The mystery of the disappearing coin

[Jackpine Savage]

The part that brothers me most is not getting a signal in my plug, especially after flipping it over. That puts the coin so much closer to the surface and my 705 isn't picking it up?[/quote

It has been a few years since I had an X-terra (an early 70) but I quickly found out that you have to move the coil very slow over a flipped up plug at times in order to for the detector to pick up the target.

 

[argyle1]

Spot on re copper halo's.
How many times an old English copper coin would scream in at 14 inches in moist ground or heavy mineralized gullies that you'd swear were surface hits I couldn't count.

Hey in regards to the missing signals on turned over plugs, have you guys always got DD's on when this happens to you?

I dont live in the USA, but I've sort of picked up that wheat cents are fairly old coins. Being older,it probably means that when you find one, it has been in the ground a long time. From what I've gleaned, they are made of copper, and are not clad. I've found, over time, that copper coins, when left undisturbed in the ground for a long time develop what some of us call a "halo effect". This is caused by metal from the coin leaching into the ground around it, and it will develop so long as the ground is not disturbed. The effect of this is that your detector signal senses a larger object than is actually there, and can give a good signal on a deep coin. When we dig a plug, we disturb the soil (in the ground as well as in the plug) and so a coin does not "look" the same to the detector as it did before the ground was disturbed. If the coin is deep, your detector may not pick it up if it is at the bottom (or deep in the side) of the hole. The same thing can happen if the coin is still in the plug, and the plug is a big one. The coin has lost its halo, and the detector cant "see" what it did before. This is where a pinpointer can help, because you can put it into the hole, whereas you may not be able to put the coil in the hole. Sometimes you may have to destroy your very carefully removed plug, and a pinpointer can help there too. HH BTW, this phenomenon occurs with many vlf detectors.

 

[BillF]

Hey in regards to the missing signals on turned over plugs, have you guys always got DD's on when this happens to you?

So far its been when I had the 10.5 DD on. I'll have to pay more attention if it does it on the others.