Here is a lengthy post from "Chris' Metal detecting page" Best I could do for now.... I don't know Chris' credentials... TTC
I. The Trouble With Test Gardens
The fresh-burial test for coins has led many a detector owner to conclude his new machine is "no good". That's because this test is nothing more than a worsened version of the Air Test.
You bury a coin six inches deep... and ten minutes later, you see if your machine can detect it. Perhaps you get no signal whatsoever. Maybe you even start to become discouraged, thinking you bought a lemon.
This is like doing an air test, where the air is made of soil. It fails to take into account an extremely important factor, which we'll discuss shortly.
II. The Controversy
Some topics engender controversy way out of proportion to their importance in the world. This is one such topic. There are actually people on detecting forums who have stopped talking to each other entirely, all thanks to this itty bitty subject that revolves around whether or not a buried coin produces an ion halo. It's not because the debates were especially animated, either.
I'm just going to try to present scientific principle and fact here. Take it or leave it. Really, this article is not meant to stoke the fires of debate; it's for the newbie who just bought a detector and thinks it's no good because it can't seem to find a quarter that was just buried in the front yard.
Some people believe the "halo effect" theory has been disproven. However, I have yet to see a peer-reviewed scientific journal article that even comes close to doing this. In fact, everything I have seen points the other way. I'm talking about scientific principles here, not opinion.
Many people understand that iron objects form a halo, but they go so far as to claim that copper and silver objects cannot form halos.
This claim is not at all true. The timetable required isn't even all that long; certainly it's less than a hundred years, unless you live in the Atacama Desert.
It is understandable, of course, since silver and copper have traditionally been thought of as "noble" metals. They're just not as noble as platinum, palladium, or gold. In chemistry, the term "noble" is roughly synonymous with "non-reactive" or at least "not very reactive". The term is used in conjunction with metals, and gases. Xenon is a noble gas, for example, while palladium is a noble metal (though not one of the three traditional ones of antiquity).
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[TD]Does silver ionize in the ground?
Nahhh.... ;-)
This 1918 Merc was found in the woods, a few inches deep. Pine needles and oak leaves covered the forest floor. Organic acids, anyone? It's pretty clear there was sulfur at work here, too.
Silver will give an "ion halo" wherever groundwater or moisture can work on it for decades, especially if that water is even slightly acidic (which it nearly always is).
When the black coating was removed electrolytically, it revealed only minor pitting of the surface. Surprise!
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Have you ever dug up an old copper coin and found that it was green with corrosion?
What do you think that means?
How about a 90-year-old silver coin that emerged from the soil all blackened with tarnish? Instead, perhaps, it emerged with just little traces of black, brown, or even other colors. That's OK, too.
There doesn't have to be noticeable blackening to mean that ions have formed. Silver sulfide is not the only possible compound that can form. Some of the compounds are at least partly water-soluble and can leach out a couple inches into the surrounding soil. Furthermore, it doesn't take much ionization to make the surrounding area conductive.
Recall also that some water-insoluble compounds can become appreciably soluble when that water is slightly acidic (
e.g., because of some H[SUB]2[/SUB]S, H[SUB]2[/SUB]SO[SUB]3[/SUB], HNO[SUB]2[/SUB], tannic acid, etc.)
In the ground, ions are mobilized from the surface of a coin by soil acids and dissolved salts. Rain picks up atmospheric NO[SUB]2 [/SUB]and especially SO[SUB]2[/SUB], as well as tannic acid (etc) leached from pine needles, oak leaves, and other materials on the surface. There is also decaying pyrite in many soils; this yields H[SUB]2[/SUB]SO[SUB]3[/SUB], H[SUB]2[/SUB]S, etc. Pyrite is one of the commonest minerals there is; it can be present in all rock environments, from igneous to sedimentary.
Anyway, so you buried a coin 6 inches deep yesterday. Maybe you can't detect it. If you come back in a year, or perhaps five years, this could change. It will not change in just a few days (or weeks), unless the object is made out of something reactive like magnesium or zinc.
With a very slow-reacting metal such as silver, you really ought to come back in thirty or forty years to notice a difference. Or, if you want to do a useful experiment, you could come back every week and see how long it takes for your favorite detector(s) to get a faint signal over the coin. Perhaps someone could speed the process by burying silver coins with egg yolks, and copper coins with vinegar. I've been wondering how 5% HNO[SUB]3[/SUB] would work here, instead.
Since salt water is notorious for promoting corrosion (
i.e., promoting ionization of metal), it might work instead of acids. You might be able to get a good test garden without waiting years.
, long story short, is it humanly possible for this machine to find the goods like barbers or seated at a deeper depth like 8". oh yeah i should mention i did do a test plug in my yard with a standing liberty we had, it found it no problem at 4 and 6 but was a bit sketchy at 8, i had to pinpoint the hell out of it to locate it. any help is appreciated...
