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Introduction

The Precious Metal Verifier is a device manufactured by Sigma Metalytics in Chico, California that uses electromagnetic waves to assess the metal in coins and bullion.  The device measures the resistivity of the bulk metal, penetrating below the thin plating used on most counterfeit coins and bars, and compares the result to a range of values compiled from measuring known authentic samples.  A result falling within the range of known values confirms that the electrical properties of the item being tested match what is expected for that metal.  A result falling outside the range of known values suggests the bulk metal in the coin or bar is not what it claims to be.

The PMV is completely non-destructive and can test coins and bullion through common packaging like coin flips and zip bags.  In the case of larger coins (roughly 1/2 ounce and up) the PMV can even read through numismatic slabs.  The built-in rechargeable battery makes the device very portable and it can be connected to a PC to update the reference database as the manufacturer makes improvements and adds new alloys to the testing options.

PMV Main UnitPMV Main Unit

Sensors and Wands

The main PMV device has a built-in sensor appropriate for 1 ounce and larger coins and bars, including those sealed in numismatic slabs.  Optional sensor wands expand the testing capabilities to bare fractional bars and coins as small as 1 gram, and to slabbed coins approximately 1/4 ounce and larger.  The Basic Kit includes the small and large wands.  The Bullion Kit includes a third "bullion wand" that penetrates much deeper into the metal than the other wands, making it useful for larger bullion items and poured bars that have deeper surface textures and stamping than typical minted coins and bars.  The bullion wand can also better distinguish between copper and silver using a special range that is twice as sensitive as the other sensors.

PMV WandsPMV Wands

Using the appropriate sensor is critical to producing accurate results.  The PMV user manual includes a sensor selection chart that covers metal type, diameter/width, and thickness.  The item being tested must cover the entire face of the sensor for an accurate reading.  For the main sensor built into the PMV unit, this means covering the dark circle printed around the sensor.  For the wands, it means covering the entire face of the wand.  If the item being tested is encased in a numismatic slab, then it must be slightly larger than the face of the sensor (the dark circle for the main sensor, and the face of the wand for the Large Wand).  The Small Wand cannot read through numismatic slabs. 

In addition to ensuring the face of the item being tested is large enough to completely cover the sensor, the thickness is also important.  Very thin samples must be backed with the included calibration disk to get an accurate reading.  The exact thickness that requires use of the calibration disk depends on the metal being tested.  It is especially important to consult the chart for platinum, palladium, and gold alloys.  They have higher resistivities than pure gold and silver so the PMV penetrates deeper into the metal.  Using the wrong sensor could mean measuring all the way through the coin, resulting in a false reading.  It is a good idea to consult the sensor selection chart when testing any item under 1 ounce.

PMV Sensor Selection Chart

Basic Use

In most cases testing a coin or bullion item only takes a few seconds.

  1. Remove any items from the main sensor area, and if using a wand, move the wand away from any metal objects.
  2. Power on unit.  If using a wand, connect it now.  A light will indicate whether the main sensor or wand is currently selected.  To switch between the main sensor and wand, press the SENSOR button.
  3. Press the RUN/CAL button to calibrate the device.  This is required whenever turning the unit on, changing sensors, or changing metals.
  4. Use the up and down arrows to select the metal category (Gold, Silver, Other).
  5. Use the left and right arrow keys to select the specific metal or alloy within the category (Pure Gold, American Eagle Gold, etc.)
  6. Press the RUN/CAL button, again with no metal items on or near the sensors.  The display will show the selected metal and the status will change to "Ready: Place Sample"
  7. Place the sample on the main sensor, or move the wand to the sample.
  8. The PMV will display the result on the screen.
  9. Remove the item and place another of the same metal on the sensor, or start at step #4 to test a different metal.

PMV Testing Counterfeit Perth BarPMV results for a counterfeit Perth Mint gold bar in assay card.

Results

The PMV displays the measurement visually rather than numerically, using a black box on a spectrum.  The brackets indicate a range of expected values compiled from testing numerous known authentic examples of the metal or alloy selected.  The black box shows where the item you are testing falls in that range.  If the box falls inside the brackets, the value measured is within the expected range.

PMV ScreenPMV display showing a result that falls within the expected range.

If the box falls outside of the brackets, more analysis is needed.  If the box falls to the left of the brackets, the item being tested is less resistive than expected.  Since silver is the most conductive metal, nothing should ever fall to the left of the brackets when the PMV is set to test pure silver.  However, in the case of testing a less conductive metal like gold, an item made of silver or copper could fall outside of the brackets to the left.  More common with counterfeit items is falling outside of the brackets to the right.  This means the item is more resistive (less conductive) than expected, suggesting the metal is less pure than indicated, contains impurities, or is a different metal altogether.

PMV Screen 2
PMV Screen 3PMV displays showing results falling outside the expected range.

Any item that falls outside of the brackets, but close to the brackets, warrants further testing. 

A result that falls too far outside the expected range to plot on the display will instead show an arrow.  Again this will usually be to the right, indicating a much more resistive (less conductive) metal.  This is the typical behavior for most counterfeit silver items, which are typically made from brass with a thin silver plating.

PMV Screen 4
PMV display showing a result that falls far outside the expected range.

If the PMV does not display a result after placing the item on the sensor, but instead "resets" back to the RUN/CAL screen, this is an indication that the item is ferrous (contains iron) or magnetic.  The PMV cannot take a measurement on ferrous or magnetic items, but obviously any ferrous or magnetic item claiming to be a precious metal item is a counterfeit.

PMV Testing 1/4 Oz Gold CoinPMV results for a genuine 1/4 ounce Gold American Eagle in a numismatic slab.

Interpretation

It is important to note that while the PMV is an innovative and useful tool in this new era of counterfeit bullion, it, like any tool, must be understood and used properly to be accurate and effective.  Always double check that the correct metal is selected on the PMV menu, and use the sensor selection chart to make sure the appropriate sensor is being used. 

An item that results in an arrow is far outside the range of expected values and is more than likely not the metal it claims to be.  However for an item that falls only a block or two outside the brackets, check for other factors that could be influencing the results.  Does the item have unusually high relief or deep stamping?  Is there a large temperature differential between the item being tested and the PMV itself, such as a coin that just came out of a freezing cold mailbox?  Is the alloy something that is known to be prone to more variation, such as 90% coin silver?

It is always a good idea to follow up a PMV test with visual, weight, and dimensional checks to further evaluate an item.  The sections below go into more detail about known and potential caveats when testing precious metals with the PMV.

Coin Silver

Due to the nature of the "junk silver" alloy and the tendency for there to be impurities in the non-silver 10% balance of the alloy, 90% silver coins will often read slightly outside the brackets on the 90% Coin Silver setting, especially for coins made in the 1950s and earlier.  While the alloy is nominally 90% silver and 10% copper, some coins have a trace amount of lead and/or tin in the non-silver 10% balance, which affects the electrical properties of the alloy and therefore the reading taken by the PMV.  You can test other 90% coins using the Peace Dollar setting, which is a slightly wider range due to the impurities being more common in those coins.  It is also worth noting that all of the genuine 90% coins we have tested, while sometimes reading outside of the brackets on the 90% Coin Silver setting, have tested with the box falling somewhere on the display.  All of the counterfeit 90% coins we have tested have resulted in a left or right arrow, indicating a measurement far outside the expected range.

Silver vs. Copper

Copper and certain copper alloys can mimic the electrical properties of gold and come very close to those of silver.  In these cases the PMV may display a result that falls within the expected range for gold or silver, even though the metal is not gold or silver.  Since copper and copper alloys are less dense than silver or gold, counterfeit pieces made of such an alloy will either be under the expected weight or over the expected size.  For this reason it is always recommended that the weight and dimensions also be checked.

We have encountered a few counterfeit gold pieces using a gold-plated copper alloy that tested as pure gold on the PMV, but they are either under weight or thicker than they should be.  For silver bars and rounds, we recommend first testing on the 99.99% Pure Silver setting, as most commercially pure silver (.999) will fall within the brackets on the 99.99% setting while most copper alloys will not.  If your .999 silver falls slightly outside the brackets on the 99.99% Pure setting, then use the 99.9% setting and also check the dimensions and weight.

If you have a bullion wand, there is an addition Bullion category on the PMV for use with the bullion wand that is more sensitive than the regular sensors.  In our testing using the bullion wand and the Bullion-Silver setting on the PMV, Chinese-made copper rounds and Chinese-made plated copper rounds fell outside of the brackets.  US-made pure copper rounds, however, still fell inside the brackets on the Bullion-Silver setting.  We attribute this to impurities in the Chinese-made copper that are not present in the US-made copper.  This, of course, could change in the future.

A handful of counterfeit gold items still fall within the brackets on the Bullion-Gold setting as well, due to the copper-based alloy used in these counterfeits having the same electrical properties as pure gold.  However, these counterfeits are either under weight or much thicker than the genuine items, as the copper alloy is much less dense than pure gold.

Tilting Wands and Surface Textures

The PMV uses a circulating current to measure the electrical properties of the underlying metal in the piece you are testing.  If there is a gap between the sensor and the metal (such as a numismatic slab or plastic flip), it must be consistent across the entire face of the sensor.  If the gap is not consistent (for instance, if you tilt the wand instead of keeping it flat on the surface of the metal), the reading will not be accurate.  A rough surface texture or deep stamping, often present on poured silver bars, can similarly affect the reading.  The bullion wand is recommended for those instances, as it reads deeper into the metal and can overcome some of those surface obstacles.

Temperature

Temperature affects the conductivity (and therefore resistivity) of metals.  Cold temperatures increase conductivity, hot temperatures decrease conductivity.  An extremely cold sample may read slightly left on the PMV, and an extremely hot sample may read slightly right.  The PMV is calibrated to be used at room temperature and to test samples that are at room temperature.

Numismatic Slabs

The small wand cannot measure through numismatic slabs.  It can read through thin plastic bags, but not much more.  The large wand can measure through slabs, but remember that the coin must be a little larger than the face of the wand when there is a gap between the sensor and the metal.  For the large wand, this means the smallest coin it can measure in a slab is roughly 1/4 ounce.  If the coin is large enough but you do not get a reading through the slab, or get an unexpected reading, try measuring from the other side of the slab.  Often times the coin is closer to front or back of the slab, rather than perfectly centered.  The main sensor on the PMV can read through slabs for 1 ounce and larger coins.

Other Anomalies

A batch of 2015 Buffalo Nickel style one ounce silver rounds produced and sold by Silvertowne LP, both on their website and through eBay, produced inconsistent results with the PMV.  Several buyers reported some rounds reading as expected and others reading 1-3 blocks to the right of the brackets on the 99.9% silver setting, often having a mix of results from rounds received in the same tube.  An independent assay of one of the rounds reading furthest outside the brackets (3 blocks to the right) showed .999+ silver content.  Sigma Metalytics cited micro-cracks on the surface of the rounds as one possible reason for the inconsistent results.  At the time of the issue Silvertowne had been selling a very large volume of the rounds at very low premiums through eBay promotions, and it was thought that the annealing process may have been abbreviated or omitted to speed up production, resulting in harder silver blanks that could crack during the minting process.  Silvertowne was not able to provide a complete explanation as to the reason for the inconsistent PMV readings, but did accept returns from concerned customers and the integrity of the rounds in question was confirmed by the independent third party assay.

The Bottom Line

The PMV is a very useful tool for coin and bullion dealers and serious stackers.  It easily weeds out the most common plated brass fakes and is one of only a few (and certainly the most affordable) options for testing the metal in coins that are sealed in numismatic slabs.  Do not buy a PMV with the mindset that it takes all the skill and knowledge out of testing.  The operator still needs to understand how the PMV works, the physical limitations and caveats of testing the resistivity of a metal, and how to interpret the results.  The fast and non-destructive testing method is particularly useful for those evaluating precious metals to purchase second hand or from the public, and can easily pay for itself by preventing the purchase of just a single counterfeit gold bar.

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