7/18/18 Report - Old Silver Ring Stolen. Test of Metal Detector On Silver Coins.

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

Stolen Ring Thought To Be 1700s Era.

I decided to do a little test using the Garrett Ace 250.  I'll use other detectors in the future, but decided to start with a common and inexpensive model.

For test objects I decided to use coins that were close in size, weight and composition to Spanish reales.  I used a silver dime, quarter, half dollar and peace dollar - all of 90% silver.

The diameters were 17.91, 24.26, 30.6 and 38.1 millimeters, which is close but not exactly like one, two, four and eight reales.  Just as an example, the silver dollar is 38.1 mm and the eight reales would be about 38 mm.  Pretty close.

The weight of the silver coins is 2.59, 6.259, 12.59 and 26.73 grams.  Again, that is close to the weights of the Spanish colonial one, two, four and eight reales, which varied to some extent for a variety of reasons.

The diameters and weights of the coins used in the test are highly correlated.

The vertical scale is diameter in millimeters and the horizontal scale is weight in grams.

The correlation is naturally high, but as you can see the relationship between diameter and weight is not linear.

The similarity of the modern coins and Spanish colonial coins in both size and weight is not accidental - the American coinage being pretty much based upon the Spanish.

I did what I would call a ground test in an area with virtually no mineralization but some amount of ambient electrical interference.

Coins were placed on the ground and the height of the coil that continued to produce a good steady signal was measured.

The dime was detected at approximately 7.5 inches, the quarter at 8.0 inches, the half dollar at about 8.5 inches and the Peace dollar at 9.5 inches.

Depth approximations were not highly precise.  Results were also specific to the location and environment.

Depth detectected relative to coin weight.

Depth detected relative to coin diameter.

Coin weight and diameter are highly correlated, which makes it difficult to tell which is most important, but I have previously found and stated that surface area is more important than the weight of the object in determining how deeply a coin will be detected.  The surface area of the coin, however, is not as important as the presented surface.  By that I mean a coin with a large diameter, if tilted or on edge will not have as large a surface area relative to the position of the coil and therefore will not be detected as deeply.

Given the number of variables and the lack of precise measurements, the results should be taken as only approximations.

All-Metals mode and maximum sensitivity was used during the entire test.

Spanish cobs are all so different that I thought the silver U.S. coins would be more useful as test objects and allow more comparisons and generalizations.  Beach recovered Spanish cobs are all of different sizes and shapes.  As I've reported, they can be less than half the minted weight and are of different shapes.

It should also be noted that the depth was measured when the object was under the center of the detector coil at near optimal sweep speed.  When the object was closer to the edge of the coil, depth was less.  And if a less optimal sweep speed was used, depth would have been less.

I've commented at length on the limitations of both air and ground tests.

In the future I will be conducting more tests with other metal detectors.

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I received an email reporting the above ring stolen during a club meeting.  The owner would like it back.

That, by the way, is another good reason to keep good records on your finds.

Most detectorists go out of their way to return lost items, but like with any group of people, there are some bad apples that spoil it for everybody.

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A lot of people are still reading my old Cooper's Treasure posts.  I don't even watch it.

There is no tropical cyclone in the Atlantic.  The surf is up a foot or two.  The tides are still pretty good, but lessening slightly.

Happy hunting,
TreasureGuide@comcast.net

6/23/16 Report - Testing Metal Detector With Various Small Reales. North Carolina Beach After Nor'easter.

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

North Carolina Beach After a Northeaster
Source: Video link submitted by Gosports shown below.

As I showed a day or two ago, the Treasure Coast didn't get much erosion from the higher surf. Gosports1 sent me a link to some YouTube videos he posted showing what happened to a North Carolina beach after a Northeaster back in April.  This shell layer goes for hundreds of yards.  He'll be sending some find photos before long.  Take a look at his short videos on YouTube that show more of this beach. 

 https://youtu.be/tpXhqApWmLU

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I'm never sure which posts people like the most.  The most "google plussed" posts are often not the most read posts.  For example, when CNN Travel interviewed me they posted a link to the blog.  That resulted in tons of readers for the most recent posts at the time.  I don't think those posts were the best, but more people read them.

So far this month the 6/8/16 Report -  Treasure Coast Treasure History: Cobb Coin VS Unidentified Wreck.  2000 Year Old Cache of Hasmonian Coins was by a substantial margin the most read.

Some posts result in more emails.  I take that into account, but sometimes it is just because a particular post connects with certain readers for some reason.

A lot of web sites just want a lot of hits so they can sell things.  It doesn't particularly matter to them how valuable the posts are as long as people visit the site and see the ads.

I have my own favorite posts.  Sometimes they don't get much visibility - not as much as I think they should.  Sometimes they are posted on a holiday or slow time or some big news comes up that overshadows them.

I decided to occasionally post again some of the posts that I really thought were good but that maybe didn't get enough visibility.

Here is the first.  It was originally posted nearly two years ago on 8/30/14.  I'll call it a rewind.

Now I'm going to pick up today where I left off yesterday.  I'm going to show you something new that might surprise you.  It also shows how specific you have to be about detector tests, particularly the types of targets you are interested in and the environments they are used in.  A number of factors have to be considered when selecting a detector for a particular job.

A lot of people seem to accept what they hear or accept the results of simple tests on clad coins that actually leave out a lot of important factors.  They think if detector A is a good detector or has a good reputation it is the detector to use.  The fact is, as I'll show today, it is much more complicated.  And as I showed yesterday, there are situations when an inexpensive detector will actually do a better job than a highly regarded more expensive detector.  The basic questions are, what do you want to find and where are you going to hunt.  I say those are basic questions, but to answer them well involves more factors than you might think.

If you haven't read yesterday's post yet, I recommend that you do that before continuing.

Here are the same small beach cobs that I used for the tests that I reported on yesterday.  The one on the left weighs about 0.4 grams, the next 0.5 grams, the next 0.6 grams, and the next 2.0 grams.  I will refer to these cobs going left to right as 1 - 4.



Four Treasure Coast 1715 Fleet Beach Cobs.  Three Half-Reales and One 1-Reale.

Yesterday I tested these in a high EMI environment using the Ace 250.  Today I'll report on my results using an Excalibur.

I used both discrimination mode and pinpoint mode for all my Excalibur tests.

Which cob do you think consistently produced the best (loudest and clearest) signal?  It was cob 3.  You might expect it to be cob 4.  I did.   But cob three consistently produced a signal that was a loud and distinct, and a slight bit better than cob 4.  That was true on many attempts varying the sweep speed, and sweeping at different directions.

Tests were done with the coil at the approximate same height over the cobs, and also at different heights to give a rough measure of depth.  By varying the height of the coil I essentially did a type of air test but with a sugar sand background and relatively high EMI environment.

In case you wondered, signal loudness and distinctness correlated with air-test depth.  In other words, cobs that produced a fainter signal when the coil was at the same height for all cobs, were detected only at smaller distances from the coil.  Those cobs that produced louder more distinct signals were detected at greater heights when the coil was raised.  So relative signal strength, as you might have suspected, is a decent (not perfect) measure of how deep a target would be detected.  That makes sense, but the test results did strongly support that conclusion.

Now the question is why did cob three, even though smaller by weight and presenting less surface area produce a louder signal.   I do not yet know.   Yesterday I suggested that one possibility could be different alloys or composition of the silver.  We know that the composition of cobs was regulated,  but we also know that there were some differences.

Surprisingly, cob 1 consistently produced a more distinct signal than cob 2 despite its smaller surface area.  It is thicker.  All other cobs produced better signals than cob 2 without exception.

Another reason could possibly be the ground under the cobs, but I changed where I did the tests and the results were the same.

The results did not change when I switched from discrimination to pin point mode.  

I often hunt in pin point or all metals mode.

Ordered by signal strength, it was cob 3, 4, 1 and last, 2.

Being in a high EMI environment, I varied my sensitivity.  I actually got slightly better signals with reduced sensitivity.  

Some people are afraid to reduce sensitivity.  I seldom reduce sensitivity and am accustomed to identifying signals in noise, but there are times to do it.

I always recommend testing your detector and settings with the type of target that you want to find and in the environment that you will be hunting before beginning to hunt.  I think these tests support that recommendation.  Things are not always simple, and if you want to optimize your detector and settings, do it in the environment and with the most desired targets.

When selecting a test target, Id select a smaller test target.  Generally if you are set for the smalls, you will find the larger targets too, whereas the other way around is not necessarily true.

A lot of people are running around with detector settings that would not detect the smaller cobs shown above if the cobs were laying on the surface with the detector coil right over them.  I know I have met people on the beach who were discriminating out anything that small.

As I showed yesterday using the Ace 250, these test cobs generally were identified as nickels.  That's not bad.

The best way to learn how to better understand and use your detector is to experiment.  What you read may or may not be true, and your detector and your environment might not be the same as those you read about.  

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I haven't gotten around to promised post on shells and sand yet.  It is not easy to make it clear, but I will get it done, hopefully before long.

Not much has changed on the Treasure Coast.  We'll have a one to two foot surf for several days.

There is no tropical activity to watch.

Happy hunting,
TreasureGuide@comast.net