Understanding the Halo Effect

[danhughes]

When a coin has been in the ground for a long time, it is attacked by outside elements. The result is that ions of metal from the coin are leached out into the surrounding ground.

This is called the Halo Effect, and it causes the coin to look larger to your metal detector. That's why you can find older coins easier than you can find newer coins at the same depth.

My newest podcast (internet radio show you can listen to on your computer) gives you the facts about the Halo Effect, and tells you how you can take advantage of it.

Go to http://thetreasurecorner.com and click the pink button to listen to this short (about 4 minutes) program.

---Dan Hughes, http://treasuremanual.com

[J_Player]

When a coin has been in the ground for a long time, it is attacked by outside elements. The result is that ions of metal from the coin are leached out into the surrounding ground.

This is called the Halo Effect, and it causes the coin to look larger to your metal detector. That's why you can find older coins easier than you can find newer coins at the same depth.

My newest podcast (internet radio show you can listen to on your computer) gives you the facts about the Halo Effect, and tells you how you can take advantage of it.

Go to http://thetreasurecorner.com and click the pink button to listen to this short (about 4 minutes) program.

---Dan Hughes, http://treasuremanual.com Hi Dan,
What is your source of the facts you broadcasted telling how halo works?

Best wishes,
J_P

[danhughes]

Hi, JP. I've heard from a lot of people after I posted that show, many of them taking issue with the whole concept of the halo effect.

Perhaps the term "halo effect" is a poor name, but I've experienced the phenomenon many times.

I used a multitude of sources, but here's the best article I found on the subject:

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

Best,

---Dan

[Qiaozhi]

Hi, JP. I've heard from a lot of people after I posted that show, many of them taking issue with the whole concept of the halo effect.

Perhaps the term "halo effect" is a poor name, but I've experienced the phenomenon many times.

I used a multitude of sources, but here's the best article I found on the subject:

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

Best,

---Dan
There is one important error in the halo effect reference - copper is not a noble metal.

There is also a photo of a silver coin with a black coating. This is clearly the result of tarnishing. That is, the result of a hydrogen sulphide reaction with the silver surface. This is the same reason you have to polish your silverware to restore the shine.

Personally I have only experienced the halo effect on a few occasions, when recovering deeply buried copper coins, but never with silver coins. In cases of extreme depth for single coins, the real reason is usually that the coin was lodged in the side wall of the hole, and falls out during the excavation.

[J_Player]

Hi, JP. I've heard from a lot of people after I posted that show, many of them taking issue with the whole concept of the halo effect.

Perhaps the term "halo effect" is a poor name, but I've experienced the phenomenon many times.

I used a multitude of sources, but here's the best article I found on the subject:

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

Best,

---DanHi Dan,

I am also familiar with the "halo effect". I experienced it several times while metal detecting over the years. I think "halo effect" is a good name for it because nobody knows exactly what causes it, while it has properties that resemble a halo around the target.

When I read your post saying "When a coin has been in the ground for a long time, it is attacked by outside elements. The result is that ions of metal from the coin are leached out into the surrounding ground. This is called the Halo Effect, and it causes the coin to look larger to your metal detector." ... you added causation to the definition. The halo effect is the phemomenon of a metal detector showing a large signal that becomes smaller after the target metal is dug from the ground. "Halo effect" has never been shown to be connected with leaching metal ions in the soil. This is only a theoretical assumption advanced by Chris on his web page and others who speculate on why we observe the effect.

You are correct this is a controversial topic.
There are people in this forum who say the "halo effect" has been proven not to exist other than a slight increase in signal for rusted iron. And others have long explanations to detail exactly how it works. But nobody has ever shown any convincing evidence that demonstrates ions from corroded metal are causing a larger than normal metal detector signal. In fact, nobody has set up any field tests to measure exactly what is causing the larger than normal detector signal to my knowledge. This is not surprising because you would first need to locate a buried metal object that has produced a "halo", then take electronic and magnetic measurements before digging the target. How would you do that?
If you did have a known long-time buried target metal, then how would you make your measurements of the soil electronic activity and magnetic activity without disturbing the soil?

The source of information you posted is made by someone who started with some basic chemical reactions that can happen to various metals, then interjected his assumptions that these chemicals exist in sufficient amounts in the soil to produce enough ions to form a "ground battery" that will form a conductive area around the buried metal. He further assumed this conductive area will develop eddy currents when a metal detector coil is passed over it. He goes on to say that a dc electric field from these ions at the buried metal helps the halo effect to work. Then he backed up his explanation by saying nobody has ever disproved it, and he's talking about scientific principles here, not opinion. I guess that is supposed to prove he is right. Yet he has not offered a single example that can demonstrate the ions from corroding metal produce the alleged increase in eddy current that we call halo.

He is correct, his theories haven't been disproven. And they have not been proven either. They are just untested theories he is advancing. The only thing that was ever proven is there is a "halo effect" observed by hundreds of detectorists. But can it really be working the way he says? I doubt it.

What we do know is that in some cases, a long-time buried metal object will give a larger than normal signal until after it is dug. Your source of information would have us believe the larger signal is caused by corroding metal ions creating a battery in the ground, with the help of water and natural acids and sulfur compounds that are rinsed into the soil when it is rainy. This is what he is assuming based on elementary chemistry and electricity principles. He has shown no field evidence to suggest that this is what is causing the larger signal. He just assumes this is what happens because it seems logical in theory. In fact there is a large body of scientific evidence that suggests this is not the mechanism that is taking place.

Some of his assumptions are wrong.
For example his idea that gold does not corrode in the ground is wrong. The corrosion of gold and release of gold ions in the soil has been studied by scientists with peer review for over 20 years. This is well documented, and is used to advantage in exploration of gold mines to pinpoint the gold bearing deposits that may be located thousands of feet below the surface and often much closer. When looking to pinpoint gold deposits, scientists measure gold ions in the soil, not the base metals gold is alloyed with.
Why would Chris assume gold or platinum does not corrode? Because people told him it is a noble metal? ...So he assumed without testing or checking it out.
He also talks about how water is a key ingredient in order for these ions to form. Of course, he knows moisture is necessary to form a solution suitable for an electrolyte in a battery, so he assumes it is a necessary ingredient for metals to corrode and form ions. But this simply isn't true. Gold, copper, silver, zinc, lead and most other metals have been shown corrode and form ions in the soil with or without moisture. There are even gold mines where gold has been corroding miles deep in rock veins without water present.

And what about his proclamation that the "extra area of conductivity" is responsible for the "halo effect"? Is this also an assumption? Did he actually measure the extra eddy currents in the soil around the buried metal? I think he assumed this too. I have never seen anyone disprove that there could be significant extra eddy currents in the soil. But I never saw any evidence shown to demonstrate there are extra eddy currents in the soil around a corroded coin. It does not even make any sense to say the extra ions are reacting to a search coil by making eddy currents. We know a good conductor is needed in order to form measureable eddy currents, and ions in the soil are not good conductors like a chunk of metal is.

Then what about the DC electric field created by this "buried metal battery"? Has anyone ever measured this electric field to see just how strong it is above a long-time buried metal object? Or does he assume it is strong enough to be responsible for the "halo effect"? What does a static electric field of maybe one volt have to do with a metal detector search coil anyway?

I know there is such a thing as the halo effect from my own experience, and from hundreds of reports from others who also observed it. But I find it hard to believe it is caused by the mechanism of base metals leaching out into the soil and producing an electric field and larger conductive area for eddy currents to register on a search coil. Can I prove it? probably not. But you can.

Here are some simple experiments you can do to see for yourself if metal ions in the ground will produce a halo:

Experiment 1:
Get a penny and put it in a cup with one ounce of warm water. Add a few drops of sulfuric acid (battery acid) and watch for a chemical reaction. The color of the water will change when the penny is dissolving, remove the penny from the liquid and bury it 6 inches deep. Then dump the remaining acid solution on top of it, and fill the hole. Also bury a second penny about 10 feet away without any acid. Wait a few days for the acid to continue corroding the coin. Then return to the location and see if you find a halo effect from the penny with the acid. Compare the signal from both pennies to see if there is any difference. Try measuring the electric field at the location where the corroding penny is.

Experiment 2:
Get two recent US pennys and sand one face of each of them until you arrive at the zinc core exposed on one side of each coin. When you see one half of the coin is zinc, and the other half is copper, then paint one of the coins with clear fingernail polish so it is insulated on the outside, and leave the other penny uncoated. Bury them in two separate holes 6 inches deep about 10 feet apart from each other. In the hole where the bare penny is buried, dump about an ounce of salt water on it. Also squeeze the juice of a lemon on it, then fill the hole with soil and let it rest awhile to reach equilibrium. You should now have a buried zinc-copper battery that is discharging through the citric acid and salt electrolyte. In the other hole, the penny is the same weight, but it is insulated, with no ionic or electric action reaching the soil. You have now created a "ground battery" much stronger than can be expected from a penny buried in ordinary soil for 10 years or so. See if you notice any halo effect at either coin when passing a metal detector over each of the two holes.

Experiment 3:
Get a 9v battery and put it in a plastic sandwich bag so it cannot get wet or contact the soil at the terminals. Bury it 6 inches standing upright, and take some metal detector readings to see what kind of signal you get. Then dig the soil until you uncover the top of the battery, and cut the plastic bag to expose the terminals. Pour some water in the soil you removed until it becomes very damp. then pack the damp soil around the 9v battery terminals for good contact so there are ions formed from the metal of the battery terminals. Fill the hole with the remaining damp soil. You have now created a much stronger electric field and current flow than a typical long-time buried coin can generate. Most buried coins cannot develop as much as two volts in the very best of conditions, while you have 9 volts. Now you can check to see if there is any difference in the signal from your detector with this extra strong battery causing ionization at the terminals and a much stronger current flow.

Experiment 4:
Cut a piece of copper wire or pipe that weighs the same as a penny and dissolve it in an ounce or two of muriatic acid. After it is completely dissolved, dig a small hole and place the soil back in the hole loosly. Then pour the liquid with the dissolved copper into the loose soil, and press it down so it is compacted like the surrounding soil. You now have a penny weight of copper ions dissolved in the ground... much more than corrodes from the side of a penny over many decades. Take your metal detector and see if you can find the halo the next day.

These experiments don't prove anything, but they may give you some strong evidence to demonstrate that the electric field and dissolved ions are not what is causing the halo effect.

Nobody so far has shown what exactly causes the some long-time buried metals to show a "halo effect". But there is plenty of evidence to show some of the assumptions that Chris passes of as "facts" can easily be proven to be wrong. For one, gold and other noble metals do corrode, and thier ions are being measured to locate metal buried in the ground. Secondly, the simple tannins and sulfur compounds at the surface are not the main mechanism responsible for dissolving metals in the ground. Scientist have shown that the bulk of buried metals are dissolved by other means, while the surface chemicals play a larger role in re-combining the metal ions as compounds which can be later eroded away as salts. The actual research done does not give any explanation for "halo effect", but it shows the folly of jumping to simple conclusions when figuring out how things work based on speculative assumptions that were never checked out to see if they are correct or not. As long as we are making podcasts, it might be good to limit the facts we broadcast to known facts rather than passing off erroneous assumptions as facts.

Maybe it would be good to read some real science articles about metals corroding and forming ions in the ground.
Here are some links that will show you some actual facts that were measured in the field by scientists, not simple theories based on high school chemistry and electronics:

Scientists have made thousands of measurements that show microbes are largely responsible for the corrosion of buried metal causing it to release ions into the soil (see http://www.nature.com/ismej/journal/v1/n7/full/ismej200775a.html ). According to geomicrobiologist Frank Reith, "...the precipitation of gold by micro-organisms, and thus in the biomineralisation of gold, which as recent evidence suggests has led to the formation of some of the world largest gold deposits."
But in addition to micro-organisms precipitating metallic gold, there are microbes that ionize and dissolve gold:
"In soils with high contents of organic matter heterotrophic bacteria and fungi appear to dominate the gold dissolution by excreting amino acids, low molecular weight organic acids (LMWOAs), cyanide or organic sulfur compounds. These molecules were shown to have the ability to dissolve native gold and act as complexing agents for the resulting gold ions."

All manner of microbes including bacteria, yeast, actinomycetes, fungi and algae and other micobes have been found dissolving buried metals in the presence of water or without water. These microbes actually get their nutrition from digesting metals, and secrete cyanide that can dissolve gold or platinum. Further, they produce organic acids and sulfur complexes that can suspend metal ions until they become bound with other elements near the surface (see http://books.google.com/books?id=L8Be8rprGgkC&pg=PA495&lpg=PA495&dq=microb#v=onepage&q=&f=false ). These microbes work on nano scale, but over a period of time, they dissolve and precipitate significant amounts of gold and other metals causing them to move to a new location in the soil. Large gold deposits have been found in Australia that were formed by microbes depositing dissolved gold ions as a precipitate on the surface of existing smaller nuggets. They found the outer layer of gold was much purer than the gold alloy in the center of the nuggets ( http://crcleme.org.au/NewsEvents/News/Archive/2004/AUSIMMReith.pdf ). Scientists estimate that over 1% of the world's gold is dissolved and precipitated by microbes ( http://www.springerlink.com/content/u142554485g84k31/ ).

Here is an article showing how treasure was found in decaying tree stumps: http://www.sciencedaily.com/releases/2007/08/070818101731.htm

Does gold corrode? Scientists show what they found from microbes precipitating gold:
http://www.sciencedaily.com/releases/2009/10/091007103034.htm
http://www.geotimes.org/sept06/NN_Microbes.html

"Geologists are studying bacteria nowadays. It's not that the rock hounds have gone soft. Instead, they've found that geological processes once attributed solely to simple inorganic chemistry, inorganic chemistry have microbialmicrobial fingerprints all over them":
http://www.thefreelibrary.com/Attack+of+the+rock-eating+microbes!+Some+bacteria+break+down+...-a0110963009

Microbes precipitating gold in a mine 2 miles deep:
http://www.ornl.gov/info/ornlreview/rev32_3/amazing.htm

Microbes growing gold nuggets:
http://www.abc.net.au/science/news/stories/s1032376.htm

Gold-eating microbes:
http://aem.asm.org/cgi/reprint/67/7/3275.pdf

Microbes convert dissolved gold ions in the soil into gold particles:
http://www.gold.org/news/2006/07/14/story/4417/microbe_makes_gold_out_of_dust/

Breif explanation of vertical metal ion movement and soil anomalies:
http://geea.geoscienceworld.org/cgi/content/abstract/5/3/201

Gold, silver and palladium ions are measured to pinpoint deposits:
http://www.thefreelibrary.com/Gold+Canyon+Receives+Fedikow+Report+on+Springpole' s+MMI+Program-a0128214628

Report on bacteria bio-processing gold:
http://www.sciencedaily.com/releases/2006/08/060802103513.htm

Bioleaching methods for metals from the ground for industrial recovery:
http://www.kanglaonline.com/index.php?template=kshow&kid=1424

Over 380,000 reports of mining exploration companies measuring dissolved gold ions in the soil to pinpoint buried gold deposits:
http://www.google.com/search?q=mmi+gold&hl=en&start=10&sa=N

Over 200,000 articles about microbes and gold from Google:
http://www.google.com/search?hl=en&q=gold+microbe&btnG=Google+Search&aq=


The point to looking at this research is that we are not consigned into believing whatever pseudoscienc someone dreams up from their own conclusions. There is no need to teach others scientific principles taken out of context or even broadcast wrong facts when we have a body of real science data that tells a large part of the mystery of how metals corrode in the ground. Maybe some day someone will actually make some field measurements that can explain how halo really does work.

Best wishes,
J_P

[danhughes]

JP, I hope that what you wrote here was mostly cut and paste from something you penned earlier, because that is the longest response I've ever received to one of my shows - at least the longest response with scholarly citations. It must have taken you hours to research sources if you did this from scratch. Jeez, I spent less time writing term papers.

I want to assure you I'm not one to normally spread urban legends. I was just blindsided by the halo effect problems; somehow I found a ton of pros, and missed all the cons. Had I talked with you before I did the show, the program would have been quite different. (By the way, to show you the other side of the coin, I got a lot of heated response from dowsers when I did an expose show about those "long-distance locators". I'm a Snopes guy all the way.)

I do appreciate the information you provided, and I'd like to do a followup program using your material.

But I need your help.

Can you possibly reduce the pertinencies in your post to about 3 minutes of easier-for-the-masses-to-understand highlights? We have to dumb it down a bit for the masses. (I have an MS in Technology and I don't fully understand a lot of the stuff you referenced). A rough outline is fine. I'll punch it up and air it on the next show, and give you full credit for the help. We'll call it "The Halo Effect Revisited" or some such.

So I'll need your full name and town, too, and any creds you might have behind your name.

Write me at danhughesmail@gmail.com

Best,

---Dan

[ODM]

It's interesting to look up topics regarding grounding rods and the factors affecting their conductivity. Sometimes the corrosion needs to be artificially strengthened to decrease resistance, with use of various salts of copper, or noncuprous salts which help the copper corrode faster.

This is purely an assumption, but if the conductivity of an earthing rod is improved by the leeching of copper corrosion products into the soil, which increases its contact area (in a perfect circular example, square of radius multiplied by pi) with the surrounding earth moisture, these conductive corrosion products will increase the apparent area of the target.

I'll dig up a document or two on this topic and post them, I remember coming across an article with a study on the topic but I won't be holding any claims until I can find a study backing them.