Have you ever read your owners manual, concerning the effective depth at which you should be able to recover coins, and then after burying several coins, decide to test your metal detector, and to find out exactly what they sound like at various depths, and discover that you cannot detect the coins at all.
There is no way that a manufacturer can compensate for all the different soil conditions that will be encountered by people using their equipment, and still arrive at a suitable overall chart. The are test is the best acceptable method. It is fair to all, regardless of the type of soil that you might have.
Do not worry too much about the fact that you cannot detect the coin for item as deep as the manufacturer said that you might. You definitely have one thing on your side. That is "Mother Nature”. With the help of Mother Nature, you will not only more than likely find coins at the depth that the manufacturer said you would, but very possibly even deeper.
The reason for this is because the item that we are looking for will develop a "Halo” around it, after it has been in the ground for a period of time.
The air test, or the freshly buried coin will not have a "Halo”, therefore it will not be an accurate test of the metal detectors capabilities.
If you would like to see how this works for yourself, try this test.
Bury ten Pennies in your backyard, or some other convenient place. Place the first penny at a depth of in inch, the second penny at a depth of two inches, and the third at a depth of three inches, and continue burying all of the pennies in the same manner, until you have buried all the the pennies. Make sure that all of the pennies are at least 18 inches apart.
In the beginning, you probably will not be able to detect all of the pennies. When you detect the pennies the first time, make a note of what type of signal the pennies produce and how many of them you are able to detect.
Continue testing the pennies for a year or so. and make notes each time that you detect the pennies, regarding the signal you receive.
As time passes, new pennies will be detected at deeper depths. You will be surprised at the depth of detecting that you will gain after only a few months.
This is due to the "Halo”, which os forming around the coins.
Now, another good example of this would be: Have you ever had your metal detector set to reject pull tabs, and then suddenly find a Nickel, without it being with another coin or a piece of junk? We all know that nickels will be discriminated out long before the pull tab.
If this ever happens to you, you will know the reason. You will have just experienced the "Halo Effect.”
The halo is dependent upon several factors, which include mineralization of the ground, the moisture content, the metallic content of the object or coin, and of course, the length of time that the object has been in the ground.
It may take several years for a halo to completely from around an object. The Halo is formed when the soil that surrounds the object, try to take on the same characteristics as the object. This ground saturation makes the coin, or other object appear larger than it actually is.
Once you remove the object from the ground, it will lose some of its conductivity, as the halo remains in the ground.