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Steve Herschbach

Target ID / VDI Numbers For Gold Nuggets And Gold Jewelry

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Some good info here.

Those White's detectors,,like it was said,,,some documented small gold rings discovered that rang up with negative Vdi like -6 or so.

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Great thread here Steve..... Kudos..:smile: 

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This is a very informative thread.  Thanks Steve.  Does anyone have a metallurgical explanation why some some steel indicates non-ferrous when it rusts?   I find this most often on some forms of steel wire or cable that has rusted to the core, often disintegrating when you dig it.

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I believe that once the iron oxidizes you no longer have metal..but iron/oxide a mineral...

but you better wait for a smarter person to answer...

fred

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Metal detectors can sense both conductive and magnetic effects. Non-ferrous items have only conductive properties, whereas ferrous items have both conductive and magnetic properties. Many iron and steel items can unfortunately read non-ferrous. This thread goes into the details.

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Setting up your own VLF VDI reference chart.  

Found this thread very interesting Steve, thanks.  

I have a query for yourself and anyone else willing to chime in.

Obviously there are charts showing where certain coins/objects show on the VDI scale - as you have posted.  Due to obvious differences with coins in different countries a different chart would be required for Australia, England, China, etc.  And I'm sure that many of you take your own readings and make your own reference charts.  

My question is:  What is your particular methodology in working out what VDI number correlates to any particular object?  

Do you simply move a dime past the coil, it reads 26 (or whatever depending on the machine) and you record that number?

Or, do you want the dime read at a distance of 6 inches from the coil and record that number?

Or, do you want an 'at coil' reading, a 6" from the coil reading and a 12" from the coil reading.  And in your experience do the VDI numbers change significantly at those 3 different depths?  

Does anyone ever bury these targets in the type of ground they are likely to hunt and then document those VDI numbers rather than the readings of air tests.

The same procedure would obviously need to be done with rings, chains, etc, etc.  

The reason I ask is that I am seriously considering purchasing an Equinox and would need to do this for Australian coins and make my own reference chart.  Simply wondering how others go about this.  

Im not sure if there is going to be a simple or complex answer to this - happy for it to be a thread of its own somewhere more appropriate Steve if you think it warrants it. 

Thanks in advance :wink:

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Charts are usually constructed using simple air tests. The big caveat on all discrimination systems is that ground effects and nearby targets can cause target id numbers to read both lower and higher, so all this really only works on relatively isolated targets in mild ground. It all goes out the window for anything more complex, and in places like Europe with thousands of years of history with different types of finds to be made, you simply dig all non-ferrous targets.

Therefore constructing charts they are only for reference under perfect conditions, and they must be able to be duplicated by others. Air test with moderate sensitivity a few inches from the coil. You want clean, solid repeatable numbers. Trying to go farther will just give you erratic numbers that bounce all over the place.

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Charting is useful when you first start out.  Chart everything.  Treasure and trash.   Chart every type of target identification feature you have available to you.  Chart close, chart far away.   But when you get through charting everything, you'll find that all you really need to chart are a couple of reference items.   

For me,  I only chart nickels and dimes.   Oh..I'll do depth testing with a quarter and a half and a dollar but in reality, if its a high conductor it doesn't really matter what the number is, it gets dug anyway, right?  So the dime is the number I look at, and I want to know stable and fringe depth audio and number response.

For low conductors I really only need the nickel number for a known reference point and then knowledge on how well it holds a nickel id at depth.   Below the nickel is small rings, above the nickel is large rings.

The only other thing I look at is the ferrous / non-ferrous break point.   How soft is this boundary? Is it sharp or is it 6 numbers soft?   

But starting out is always best to bench test the crap out of a detector.  

And then the ground throws it all out the window, of course.   

HH
Mike

 

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2 hours ago, Mike Hillis said:

Charting is useful when you first start out.  Chart everything.  Treasure and trash.   Chart every type of target identification feature you have available to you.  Chart close, chart far away.   But when you get through charting everything, you'll find that all you really need to chart are a couple of reference items.   

For me,  I only chart nickels and dimes.   Oh..I'll do depth testing with a quarter and a half and a dollar but in reality, if its a high conductor it doesn't really matter what the number is, it gets dug anyway, right?  So the dime is the number I look at, and I want to know stable and fringe depth audio and number response.

For low conductors I really only need the nickel number for a known reference point and then knowledge on how well it holds a nickel id at depth.   Below the nickel is small rings, above the nickel is large rings.

The only other thing I look at is the ferrous / non-ferrous break point.   How soft is this boundary? Is it sharp or is it 6 numbers soft?   

But starting out is always best to bench test the crap out of a detector.  

And then the ground throws it all out the window, of course.   

HH
Mike

 

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Thanks Steve, Mike and MineBlab.

Always good to know what the experienced among us do when learning a new machine. 

Thanks again :wink:

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