Question about buried targets, halos, fresh, old, etc.

[glabelle]

I'm looking for a technical explanation of the difference between freshly buried and long buried targets. In particular, it seems to be "common knowledge" that coins buried a long time, give a different response than freshly buried coins. This is of interest as it relates to building a test garden and confirming the results one gets with it.

It seems to me that copper/nickel coins can indeed be dissolved or "rusted" by chemicals in a soil over time. This may indeed result in the target "looking" larger (halo effect), especially when the soil is wet. I'd like to know what other effects it would have on detection. i.e. amplitude/phase causes a different ID, or the signal returned is weaker or greater.

Question number 2 is the one that bothers me the most. How can a silver, or gold coin for that matter, be effected in the same way - or is it? Silver is a pretty inert metal. I cannot think of any chemicals, found at typical hunting sites, would have the capability of reacting with silver. The empirical evidence of this is that even really old silver brought to the surface, usually shows no signs of deterioration and can look like the day it was dropped. I fail to see how there could be any difference in detection response between a long buried and recently buried silver coin. Can anyone confirm this one way or the other through actual experimentation or measurement?

Thanks,
George in Aloha, Oregon

[Skippy]

A bit of searching the forum, and use of Google would have found these articles easily:http://www.geotech1.com/forums/showt...he-Halo-Effect andhttp://www.njminerals.org/metaldetec...aloeffect.html You will see that silver isn't pure, it is 90% or 92.5% commonly, so the copper can leach/corrode, and silver is not inert either. Being in the US, your idea of old silver is different to those of us in Europe. I can assure you that 800 year buried sterling silver coins can have heavy corrosion deposits on them - black, yellow, depends on the ground they were in, but occasionally even coins this age come out 'shiny'. Regarding target ID's, my experience is the corroded target will read 'lower', ie. towards the foil end of the range, which could be due to the pitted surface being higher-resistance, so currents circulate differently to the smooth original surface. It could also be due to one metal from an alloy leaching out, leaving voids in the remainder.

[glabelle]

Skippy, I read the articles and saw no technical summary of proof that older buried silver read differently than newly buried.
I'm on the West Coast of the USA. I've hunted for 50 years. I've found my share of silver dimes and quarters - buried no more than 100 years. We have moderate mineralization here. I can tell you that all the deep silver I have found was weak and pinpointed very narrow. No noticeable "enlargement". About 1 out of 50 coins are black from contamination, but the detectors I've used (many models) never showed a difference in ID between a black coin and a shiny one.

George

[Skippy]

As most of your silver coin targets are presumably 50 -150 years old, they are probably not corroded enough to have a significant ID change. I can't say whether 800 year old silver has an ID change, because there are no uncirculated/non-buried examples to compare against. The concept of the halo effect as I understood it was that the coins etc gave a stronger response, ie. appeared shallower than their true depth. They wouldn't necessarily appear larger by any obvious amount. There has been some discussion of test gardens on Tom Dankowski's forum (dankowskidetectors) as in one of his DVD's he covers the construction of a variety of recreated scenarios - iron masked, coins on edge, low conductors, high conductor etc. It may be worth having a look there.

[Carl-NC]

George, there is no consensus on halo effect outside of maybe iron. Gold certainly doesn't corrode or leach, silver barely, and copper some. Whether any of this helps with eddy current response is doubtful and unproven in any case. All we really have are testimonials. Freshly buried targets result in disturbed soil which, in some places, can affect detection depth.