Sigma Precious Metals Verifier... What does it tell us when the marker is not in the box?

[arphethean]

Last night I was sorting through a parcel of silver crowns that came in and testing them on my Sigma. I came across this 1972 Elizabeth and Philip crown

Initially I put this it aside as "not silver" as it tested way out of the box whereas all the other sterling silver coins had the marker well inside the box, as did my Victoria jubilee crown.

   

1972 "Sterling Silver??" crown, 1889 sterling silver crown, 1977 sterling silver crown, CuNi crown

I noted that the COA mentioned the same coin was made in CuNi and Silver and just thought the seller must have mistook this as a silver one.

However I went back to check it and noted that the weight, diameter and thickness matches the silver crowns. I also did a magnet test and the magnet slid slowly down the coins like with the sterling coins. 

Above: On the left, the 1972 "Sterling Silver??" crown, on the right, 1977 sterling silver crown

 

 

Above: on the left, 1977 sterling silver crown;  on the right, CuNi crown

 

So in dimensions it matches a genuine silver crown but the Sigma shows it has higher resistivity (999 silver (lower resistivity)shows the marker to the left, whereas Cuni (higher resistivity)has it way off to the right).

So what is the Sigma telling me about this coin here? Is the composition of Sterling slightly different, perhaps with a more resistive metal in place of some of the copper but with the same 925 silver content??

Does anyone with a better understanding of the Sigma's operation and coin metal compositions know what's going on here?

Edited January 4, 2023 by arphethean

[Orpster]

Try it on an 80% silver scan

[arphethean]

Interesting...

Does this mean the silver content is a bit out?

[BackyardBullion]

This highlights nothing more than the machine is finely calibrated for certain coins and types and fails on others. 

The sigma is not a fail proof test by a long way and those that rely on this ALONE to certify silver are playing with fire in my opinion.

As a tool to identify if further and more extensive tests are needed, its perfect. 

This is that case. 

[Orpster]

3 minutes ago, arphethean said:

Interesting...

Does this mean the silver content is a bit out?

Seen this before on commemorative crowns, sometimes if you move the coin around the reading also changes so it may be the sigma is just reading a spot with less silver, or maybe if it gives a consistent read the wrong ratio's were used?
It shows it is a silver coin not a Cupro though, so I guess a win for the Sigma  

[BackyardBullion]

1 minute ago, Orpster said:

Seen this before on commemorative crowns, sometimes if you move the coin around the reading also changes so it may be the sigma is just reading a spot with less silver, or maybe if it gives a consistent read the wrong ratio's were used?
It shows it is a silver coin not a Cupro though, so I guess a win for the Sigma  

Not necessarily true. 

A must watch for any sigma users that think its infallible 

 

[arphethean]

3 minutes ago, BackyardBullion said:

Not necessarily true. 

A must watch for any sigma users that think its infallible 

 

Yep. I know it's not infallible - I have had a few inconsistencies before so just wanting to explore the issue a bit with a case in point

[James32]

44 minutes ago, arphethean said:

Yep. I know it's not infallible - I have had a few inconsistencies before so just wanting to explore the issue a bit with a case in point

From my own personal experience...

The cupronickle crown are almost identical in size, but the thickness is bigger ( as your photograph proves)

Sigma is excellent on modern bullion, specifically  .999 or higher but can sometimes struggle with older coins of less purity.

Obviously it's been calibrated to check certain assumed mixes of alloys, but as every mint changed recipes a few times over the years this can lead to inconsistent readings. Shape of coin ( if its raised and not making enough contact with the testing surface) and grime can play a part too.

The fact you still had a solid bar although outside the target area, would has told me there's an issue but not a critical one. I would have lowered the settings to 80% like @Orpster recommended and then done all the Manuel tests you obviously did. Have you tried the wands on it? Could simply be reading a part of the coin that's got a lower content. 

 

Edited January 4, 2023 by James32

[ZigZag]

3 minutes ago, James32 said:

From my own personal experience...

The cupronickle crown are almost identical in size, but the thickness is bigger ( as your photograph proves)

Sigma is excellent on modern bullion, specifically  .999 or higher but can sometimes struggle with older coins of less purity.

Obviously it's been calibrated to check certain assumed mixes of alloys, but as every mint changed recipes a few times over the years this can lead to inconsistent readings. Shape of coin ( if its raised and not making enough contact with the testing surface) and grime can play a part too.

The fact you still had a solid bar although outside the target area, would has told me there's an issue but not a critical one. I would have lowered the settings to 80% like @Orpster recommended and then done all the Manuel tests you obviously did. Have you tried the wands on it? Could simply be reading a part of the coin that's got a lower content. 

 

Everything you have just said is why I decided to stick with boring modern Bullion. 

My Sigma Pro has detected 2 fakes of my own and 3 for someone else, all Silver 1 Oz versions and not more than 30 years old. I’m yet to detect any inconsistencies with anything gold but feel confident the likes of “main” mint coins would show with my current version.

It’s the limitations which keep me from being too adventurous but that’s fine for me, I’m not a true numismatic collector, just a boring stacker, with odd bits of variety thrown in. Which case the Sigma does the job.

[James32]

43 minutes ago, ZigZag said:

Everything you have just said is why I decided to stick with boring modern Bullion. 

My Sigma Pro has detected 2 fakes of my own and 3 for someone else, all Silver 1 Oz versions and not more than 30 years old. I’m yet to detect any inconsistencies with anything gold but feel confident the likes of “main” mint coins would show with my current version.

It’s the limitations which keep me from being too adventurous but that’s fine for me, I’m not a true numismatic collector, just a boring stacker, with odd bits of variety thrown in. Which case the Sigma does the job.

Me too generally, although I do all the Manual tests first, then and only then does an item reach the sigma. But like you say for modern stuff it's excellent and obviously what it was in large part designed for considering when it came out.

Edited January 5, 2023 by James32
Worms on my keyboard

[BackyardBullion]

3 minutes ago, James32 said:

although I do all the Manuel tests first

[Anteater]

3 minutes ago, James32 said:

I do all the Manuel tests first

Test result: "Is hamster".

[BackyardBullion]

2 minutes ago, Anteater said:

Test result: "Is hamster".

Beat you to it!

Great minds!

[Anteater]

5 minutes ago, BackyardBullion said:

Beat you to it!

Great minds!

I knew I shouldn't have bothered correcting that typo...

[iacabu]

@arphethean which model Sigma are you using?