Interesting PMV puzzle for a 0.999 fine 1 oz silver bar

astrorat

At one of my local B&M shops I picked up an uncommon 1 oz 0.999 fine silver bar labeled "Interad Systems, Inc." with s/n 000090. A brief Internet search did not yield any results as to its origin.

As part of my routine with bullion, I did some testing at home.

Using the Sigma Metalytics PMV is quick and easy, especially with 1 oz silver bars of the "standard" size (nominal 50 x 29 x 2.5 mm). I was surprised, when the display on the PMV for 0.999 silver was an arrow to the far right, indicating it is likely the wrong metal. Testing with the main sensor (imaged below) on a setting for 0.925 silver brought the reading closer to the target range. The bar has "high relief" areas, so that may affect the results a bit. Maybe it's sterling, but labeled 0.999?

I tried the large wand and got the same results for 0.999 silver and 0.925 silver. When I tried the small wand and placed the wand over the "flat" areas of the bar, the result was in the target range for sterling silver. Interesting.

So, the next step was to do specific gravity testing ... and this is where the result becomes puzzling. Replicated testing gave the same result. Namely, the bar has the specific gravity of pure silver (SG 10.51) and not the lower specific gravity of sterling silver (SG 10.36).

The PMV was just updated and recalibrated ... and I am familiar with its use. My balance is a high-quality analytical balance (+/- 0.1 mg) and is calibrated correctly. I also have a PhD in the pharmaceutical sciences ... so it's not experimental error.

I am going to send this puzzle to the good folks at Sigma Metalytics as well.

Any thoughts as to what might be causing the odd results? Since the PMV is based on resistivity, are there known contaminants in "old bars" that would change the resistivity so much that 0.999 silver would read as if it's sterling? Although not an inorganic chemist, I find this quite interesting.

Below are images of the bar on the main sensor. The reading is the same (for 0.999 silver or 0.925 silver) regardless if testing the obverse or reverse of the bar.

ricko

That is a puzzle... You are more technically competent than I and the results are confusing. Please let us know what you discover - either from further testing or what Sigma may tell you. Cheers, RickO

derryb

looks like it might be 90% Try the 90%US setting.

astrorat

@derryb said:
looks like it might be 90% Try the 90%US setting.

If it was made of 90%, the SG would be even lower at around 10.31.

I have little doubt it's 0.999 silver, I am just curious as to what is causing the resistivity to be off.

astrorat

Surprisingly ... I received a response from Sigma Metalytics on a Saturday!

"The reading you are getting is not consistent with pure silver. It could be there are trace contaminants in the bar, such as lead or iron, that cause the resistivity of the bar to be higher than anticipated, but still with a high silver content. Without assaying the bar there is little more that can be determined."

So it looks like the "trace contaminant" theory may be on target. I do not know enough about metal chemistry to know at what level of contamination would lead the resistivity of 0.999 silver to read as sterling, but it may be low enough that it would "pass" quality control for smaller refineries in the 1970s and/or 1980s. My testing of Engelhard bars from the 1970s and 1980s are spot on (no pun intended) for 0.999 fine silver.

Now I am on a mission to do more specific gravity testing on some bars and rounds. Fun with metal!

derryb

just out of curiosity, try 90% on the PMV

astrorat

@derryb will do ...

For "pre-1900," "pre-1945" and "1960" coin silver ... the PMV reads in range ... just as it did for 0.925 sterling silver.

So, without any additional testing, the PMV would lead one to believe the bar could be the same composition as US 90% silver coins or sterling silver.

derryb

Your earlier pic shows .925 reading to be slightly out of range. That is why I suggested a 90% reading. Where does the bar fall between the brackets at 90%. Likely dead on or next to dead on. Flip the bar over and read it a second time. Your contaminants, according to your SGT, are not evenly dissolved and have rendered your .999 product into a .90 product. Keep in mind that contaminants are usually intentional when creating anything less than .999 silver product.

I suspect the PMV is giving you an accurate reading at 90%, your SGT is not, and that your bar is incorrectly marked as .999.

astrorat

Since the bar has reasonably high relief, the reading from the main sensor is affected slightly. When using the small wand and placing the wand on a flat area without relief, the reading for 0.925 is near the center. The reading for 90% is just to the left of center.

Irrespective of the PMV resistivity testing ... the specific gravity of the bar does not support the composition of sterling or 90%. The specific gravity test is dead on for 0.999.

derryb

High relief should not matter. I get accurate readings on bullion coins in a slab, same reading that I get for the same coin not in a slab. Different wands will give different readings and you have to develop a knack for which to use with which size product. With your bar I would rely on the third, large wand. This wand is optional with PMVs, most come with only the small and the intermediate wand. If you don't have the third, large wand then rely on the use of no wands with 1 oz. or larger products.

Based on your test results it sounds like you have a .999 plated 90% bar, or something is off with the SGT. Keep in mind the PMV is designed to read past any plating, thus it's value when checking plated items. I doubt that anyone would go to the trouble to plate a one ounce 90% bar with .999 silver but you never know.

Research shows that INTERAD was an advertising agency based in Illinois.

astrorat

According to the PMV manual, high relief does play a role. I do have the bullion wand and using it (along with the calibration disk) gives me the same results.

I appreciate your thoughts on being a plated bar. The SG testing is accurate (and has been "triple" checked). Without assaying the piece, we may never know definitively or what "contaminants" are present.

asheland

Interesting thread! Can you perhaps take it to someone with an X-ray gun? That would give you a definite answer.

astrorat

I have contacted an inorganic chemist I know at the university to see if he has instruments that can do non-destructive testing.

I found a couple of other silver bars from different manufacturers that gave the same type of readings. This is interesting.

Weiss

I don't know if it was mentioned, but did you try the 99.99% setting?

astrorat

@Weiss said:
I don't know if it was mentioned, but did you try the 99.99% setting?

Yes ... I checked and the result was the arrow far to the right.

astrorat

I decided to do a quick qualitative test. I have a neodymium magnet ramp I made as a quick visual test. The Interad bar slides slightly faster than both a Engelhard and Johnson Matthey bars I know to be pure silver.

Another bar that is giving me the same type of results is a 1 oz bar from Deak-Perera. Same PMV readings as the Interad bar with an SG that is on target for pure silver. And it also slides down slightly faster than the Engelhard or JM bar.

astrorat

I need to go to my local B&M and buy a sterling bar as a control.

derryb

Maybe you're update to the PMV is causing problems.

astrorat

@derryb said:
Maybe you're update to the PMV is causing problems.

Well that certainly is possible. I would hope not, but it's possible.

Pokermandude

Looks like a combination of the bar relief and maybe some shoddy/impure silver used in the making of that bar is the culprit.

derryb

@Pokermandude said:
Looks like a combination of the bar relief and maybe some shoddy/impure silver used in the making of that bar is the culprit.

relief or raised surfaces don't affect the PMV. It can verify through a slab.

Smudge

How does it compare with a 90% coin on the magnet slide?

1630Boston

Just curious, did you try it with the small wand and the calibration disc?

1630Boston

I could find absolutely nothing online about the bar [yet] but here is the business in its current condition
1100 Remmington Rd, Shaumburg, Illinois.

And Interad Systems had a US Patent granted in 1984

Housing for an ionization detector array in a tomographic scanner
United States of America Patent
PATENT NO 4490614
SERIAL NO
06373431

Stats
Dec 25, 1984 Grant Date
app pub date Apr 30, 1982
filing date Apr 30, 1982
Expired
)

MyWorldCoinTypeSet

Namely, the bar has the specific gravity of pure silver (SG 10.51) and not the lower specific gravity of sterling silver (SG 10.36).

Not my area of expertise, but the 10.36 SG of sterling silver assumes the 7.5% "other" metal is copper. If the 92.5% silver is alloyed with a mix of a heavier metals like lead or molybdenum, the SG would be higher.

shinywhite

@astrorat said:
At one of my local B&M shops I picked up an uncommon 1 oz 0.999 fine silver bar labeled "Interad Systems, Inc." with s/n 000090. A brief Internet search did not yield any results as to its origin.

As part of my routine with bullion, I did some testing at home.

Using the Sigma Metalytics PMV is quick and easy, especially with 1 oz silver bars of the "standard" size (nominal 50 x 29 x 2.5 mm). I was surprised, when the display on the PMV for 0.999 silver was an arrow to the far right, indicating it is likely the wrong metal. Testing with the main sensor (imaged below) on a setting for 0.925 silver brought the reading closer to the target range. The bar has "high relief" areas, so that may affect the results a bit. Maybe it's sterling, but labeled 0.999?

I tried the large wand and got the same results for 0.999 silver and 0.925 silver. When I tried the small wand and placed the wand over the "flat" areas of the bar, the result was in the target range for sterling silver. Interesting.

So, the next step was to do specific gravity testing ... and this is where the result becomes puzzling. Replicated testing gave the same result. Namely, the bar has the specific gravity of pure silver (SG 10.51) and not the lower specific gravity of sterling silver (SG 10.36).

The PMV was just updated and recalibrated ... and I am familiar with its use. My balance is a high-quality analytical balance (+/- 0.1 mg) and is calibrated correctly. I also have a PhD in the pharmaceutical sciences ... so it's not experimental error.

I am going to send this puzzle to the good folks at Sigma Metalytics as well.

Any thoughts as to what might be causing the odd results? Since the PMV is based on resistivity, are there known contaminants in "old bars" that would change the resistivity so much that 0.999 silver would read as if it's sterling? Although not an inorganic chemist, I find this quite interesting.

Below are images of the bar on the main sensor. The reading is the same (for 0.999 silver or 0.925 silver) regardless if testing the obverse or reverse of the bar.

The reading shows the bar reading outside of the sterling silver results. Though you mentioned you tested for 90% silver. My understanding that if the other metals used in the bar is indeed copper, then the slide tests should yield a slower result than mentioned bc copper has a stronger reaction to the magnets than silver, although both silver, and copper are dia-magnetic. Copper is also para magnetic, just slightly

Pokermandude

@derryb said:

@Pokermandude said:
Looks like a combination of the bar relief and maybe some shoddy/impure silver used in the making of that bar is the culprit.

relief or raised surfaces don't affect the PMV. It can verify through a slab.

Relief/raised surfaces do indeed affect the PMV reading. The PMV does read right through the slab, as if it is not there. But uneven surfaces of the metal sample will absolutely affect the reading.

https://sigmametalytics.com/instructions/pmv-pro-videos.html

On the "Working with silver bars" video, they mention and show the PMV reading being different using the flatter side of the bar, vs the "relief" side of the bar.

1630Boston

@1630Boston said:
Just curious, did you try it with the small wand and the calibration disc?

I'm curious if you tried it with the calibration disc below the bar ?

Jinx86

Know anyone with an XRF? We have one at our shop, it's quite useful. Might not be worth it for one bar though.

astrorat

@1630Boston said:

@1630Boston said:
Just curious, did you try it with the small wand and the calibration disc?

I'm curious if you tried it with the calibration disc below the bar ?

LOL ... I don't remember. Heck! That was over 6 months ago!

1630Boston

@astrorat said:

@1630Boston said:

@1630Boston said:
Just curious, did you try it with the small wand and the calibration disc?

I'm curious if you tried it with the calibration disc below the bar ?

LOL ... I don't remember. Heck! That was over 6 months ago!

Sorry, I need to pay more attention to dates

CaptHenway

I am a great believer in Specific Gravity.

1630Boston

@CaptHenway said:
I am a great believer in Specific Gravity.

Me also,
I supervise SG tests every day, not on coins but SG tests combined with other available information yields results that cannot be disputed. JMO