test garden

[time4me]

Well, I've been metal detecting for about 30 years or so now, and definitely ALOT in the past 10 years, but I've never tried creating a test garden.

I've been mainly using my Minelab Explorer II for the past year, and recently I've been trying to get used to the E-Trac. I've been as much as I can about the Explorers and E-Trac to try to improve my skills with the machines, and I finally decided to bury a couple of coins to see what the audio and visual responses would be like on deep silver.

I buried a silver washingon quarter at 8 inches, and a silver rosevelt dime also at 8 inches.

Man am I ever disappointed. I can't pick up the dime with any of my detectors - Exp II, E-Trac, Whites Eagle Spectrum, or my son's X-Terra 70 or Garrett Ace 250.

The silver quarter I can pick up best on the Exp II in Iron Mask mode with the sensitivity cranked up a bit. The Exp II definitely picks it up better than the E-Trac. Surprisingly, the Ace 250 does a hell of a job picking up the quarter and gives a very consistent and repeatable "bong, bong, bong" when going over it.

So my question is this... Since I just buried these two coins yesterday, should I expect a "halo" to form over time, making them easier to pick up with my detectors? I know everyone always talks about the "halo" or "ground matrix" effect on coins and other items buried for 50 years or more, but I have no idea if there is any truth to the "halo" theory, or how long I need to wait for the "halo" to start forming.

My experiment was successful in one way, as I now have a better understanding of what I've been reading about the "cursor bounce" on the Explorer II on a deep silver coin.

Has anyone else had similar experiences and frustrations in setting up a test garden?

Jim

 

[Charlie P. (NY)]

My test garden is a '79 cent at 8", a '70 cent edge-on at 8", a 0.715" musket ball at 12", a silver quarter ('63D) at 12", a clad quarter ('83) edge on at 12", a cent just under the surface (2006) a pull tab at 2" with an '81 cent 1" to one side and 6" deep, a nail at 2" with a '76 cent 1" to one side at 6", a '91 nickel at 7", an '88 dime at 6", a shotshell base at 5", three different styles of pulltabs at 5" and an aluminum screw-cap at 4". All seperated one foot and marked with various colors of plastic gold tees.

There are days I can get good readings with all targets using both my Musky and my F-75. Some days I have trouble with either on the 12" targets. Those have been buried three years now. Whether a halo ever occurs is debatable (I believe) but certainly the soil evens out after having been disturbed to dig the hole and bury the test targets. IMHO the presense of the coins does have an effect on the surrounding soil - either catalytically without degrading the coin or through electrolysis/ion transfer with the salts in the surrounding soil. Large or measureable? That I can't say. But disturbed soil CERTAINLY ground balances differently than undisturbed soil so a long buried coin is in a more even surrounding matrix than a freshly buried one - possibly defeating some of the detectors "senses".

PS - The test garden targets with the pull tab and nail over the coins are good practice targets. You can see the benefits of "X"ing over questionable targets and test your detectors iron mask.

 

[Jim Hemmingway]

Hi Time4me,

I wouldn't be too disappointed with your test garden results. Your results are fairly typical for many units on freshly buried targets (disturbed ground). Some units will perform better than others in this scenario. All units that I've owned will do considerably better in undisturbed ground wrt depth, target ID and discrimination.

In my test plot (Spectrum XLT ground phase @ -93.2 and 0.1% magnetite on the F-75) with higher mineral ground, none of my units will target ID/disc beyond roughly 3 and 1/2 inches with any accuracy; once beyond 4 1/2" to 5", most coins read as iron. Depth (solid, two-way repeatable signals) varies with each unit, but generally between 60 to 75% of undisturbed ground depth.

One exception is the F-75, which similar to Charlie P's, will get very close to air test depths, although with a more modulated signal. Maybe on the order of 85 to 90% in my ground...and that definitely varies a bit with soil moisture. I don't expect it will do much better in undisturbed ground, as I do not believe this unit over any ground can surpass it's air depth.

By contrast, the Spectrum XLT somedays will get 6" on a penny, other times I can just get a reading on the 4" penny in the test plot. I know I've dug pennies routinely at 6" and occasionally at 7" in undisturbed ground. Not many, but enough to know it's depth capability.

I don't know if your test garden will "ripen" and eventually mimick undisturbed ground depths. I had a 12 year old test plot that never did ripen. Others claim theirs do. Some knowledgeable hobbyists recommend adding salt water into the holes when initially placing the targets, as it would seem the brine enhances the "ripening" more quickly to comparable undisturbed ground depths.

I refer to increased depths observed in undisturbed ground compared to disturbed ground as "undisturbed ground effect". Whether increased depth/improved target ID/disc performance in undisturbed ground is a result of halo formation, less scattering of electromagnetic field, or electrical alignment of ground charges, or as described by Charlie above...is neither here nor there, and certainly not worth any debate. Whatever the reason, "undisturbed ground effect" is a very real phenomenon that few would debate.

Test gardens have their use as long as we realize the limitations. Certainly, test plots allow the user to simulate what might be expected when detecting over ploughed/cultivated fields, or other areas of looser/unconsolidated material. If I want to evaluate a prospecting units depth capability prior to purchasing, there is no choice but to bury different size nuggets in a "test plot" and see which will perform best in that ground.

That's my nickel's worth. Take care and HH

Jim.

 

[Lowbatts]

Back quite some years ago, I found my first 8" coin target. A very nice looking SLQ that had a clearly repeatable signal. For curiosity' sake I dropped a clad quarter in the spot where the SLQ had lain for many decades. The immediate ground around the coin had not been disturbed as I had dug a plug first and then popped a clod to the the right point fortunately.

Replaced the dirt and plug and could not get that coin to signal in disc mode at all. Purely anecdotal and unscientific I'm sure because it neither confirmed nor denied any ideas I had about "halo" or ground mineralization, since I didn't have any. I just thought it'd be a neat test or something like that.

But I do think test gardens are important places to learn about pinpointing skills, just seems it's easier to learn pinpointing with visible targets.