Written by the Treasureguide for the exclusive use of the Treasure Beaches Report.
I've been conducting a few crude tests on coins. Lately I've been using silver coins made of 40% to 90% silver, as well as clad coins. The last test I did with the Equinox metal detector produced no difference in conductivity readings for a 90% silver quarter (1923) and a clad quarter (2002). Both produced conductivity readings of mostly 29, with an occasional 28 or 30.
I was expecting some difference between the quarters as a result of my tests on half dollars, which showed a two or three point difference between a 40% half dollar coin (Kennedy) and three 90% half dollar coins (a Franklin and Walking Liberty). Those results need to be replicated by better studies.
Anyhow, I decided to see if the electrical conductivity of the metals used to make the coins accounted well for the conductivity readouts obtained by the Equinox metal detector. Below you'll see a chart giving the electrical conductivity of a large number of metals.
As you can see, silver has the highest conductivity of those metals. Silver, copper and gold are the three most conductive metals listed on the chart. The electrical conductivity of those metals seems to account fairly well for the conductivity readouts obtained by the Equinox.
Maybe a big part of the reason the Equinox produced the same numbers for the silver and clad quarters is that the major metals making up those coins have a very high conductivity. And although the clad quarter contains nickel, which is a less conductive metal, the amount of nickel in that coin is just over 8%, while copper makes up about 92% of the clad coin. So although the silver quarter was made of 90% silver and the rest copper, the clad quarter was made mostly of copper, which is nearly as conductive as silver. Just looking at the table, it seems reasonable that there would be very little difference in the readouts. Based solely upon composition, the clad coin should be slightly less conductive. It would be so close, though, that it is not shocking that the Equinox did not show a difference.
From experience, I know that nickels, (even Buffalo nickels) usually give a reading of 13, which is a much lower number than what we've seen for the quarters and half dollars that I previously tested. The Buffalo nickel is 75% copper and 25% nickel (a larger amount of a much less conductive metal), so that makes sense.
The Kennedy half dollar coin was 40% silver and 60% copper, while the other three half dollar coins I tested were 90% silver and 10% copper. The reading I got on them was something like 31 - 32 for the Kennedy and 33 - 34 for the others half dollar coins.
Comparing the 90% silver half dollar with the 90% quarters, the half dollars gave conductivity numbers that were about 4 points higher than the quarter on the Equinox even though the proportion of silver and copper were the same. That suggests that size matters as well as composition. Other things might also affect the results.
From my few crude observations, it seems that the relationship between the conductivity numbers produced by the Equinox are related to the electrical conductivity of the metals that make up a coin, but it does not seem to be a simple linear relationship, and there seems to be some additional factors.
All that said, target ID and the decision to dig a signal should not be made solely on the basis of the conductivity readout. Consider your goals, previous knowledge of the site and the prevalence of different targets and their values, and all other information you might have. I've done previous posts on decision strategies.
Below is the chart of electrical conductivities for many metals.
Conductivity and Resistivity of Metals
Material | Resistivity | Conductivity |
|---|---|---|
| Silver | 1.59x10-8 | 6.30x107 |
| Copper | 1.68x10-8 | 5.98x107 |
| Annealed Copper | 1.72x10-8 | 5.80x107 |
| Gold | 2.44x10-8 | 4.52x107 |
| Aluminum | 2.82x10-8 | 3.5x107 |
| Calcium | 3.36x10-8 | 2.82x107 |
| Beryllium | 4.00x10-8 | 2.500x107 |
| Rhodium | 4.49x10-8 | 2.23x107 |
| Magnesium | 4.66x10-8 | 2.15x107 |
| Molybdenum | 5.225x10-8 | 1.914x107 |
| Iridium | 5.289x10-8 | 1.891x107 |
| Tungsten | 5.49x10-8 | 1.82x107 |
| Zinc | 5.945x10-8 | 1.682x107 |
| Cobalt | 6.25x10-8 | 1.60x107 |
| Cadmium | 6.84x10-8 | 1.467 |
| Nickel (electrolytic) | 6.84x10-8 | 1.46x107 |
| Ruthenium | 7.595x10-8 | 1.31x107 |
| Lithium | 8.54x10-8 | 1.17x107 |
| Iron | 9.58x10-8 | 1.04x107 |
| Platinum | 1.06x10-7 | 9.44x106 |
| Palladium | 1.08x10-7 | 9.28x106 |
| Tin | 1.15x10-7 | 8.7x106 |
| Selenium | 1.197x10-7 | 8.35x106 |
| Tantalum | 1.24x10-7 | 8.06x106 |
| Niobium | 1.31x10-7 | 7.66x106 |
| Steel (Cast) | 1.61x10-7 | 6.21x106 |
| Chromium | 1.96x10-7 | 5.10x106 |
| Lead | 2.05x10-7 | 4.87x106 |
| Vanadium | 2.61x10-7 | 3.83x106 |
| Uranium | 2.87x10-7 | 3.48x106 |
| Antimony* | 3.92x10-7 | 2.55x106 |
| Zirconium | 4.105x10-7 | 2.44x106 |
| Titanium | 5.56x10-7 | 1.798x106 |
| Mercury | 9.58x10-7 | 1.044x106 |
| Germanium* | 4.6x10-1 | 2.17 |
| Silicon* | 6.40x102 | 1.56x10-3 |
Source: Electrical Conductivity of Metals (thoughtco.com)
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These days we see too many examples of powerful evil people making misguided decisions that end in unnecessary death and ruined lives. Here is one example. We have tragic examples from the Ukraine, Canada and the United States.
Matthew Lawrence Perna, Sharpsville, Ohio Obituary (wkbn.com)
Really sad. Stand against evil.
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| Source: MagicSeaWeed.com. |
A somewhat bigger surf is expected tomorrow. The tides aren't bad either.
Happy hunting,
TreasureGuide@comcast.net