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" Halo Effect"
- Thread starter Canewrap
- Start date
Jackpine Savage
Active member
and metal detectors could only get 4-5" on coin sized targets the manufacturers (or maybe the dealers of those machines) invented the "halo" theory to convince people that there detectors actually were deeper than air tests.
Anyone that has hunted the same favorites sites over a few years time in differing conditions of soil moisture and even after the effects of winter cold breaking down mineralization knows that ground conditions alone affect detecting depths on stable non-ferrous targets.
Tom
Anyone that has hunted the same favorites sites over a few years time in differing conditions of soil moisture and even after the effects of winter cold breaking down mineralization knows that ground conditions alone affect detecting depths on stable non-ferrous targets.
Tom
MDers have been buying into the halo effect for a long time. I first had it explained to me 25 years ago.
I think technological knowledge has advanced far enough that we could come up with a better explanation.
As for me, all the hype and confusion are in a different plane. I know that the " FUN EFFECT " is what really counts.
It's fun to discuss and share opinions. I like the experiences discussed here. This is a place where we can raise such issues and not feel as though no one is listening.
Thanks for the input,
I think technological knowledge has advanced far enough that we could come up with a better explanation.
As for me, all the hype and confusion are in a different plane. I know that the " FUN EFFECT " is what really counts.
It's fun to discuss and share opinions. I like the experiences discussed here. This is a place where we can raise such issues and not feel as though no one is listening.
Thanks for the input,
I do think that early on the detector makers used the halo to sell more detectors. I have thought about it for a long while and I can't scientifically prove the halo effect but I have seen cases first hand that makes me believe something is going on that causes items to have better detection than if they were "brand new" in the ground. When I have went clad hunting and have had dimes, pennies and quarters, some on top of the ground but stained have such a large signal that I almost thought it was trash. Even shallow clad sometimes will give a blasting type signal that I could not get simply by placing a coin on top of the ground. So my conclusion is that something is going on but I don't know if it should be termed "halo effect" or not. One instant that halo effect is misinterpreted is when people bury items in their test garden and their detector doesn't fair very well in the tests compared to the real world, that phenomena is the result of disturbing the soil matrix making it more difficult for the detector.
I started testing out the theory over twenty years ago and as the first post says its mainly hogwash with the exception of iron items.
I could never find a machine, even the most sensitive gold detector with smallest coil, that could detect the stain that some coins leave in the soil.
I ended up with large plastic tubes (18" wide) full of different type of soil and different items. Pure gold and silver coins even two-three thousand years old show no corrosion/decay so therefore no halo can have been created. Pure copper coins many hundreds of years old can also be dug that are in the same state as the day they were lost if the soil is neutral. Many Georgian 'coppers' seem to have been made of the sweepings of a foundry floor and other coins either at end of Empire, when things were falling apart or produced in the provinces were adulterated with cheaper metals.
Back to the tubes...if aggressive/acid soil was used and the soil was kept damp then poor quality metals would break down. This created a small electrical charge and allowed slightly deeper detection. This is similar to the principle of the Compass Depth Doubler. Put a charge into the soil and you detect deeper. Drawback, and there always has to be one, is that the iron in the soil is also detected deeper and its masking effect is increased.
Allow the soil to dry out and the depth gain was lost. But the gain is only on poor quality metal that started to eat away. So a slight gain on something thats not going to be worth collecting.
On many soils the coin, whether silver or copper, just produces a nice patina and becomes at one with the soil so no depth gain there.
The really corroded coin retains some degree of slightly extra detectability as its increased its surface area by no longer having a fairly smooth surface and there's more surface being exposed to the acids in the soil.
Funny this topic has come up as one of the U.K.'s 'old timers' has just gone into print in 'Treasure Hunting' magazine saying he can't understand why people like the designers of the T2 and F75 say there's no such thing as halo effect.
I could never find a machine, even the most sensitive gold detector with smallest coil, that could detect the stain that some coins leave in the soil.
I ended up with large plastic tubes (18" wide) full of different type of soil and different items. Pure gold and silver coins even two-three thousand years old show no corrosion/decay so therefore no halo can have been created. Pure copper coins many hundreds of years old can also be dug that are in the same state as the day they were lost if the soil is neutral. Many Georgian 'coppers' seem to have been made of the sweepings of a foundry floor and other coins either at end of Empire, when things were falling apart or produced in the provinces were adulterated with cheaper metals.
Back to the tubes...if aggressive/acid soil was used and the soil was kept damp then poor quality metals would break down. This created a small electrical charge and allowed slightly deeper detection. This is similar to the principle of the Compass Depth Doubler. Put a charge into the soil and you detect deeper. Drawback, and there always has to be one, is that the iron in the soil is also detected deeper and its masking effect is increased.
Allow the soil to dry out and the depth gain was lost. But the gain is only on poor quality metal that started to eat away. So a slight gain on something thats not going to be worth collecting.
On many soils the coin, whether silver or copper, just produces a nice patina and becomes at one with the soil so no depth gain there.
The really corroded coin retains some degree of slightly extra detectability as its increased its surface area by no longer having a fairly smooth surface and there's more surface being exposed to the acids in the soil.
Funny this topic has come up as one of the U.K.'s 'old timers' has just gone into print in 'Treasure Hunting' magazine saying he can't understand why people like the designers of the T2 and F75 say there's no such thing as halo effect.
Brian, you're totally correct, well said.
Halo effect IS real, but ONLY on iron and copper and even then is
dependent on soil acids causing some "leaching" of the metal
oxides into the surrounding matrix. Once that soil is disturbed,
the halo effect is gone. The remaining oxides cannot cause a response
since their effect was only slight anyway. Plus, only certain soils will
produce the effect, depending on acid content. Basically, the oxides
cannot generate eddy currents by themselves but only in well packed
soil around the target metal, where there will be some effect, sometimes.
..W
Halo effect IS real, but ONLY on iron and copper and even then is
dependent on soil acids causing some "leaching" of the metal
oxides into the surrounding matrix. Once that soil is disturbed,
the halo effect is gone. The remaining oxides cannot cause a response
since their effect was only slight anyway. Plus, only certain soils will
produce the effect, depending on acid content. Basically, the oxides
cannot generate eddy currents by themselves but only in well packed
soil around the target metal, where there will be some effect, sometimes.
..W
as Steve (ms) and others have pointed out can make finding deep targets more difficult, or, in some instances, impossible, if one is not careful. I suspect this is where the term GHOST TARGET originated. I learned many year's ago that when one of those ghost target situations occur to remove a little more dirt and the target will be in that removed dirt. I concur that there is no halo effect for gold and silver items, but damp soil does seem to make those targets hit just a little bit harder. HH jim tn
Jackpine Savage
Active member
these oxides have on the old green IH's and Wheats. I find them mostly in damp soil after the winter snows have melted and the ground thawed. It can be a very thick gummy green coating that comes off the coin easily. Whats is the actual property of this "gunk"?... Is it electrically conductive or more resistive in nature? I have never found any of these "spring time" coins deeper than at other times of the year. 6"-8" and thats about it so I have to think there is no gain. As an example, last spring at one particular site I found 3 of these coins within 15' of each other. All 3 were 2 way signals only and seemed to be in the clear with no nearby masking targets, depth about 7" +/-. You would think that if there was some benefit that they would have been clear clean signals from all angles.
Tom
Tom
Jackpine Savage
Active member
You see that all the time on newby posts. The person gets a nice coin signal and digs down 6" and no signal or coin! If its a good quality signal the coin will almost always be just a bit further down or in the loose soil in the bottom of the hole. Checking the dirt pile in all metal is also a good thing to do. Many machines will mask out on the coin if there is a bit of iron in the pile even tho the iron did not prevent the coin from giving a signal in the ground. When I tested the Xterra I found that you had to literally creep the coil over the dirt pile in all metal for it to see a non-ferrous target hiding in there. That was weird!
Tom
Tom
Jackpine Savage
Active member
You're probably right Jim. I do tend to over analyze at times! 
Tom
Tom
Jackpine Savage
Active member
But with the xterra ya still have to go over the dirt very slowly in a lot of cases to let it see the target. Not that it was neccessarilly a bad thing, just something I wasn't use to having to do with other machines in the same field conditions and I mentioned it just a a point of interest..
Tom
Tom
Jackpine Savage
Active member
n/t
Mike Hillis
Well-known member
I can bury a coin and my detector will not report on it, yet it will clearly report on other coins that have been buried longer at much deeper depths. What is going on? We often forget that the ground signal response is many, many times greater than the target signals we are after. In order to report on the coin, the coin response has to be greater than the ground response. What typically happens with freshly buried objects is that the disturbed ground is now isolated from the soil matrix around it and it's response is now so much greater than the coin that the ground is in effect hiding the coin. You could call it 'ground masking'.
Remember that it is the rate of change of the target signal that determines if it will be reported on or not. The fast changing signals from a coin in undisturbed ground can be 'seen' in the midst of the greater, but slower changing ground signal. Disturbed soil itself becomes a faster changing signal within the background of the slower changing ground signal and since it is a very large response, it easily hides the coin response.
Once the disturbed ground is rebonded to the soil matrix around it, it's response has now melded in with the like response of the surrounding ground. Now the the quicker changing response of the coin can be picked up by the detector and responded on. Its an electro-chemical bonding of the soil matrix into a very broad, slow changing ground matrix that lets the deeper targets be detected.
Short version,
HH
Mike
Remember that it is the rate of change of the target signal that determines if it will be reported on or not. The fast changing signals from a coin in undisturbed ground can be 'seen' in the midst of the greater, but slower changing ground signal. Disturbed soil itself becomes a faster changing signal within the background of the slower changing ground signal and since it is a very large response, it easily hides the coin response.
Once the disturbed ground is rebonded to the soil matrix around it, it's response has now melded in with the like response of the surrounding ground. Now the the quicker changing response of the coin can be picked up by the detector and responded on. Its an electro-chemical bonding of the soil matrix into a very broad, slow changing ground matrix that lets the deeper targets be detected.
Short version,
HH
Mike