7/8/16 Report - Halo Effect, Ground Effects, and Notes On Testing Your Metal Detector. Kirlian Photography.

Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.

Kirlian Photograph of US Half Dollar.
Source: See link belwo.

Yesterday I discussed air tests and ground tests and pointed out one common problem with both of those kinds of tests.  That problem was the say the coil or target was moved.  Today I'll discuss a completely different problem.

If you understand these problems, you'll also have a better understanding of how your detector works, and as a result, be able to use your detector more effectively in the field.

People often bury for ground tests. Some create test gardens.   I'll maintain that very similar results can be obtained by simply laying the target on the ground and then raising the coil above the target.  Little is gained by burying the target.  When the ground is neutral, it can end up being nothing more than a glorified air test.  When the ground isn't neutral, it can end up being worse than an air test for reasons I'll discuss below.

One reason, but not the primary reason, is that the soil is unsettled and loose, but also the object can be standing on end or in some other odd position unless care is taken to position it.  As I've shown in the surface angle of the target is an important factor.  A coin standing on end, for example, will typically give a small and uncharacteristic signal.

When a target is buried for a metal detector test, it is not like the typical target you most likely find during a hunt because during an actual hunt the target has typically been in the ground a while.  As a result there is what is called the "halo effect."

The "halo effect" theory holds that buried metal objects have an ionization "halo" that increases their apparent size to a metal detector searchcoil.  This makes the objects detectable at greater depth.  In other words, according to this theory, long-buried metal objects have something you cannot duplicate with a recently-created test garden.

It takes a while for the halo to form, and the halo effect is greater with objects that have been buried for a longer time.  The halo effect is also increased in certain environments, such as saturated soil.

Here is a web site that discusses the halo effect in detail.

http://www.njminerals.org/metaldetecting-haloeffect.html

Remember also what I've said about compacting sand and soil.

The lack of a halo effect is not the only problem with newly buried targets.  When there is any degree of soil mineralization or conductivity, digging a hole creates discontinuous ground conditions that a metal detector will try to adjust to.  Such disrupted sand or soil will cause your computer to adjust and will often cause false signals, and often a reduction in depth.

It is not unusuaal to detect a coin in black sand, then dig a hole only to find that you can no longer find the target.  In some cases that is due to the difficulty your detecdtor is having in adjusting or interpreting the ground conditions created by the disrupted matrix created when you dug the hole.

OF course different detectors will adjust differently and different settings will also affect how your detector adjusts to those circumstances.

Perhaps the easiest demonstration of this is in black sand at the beach.  The next time you encounter black sand give it a try.  Dig a hole in a concentration of black sand.  You very well might find that you get a signal from that hole.  If you toss a coin into the hole, you might have difficulty detecting it, especially at depth.

It is very much like when a wave comes washes over dry or partially dried sand at the beach.  There will be a line between the newly wet salt sand and the dryer sand.  Sweeping across that line can cause a false signal or a reduction in detecting depth as your detector tries do adjust to the difference.

Regarding the halo effect, here is a summary of three main points from the previously referenced web site.

1.  Test gardens aren't much good unless they are old because the Halo Effect hasn't formed on newly buried objects.  New test gardens are not much better, if any, than an air test.

2.  Noble metals ionize in the ground too.

3.  Some environments create the Halo quicker than others, such as moist and acid environments.

My main point is that not only will the halo effect not be present when a target is newly buried, but there are also other problems, including the fact that the soil matrix has been disrupted.  In some circumstances, that can be a very significant problem.  That will make ground test results different from what you would get from a naturally buried and settled object in the field.

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That reminds me of some Kirlian photography that I used to do.  Kirlian photography allows you to capture an image of elecrical fields around an object, very much like the halo effect.

Here is a little about that.

In 1939 Semyon Kirlian discovered that you could photograph the aura of an object by placing the object on a photographic plate in a high-voltage electric field. The photographic image looks like a colored halo or coronal discharge.

Images created by Kirlian photography were mistakenly thought by some to be a physical manifestation of the spiritual aura or "life force."  What is actually recorded is the result of natural phenomena including pressure, electrical grounding, humidity and temperature. Changes in moisture barometric pressure, and voltage will produce different 'auras'.  So what is actually seen on the photographic plate is gas ionization around the object - living or not.  

Here is a link where you can read more about Kirlian photography and auras.

http://www.skepdic.com/kirlian.html

And here is a link where you can find the photo of the coin shown above plus a variety of other Kirlian photography. 

http://www.bing.com/images/search?q=kirlian+photograph+of+a+coin&id=488C10464835EA7AE5DD735739335BE5CC19D7E3&FORM=IQFRBA#a

And here is the Kirlian photography system that I once assembled in an old brief case.  I did a post about that some time ago.

Kirlian Photography System Assembled in Brief Case

Inside the case (top photo) you see a variable voltage trasnformer and a high frequency induction coil.

On top of the case is a metal electrode plate and a glass dielectric plate.  The glass plate is placed over the electrode plate, then Polaroid film places on top of the glass plate and the object to be photographed placed on top of the Polaroid film.  Then, while in a completely dark room, push the button (white seen through the hole in the case) and the aura is created and picked up by the film.

Unfortunately I can't find any of the old photos I took with this equipment.  I should be able to make some new ones once I warm up this old system.

I intend to get that old system up and running again and take some more photos of coins and other targets.  

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I wanted to express my deep felt sympathies for those who were killed yesterday as well as their families.  It is too bad what has become of our country.

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On he Treasure Coast expect more hot weather and calm surf for days to come.  There is not tropical activity to watch either.   Low tide will be around 5:30 today.   There will be some slightly negative tides.

Happy hunting,
TreasureGuide@comcast.net

7/6/16 Report - How To Conduct More Meaningful Ground And Air Tests With Your Metal Detector. Summer FUN Convention.

Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.

Florida United Numismatists, Inc., is hosting the 10th Annual Summer FUN Convention in Orlando Florida, July 7 - 9 2016. The convention will be held at the Orange County Convention Center, 9800 International Drive.

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I was looking for something the other day - don't remember what - and ran into a video showing some fellows testing and comparing metal detectors on a small piece of buried gold.  They did what most people do.  They buried their target and tried the different detectors to see which did the best. Only one detector gave a good strong signal on the target.  Although I saw a few problems with their method of testing, I wanted to focus on one problem that is not usually seen as a problem.  Almost everybody makes the same mistake.

As you know, there are several things that will affect a detector's signal.  The nature of the target is one thing.  Its composition, size, shape and how it is laying will all affect the detector's signal.

Of course the ground will affect the detector's signal.

And the environment, including such things as electrical interference, will affect the signal.

So will the detector's settings.

But one thing that is not often taken into account is the behavior of the detectorists.  If you watch either an air test or a ground test, you'll always see the same behavior.  The target, relative to the coil, is moved rapidly, in very short sweeps, and right over the sweet spot of the coil.  That is not how the coil is moved in actual field use.  As bad as that is, there is yet another problem.  The exact position of the target is known, which is not the case when you are hunting.  That is a more serious problem than you might think.

When scanning ground during a hunt, the coil would usually be move more slowly, and the target would usually not be directly under the sweet spot of the coil.

When conducting either an air test or ground test, if you want to get results that are similar to actual field performance, the exact position of the target should not be visible to the operator.  I've conducted psychology experiments and know something about how the sensory systems work.

There is always some level of noise, and a signal can be interpreted as noise, and noise can be interpreted as a good signal.  When the location of the target is known, any noise that occurs when the coil is over the target will be interpreted as noise, and the threshold for detecting a good signal in noise will be much lower when the operator knows when there should be a signal.

I've done this myself when I was testing a new detector in a noisy environment with a lot of static. Noise when the coil is over the target will often be interpreted as a good signal when it is actually noise.

People do not realize how much the tendency is to interpret noise or a marginal signal as a good signal when you know that the coil is centered over the target and a signal is expected..  You know when there should be a signal and therefore interpret almost anything as a good signal when you are expecting a signal.  Noise created by hitting the ground or grass or any random noise will be interpreted as a good signal when you know that the coil is over the target. That tendency is multiplied by a coil that is being moved in short bursts over the spot.

The stereotypical very short and rapid movement that is inevitably seen during air tests and ground tests when the location of the target is known and centered under the coil, is unlike anything that would normally happen in the field, except after a target has been located and is being pinpointed.

To get more significant and realistic air and ground test results, move the coil relative to the target like it would be moved during a hunt.  Remember, most of the time in the field the target will not be under the sweet spot of the coil.

In addition to moving the coil more realistically, during ground tests the operator should not be able to visually identify the location of the target.  He can close his eyes and start a few steps away, proceeding the same way he would in the field.  You might be surprised by how often the target is missed altogether when that is done.

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Gold and silver prices have been going up for the last few days.

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It looks like we'll be having another week or two of smooth surf on the Treasure Coast.  There is no tropical weather to watch.

Happy hunting,
TreasureGuide@comcast.net