The most dominant type of metal detector does NOT detect conductivity. They are based on the change in inductance of a coil. ferromagnetic metals increase the inductance of the coil. Non-magnetic, but conductive, metals exclude magnetic fields and lower the inductance of a nearby coil. These will easilly detect a single coin (or bottle cap) but only to a depth of a foot for the best units, and 6" for run-of-the-mill units.
Another, less common for hobbiests, type of detector is the T-R (transmitter, reciever) type. These are a longish boom with a box at each end, usually equipped with a shoulder strap for the operator. The transmitter and receiver use loop antennas aligned so that each is located in a pattern null of the other. Metal distorts the antenna patterns allowing the reciever to pick up more of the transmitted signal. These are insensitive to metal type, but also rather insensitive in general. A soda can might or might not be detectable. However, they do have pretty deep range…6-8 feet maybe. They are very useful for detecting buried electrical cables, water pipes, gas lines, etc…and this is thier primary application. If a soldier were buried with his musket, and it were still intact, you might find a grave with this. If it were only belt buckles and a wedding ring, probably not.
Ah, but they do. How sensitive the detector is to a particular object depends on its size , depth and conductivity. If two objects of the same size and are at the same depth, the higher-conductivity item will return the strongest signal. Remember, the detector works by inducing a small current in the target object, and this current in turn, creates a magnetic field which affects the detector’s search coil. The lower the resistance across the object, the greater the induced current through it will be for a given applied signal strength. The same principle applies to roadbed traffic sensors; aluminum frame bicycles have a better chance of triggering a sensor than a similar steel-framed one.
I’ll limit my hijacking to saying that highly ferromagnetic, yet essentially non-conductive materials (ferrites, powderd iron mixtures, etc.) will yield an extreamly strong signal on any inductive based detector. This signal will be opposite in sign to that produced by non-ferromagnetic, conductive targets, which are detected by the mechanism Q.E.D. alludes to. If Q.E.D. wants to start a thread on metal detectors, I’d be happy to participate (though I may be out of pocket over the upcoming holliday weekend)
Would the age and type of trees help find general areas to search? After 300 years maybe you can’t tell the difference, but an area with “newer” growth in an old growth forest might be a place to look.
I’d love to look at an aerial map of the area, can you narrow the location down for me a bit?
I don’t doubt that dowsers can find water. (I can find buried water and electrical lines by dowsing with 2 metal coat hangers). I don’t think they can find graves.