Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.
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| 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.
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| Depth detectected relative to coin weight. |
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| Depth detected relative to coin diameter. |
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
