing something.

Accordingly, we have ordered one of each of the three Sigma models, all fully loaded with all accessories, primarily for evaluation. Two should arrive in about a month, but the mini version will be delayed longer.

Once we receive them we intend to evaluate them, and share our experiences and thoughts, in a review on our website, and here.

After that, we will probably become a UK distributor, unless our evaluation persuades us otherwise.

🙂

[paulmerton]

3 minutes ago, LawrenceChard said:

That's a good demo.

Would it be worth adding a brief summary and explanation, to make it idiot proof?

😎

Sure. You have to tell the device what metal you're expecting. When you place the metal on the sensor, it shows the output on the display.

If the box appears within the brackets, then it's deemed to be within an acceptable range. If it's just outside, then further investigation is needed. If it's well out (an arrow appears instead of a box) then it's definitely not the right metal.

So I see it as a device for confirming some things are definitely fake, rather than confirming things are real. So it is quite useful as a quick and reliable way of weeding out some (but not all) fakes.

As far as I understand, the device measures the resistivity of the metal and compares it with the expected resistivity. This means it cannot be fooled by a silver plated copper bar if you're checking for 999 silver, but evidently it thinks pure copper has exactly the same reading as sterling silver (not something I expected!)

It should detect a gold bar with tungsten inserts as fake. There is a separate "bullion wand" you can plug into it for deeper penetration (ooer), but for 1oz coins you can just slap them on the middle.

[Stu]

4 hours ago, LawrenceChard said:

Most people who own one seem to think they are wonderful, although it might be like owning a new car.  Presumably it does what you bought it for, and if their are faults with it, you don't want to admit you bought the wrong car.

The fact that we have an XRF machine may help to answer your question, but as we have never owned or used a Sigma, perhaps we are missing something.

Accordingly, we have ordered one of each of the three Sigma models, all fully loaded with all accessories, primarily for evaluation. Two should arrive in about a month, but the mini version will be delayed longer.

Once we receive them we intend to evaluate them, and share our experiences and thoughts, in a review on our website, and here.

After that, we will probably become a UK distributor, unless our evaluation persuades us otherwise.

🙂

It will be interesting to read your findings, I’m sure they will be impartial..  

[Chrisplym]

@LawrenceChard I will also be interested in reading the outcome of your review as I have been thinking about buying one of these for ages.

[LawrenceChard]

5 hours ago, Stu said:

It will be interesting to read your findings, I’m sure they will be impartial..  

Depends how much discount they give us!

(Only joking!)

😎

[ArgentSmith]

@paulmerton is 100% correct with both his posts. In particular trying to verify silver below .999 is dubious due to similar conductive properties silver has with copper, parameters for Sterling, Britannia, 90% etc are set to allow for different alloys and are too wide and forgiving. 

All metals when testing for 999 or better are obviously calibrated with tight parameters which makes it an excellent tool for non destructive testing.

[LawrenceChard]

12 hours ago, paulmerton said:

Sure. You have to tell the device what metal you're expecting. When you place the metal on the sensor, it shows the output on the display.

If the box appears within the brackets, then it's deemed to be within an acceptable range. If it's just outside, then further investigation is needed. If it's well out (an arrow appears instead of a box) then it's definitely not the right metal.

So I see it as a device for confirming some things are definitely fake, rather than confirming things are real. So it is quite useful as a quick and reliable way of weeding out some (but not all) fakes.

As far as I understand, the device measures the resistivity of the metal and compares it with the expected resistivity. This means it cannot be fooled by a silver plated copper bar if you're checking for 999 silver, but evidently it thinks pure copper has exactly the same reading as sterling silver (not something I expected!)

It should detect a gold bar with tungsten inserts as fake. There is a separate "bullion wand" you can plug into it for deeper penetration (ooer), but for 1oz coins you can just slap them on the middle.

 

7 hours ago, Chrisplym said:

@LawrenceChard I will also be interested in reading the outcome of your review as I have been thinking about buying one of these for ages.

I think that @paulmerton's will be a good guide.

I tried to work out how they work, which is not clear from some of their online documentation. There was some mention of electrical resistivity, but then also something about eddy currents.

The fact you need to tell it what you are trying to test is rather quirky, but they are much cheaper than an XRF machine.

 

[paulmerton]

47 minutes ago, LawrenceChard said:

The fact you need to tell it what you are trying to test is rather quirky

That is the most obvious limitation of the device (at least the version shown above), and is most likely unavoidable due to the way it works.

An XRF machine will tell you that a sterling silver crown contains 92.5% silver (give or take), regardless of what the remaining 7.5% is made up of.

As the Sigma verifier only checks whether the test sample as a whole has the same resistivity as a particular composition of sterling silver, it's not great for checking older crowns that also contain 92.5% silver but have completely different proportions of other metals in the alloy (not just copper). The composition of the remaining 7.5% can really throw the Sigma off the scent, even though the coin still contains the right amount of silver.

There are no such problems with using the Sigma device to test pure silver, gold, platinum and palladium, as the amount of other metals is so low that it is unlikely to influence the resistivity.

However! If you were to alloy a high resistivity metal with a low resistivity metal in the right proportions, I believe you could create a metal that the device believes is pure silver/gold/whatever. The fake sample would be unlikely to have the correct density and other properties of the genuine metal, though, which is why the other tests are still essential in my view. The higher end Sigma device can also check the density for you I believe.

That's my understanding of how it works, anyway.

 

Edited April 26, 2022 by paulmerton
spurious if

[paulmerton]

Some more sterling silver examples that demonstrate just how inconsistent their compositions must be...

A 2012 sterling silver crown, just about within the acceptable range (note that you don't have to remove the coin from the capsule, and the results are instant, so that's nice):

Another modern-ish one still in range:

An older one, out of range!

An even older one, even more out of range:

But if you change the search parameters to US 90% silver, you get a "good" result. This "hack" turns out to be suitable for helping verify most genuine crowns from 1800-1900 or thereabouts (obviously it doesn't mean they are 90% silver though):

Just to show the machine actually works, here's a cupronickel 50 pence coin being tested as sterling silver:

And here's the same 50p in 90% US silver mode - still well out:

And here's some 999 silver giving the expected result:

If anything, this shows how inconsistent the composition of sterling silver must be over the years, as well as how useless such a device is for testing it. I'd be interested if you do the same thing with an XRF tester at Chards (or have you done such a thing already?!)

[stataman]

I guess I'm not too worried about verifying old crowns. My main fear is modern 999/9999 silver and gold bars and the sigma should be good at that it seems. 

[paulmerton]

1 minute ago, stataman said:

I guess I'm not too worried about verifying old crowns. My main fear is modern 999/9999 silver and gold bars and the sigma should be good at that it seems. 

Aside from the caveat I just pointed out.  It can be fooled, but in conjunction with other tests you'd be hard to fool.

[James32]

There is also another way to use the sigma, not that ive ever found the need.

https://youtu.be/ltTnCOeqtY4

[paulmerton]

2 minutes ago, James32 said:

There is also another way to use the sigma, not that ive ever found the need.

https://youtu.be/ltTnCOeqtY4

This is also in the instruction book if anyone reads the whole thing  

[James32]

Just now, paulmerton said:

This is also in the instruction book if anyone reads the whole thing  

If you sat and read the instruction book before playing with machine then you need help 🤣🤣

[paulmerton]

1 minute ago, James32 said:

If you sat and read the instruction book before playing with machine then you need help 🤣🤣

Cheeky 😛

I actually had over a week to download the manual in PDF format and read it before the device had even made its way to the UK.

[paulmerton]

Topically, the manual includes the following warning on the last page:

Use with caution:

It is not our recommendation or intention for the Precious Metal Verifier (PMV) to be the sole means for identification of counterfeit coins and bars. Our measurement of a material’s electrical characteristic (resistivity or conductivity) is necessary, but not by itself sufficient for such a purpose.

We recommend that you check the item being measured against its specified weight, and size along with the resistivity measurement. You should use your normal visual checks of the material as well.

Other materials have the same resistivity as pure gold, and as such can look like gold on the PMV. These materials will be less dense than gold, so they will be larger or weigh less than the specified value. If you check material that looks good on the PMV, but has the wrong weight or dimensions, then you should not accept the material as consistent with the correct metal.

Do not try to use the PMV to determine what a material is. The PMV will only provide the electrical characteristic (resistivity or conductivity) of the metal, not the atomic structure. Correct use is to have an expectation of the material type (gold, silver, platinum, etc.), and alloy content (22K, coin silver, sterling, .999 pure, etc.), and to verify that the material being tested is consistent with your expectation.

Used in this way, the PMV is a great asset in avoiding counterfeit products.

 

And another interesting bit from the technical white paper:

The PMV tests a metals resistivity. Gold has a higher resistivity than copper, but lower than zinc or tin. So, unlike silver, there are combinations of alloys that can have the same resistivity as gold.

When readings are uncertain, be advised to measure the items thickness and diameter. Weigh the sample and make sure the weight and dimension match the expected value. If a counterfeit sample matches the resistivity of gold, its weight and/or dimensions will usually be off by more than a factor of two.

Tungsten has practically the same specific gravity as gold, this means that for a given volume tungsten and gold can have the same weight. Gold bars have been counterfeited by covering tungsten under a gold clad surface. This was a main reason for the development of the PMV Bullion wand. Most tungsten samples, within the depth limit of the sensor used, will be rejected by the PMV as they have a much higher resistivity than gold.

[James32]

1 minute ago, paulmerton said:

Cheeky 😛

I actually had over a week to download the manual in PDF format and read it before the device had even made its way to the UK.

Yeah I watched video after video whilst waiting, still had to read the book though as I went lol.

I only use as the last port of call and mainly.999 material ( manufacturers dimensions with calipers, magnet,weight etc,) then and only then does it reach the sigma and I do both varieties ( just machine then wand on everything )

I've tried to fool it when say testing a tube of coins, test 5 then slip a 50p in every so often but it picks up on it thankfully. I'm glad I bought it and would recommend whole heartedly, but advise like yourself to only use in conjunction with other methods ( otherwise bad habits kick in and if machine has a bad day,we all have a bad day)

[CANV]

 

the pro for example measures 13 onwards silver Brits as thin and on the margin of green n yellow 

this is because it measures. (or attempts to) the whole surface area. not the rim which is of course thicker. 

green is 9999. yellow 999. its set up for extra sensitivity on silver coins 

[Paul]

Out of interest what the UK RRP in GBP £ for one of these Sigma machines ?? 

[ady]

1 hour ago, Paul said:

Out of interest what the UK RRP in GBP £ for one of these Sigma machines ??

Depends on the model, the one above is high range. i got a mid range one from Zetberg, if you look at the site you will buy in Euro. Obviously do the exchange rate, but you will pay vat on import. Happy with mine as confirmed a few fakes I was always dubious about.

[GoldDiggerDave]

1 hour ago, Paul said:

Out of interest what the UK RRP in GBP £ for one of these Sigma machines ?? 

I did get a quote for a Nitron DXL XRF machine 15.2k plus VAT    

[GoldDiggerDave]

@Paul I looked around at the sigma machines a while ago the pro model was around 2.3k  but this was from America so would be more after import costs.