Would like an explanation?

[Nauti]

Wow that's interesting.I've witnessed this loads of times when a certain machine does great at one site and no good at another...never heard it explained in that much detail though....cheers Mike

 

[TheMarshall]

We've all read on the forums and sometimes elsewhere that air testing a detector is not a good measure of its actual performance as some machines test poorly in the air, but do much better on buried targets. I'd like to see a logical or tested explanation of how that works. Many targets do not leach into the soil as does rusty iron, so the so called "halo effect" can't account for every instance, [size=x-large]especially with silver[/size] or gold that remains inert in the soil. Also, how can a machine recognize a target through soil or another medium, yet do poorly thru the air which would seem to have little or no blocking effect at all? If anyone can pass on a solid, logical explanation to this, I'd appreciate it. Always trying to learn more.
HH
BB

Hello Bill....Just started reading the thread, and yours being the first, I spotted one error ( I like the rest of your propositions ).

SILVER is THE most obvious candidate for of the 'non ferrous' coinage metals that exhibit the 'Halo effect'.

I introduced that phrase into the metal detecting scene, almost 40 years ago, here in the UK.

It evolved from early detecting days of non-motion, non discriminating C'Scope detector usage.

I had a Victorian 'fair' site which oozed silver coins, from the 1800's,....the best from an era of non 'diluted' silver. (95% pure?)

A coin that had been in the ground for a 100 years..undisturbed...in 'sweet' , often damp soil, could be dug up in its own clump of turf.

We always broke the soil clump by hand, and there was your silver coin, surrounded by a halo of silver sulphide. Soil-moisture and electrolysis via ground salts causes such an action.

So when writing about such episodes, I 'coined' the term..."Its silver halo".

The reason the term was introduced, was to explain the fact that such a coin in that state could be detected deeper, due to the halo increasing the electrical 'image' as 'seen' by the then high frequency detector.

The cause for the 'extra' detection depth?......The Skin effect....Where at such a high frequency, the eddy current extends beyond the coin's metal boundary, into the more conductive-than-the-soil band surrounding the silver target......So the target 'looks bigger'.

The unit was the IB100. (100KHz)

Hope you don't mind my 'butting-in', but thought it may help...............TheMarshall.

P.S. Now to read the rest of the thread.

 

[BarberBill]

A lot of interesting and sometimes conflicting ideas came out of this thread. I'm not certain than I completely understand some of the more complex ones and have yet to see a silver coin that 1has corroded or leached off material compared to iron rust etc. so I'm still wondering about a halo effect in that respect, but many seem to go with the theory and of course, if they're digging deep silver that's the bottom line regardless of theories. I've found this hobby and the whole concept of metal detecting to be much more involved and complicated than I ever thought when I started. There's a whole lot more to it than beep and dig a few goodies in the park. Anyway, it's a great hobby no matter what level one aspires to and one of the few that pays back at least a part of the financial outlay.
Cheers and HH,
Bill