Thursday, August 15, 2019

8/15/19 Report - Thoughts on Mystery Find. Metal Detector Conductivity Numbers and Object Identification.


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


I posted this item found by Jerry P. several days ago.  Jerry wondered what it might be.  He wondered if it might be an ink well, but I didn't mention that in my post because I didn't want to influence you.

Someone said they wish there was an object for comparison in the photo.  That might have helped.  Jerry did say that it is about three inches around.  If by that he was referring to the outside circumference of the object, it is small.  To give you some perpective, a US quarter is very close to three inches around.

I got a lot of different ideas on this object. Mitch K., who has been very accurate with his mystery item IDs, said it is probably a pet urn.

DJ thought since bronze is non-magnetic it might have been for a compass. He also thought maybe an inkwell.

Joe D. thought it would be too heavy for a snuff box, and thought maybe it held a clock or instrument.

On the ink well idea - I think that is a possibility, but if three inches is the outside circumference, it would be smaller than most. A three inch diameter would be more typical for an ink well. A typical ink well might have an opening with a three inch circumference but the pot would typically be larger than that.

Below is an 18th century ink well set that I found online. Motice that the pots are very similar to Jerry's item.




Below is a pewter pet urn.  Pet cremation urns come in a variety of sizes and shapes and are made of various materials.

Pet Urn.

Being an isolated find and having such a common shape, Jerry's item is difficult to identify.

Here, for another example, is a salt cellar.  It definitely shows some similarities to Jerry's object.

Salt Cellar.

Unfortunately I don't think we can say what Jerry's object is, although we have some good ideas for Jerry to consider.

One thing that I noticed is the clean uncorroded hinge on the object.  That doesn't seem to suggest a lot of age to me.  I'd expect to see more corrosion from a very old item coming out of the sea.

The owner of the object, knowing more about the circumstances of the find and being able to hold it, has the best chance of coming up with an ID.  He is now armed with a variety of thoughts on the subject.  Perhaps a mark or something will show up to provide additional evidence.

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As you know I have just started to explore the Equinox metal detector.  This morning I decided to do a few conductivity tests.  I used the same test area I've used many times before. The area is subject to various sources of electrical interference.  In fact today I started out in multi-frequency mode, but then it became noisy and I switched to 15kz, which was nice and quiet.

First I tested a zinc penny and a copper penny.  The zinc penny generally came up as 21 - 22 while the copper penny showed a conductivity of 25 - 26.

Then I tested a clad dime and a silver Roosevelt dime.  The clad dime showed very slightly higher numbers than the silver dime.  Both dimes were in the 24 - 27 range.  The silver dime might have been about one point lower on average.

Next I tested a clad aquarter and a silver quarter.  The clad quarter was around 28 - 29, and the silver quarter a touch higher, at 29 - 30.

The silver versus clad coin numbers in this test were too close together for me to draw any conclusions.  The zinc penny rang up lowest, and the quarter numbers were slightly higher than the dime numbers, while the copper penny was not very different from the dimes.

I also compared a 1967 to a 1964 half dollar.  As you might expect there was very little difference.  They were in the 33 - 35 range.

Then I checked a Morgan dollar, which showed in the 35 - 37 range.  So pretty consistently, the larger denomination coins showed higher numbers than the smaller coins even though there were differences in composition.

I also tested the two rings that I showed in recent posts.  One was the small silver turquoise ring and the other the small alloy Claddagh ring.  Both gave conductivity numbers of 24.

This wasn't an extensive or even good test.  I just wanted to get some ideas on how the specific conductivity numbers might provide helpful information, so it is too early for me to draw many conclusions.

The conductivity numbers definitely help some.  For example, you can certainly tell the difference between iron and most coins, for example, but when it comes to making more precise judgements, like the difference between clad or silver coins, I'm not so sure you can do that reliably using just the conductivity readout.  It does look like you will get a different reading for zinc and copper pennies.

People often conduct their metal detector tests with US coins, but I don't know how many people are out there looking for US coins.  I think most people are more interested in finding gold jewelry, old artifacts or other types of things.  Coins do provide convenient test objects, but one thing you probably really want to know is how your metal detector responds to the types of objects that you most want to find.

If you want to find gold jewelry, gold nuggets, silver reales, or old artifacts, the best test objects are the things most like those you want to find.  If you are after gold rings, for example, be sure to test your metal detector on a variety of types and sizes of gold rings.

Many of us hunt a variety of types of objects.  That means that you should become familiar with how your detetor responds to a wide variety of types of objects.  Want to find a Rolex watch?  I'd suggest testing your detector on watches.

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One person hoped that Glen would keep us informed about any progress he makes on his mystery object, for example if he cleans it or gets it x-rayed or finds anything else that might be related.   When people contribute their ideas they are interested and have a little investment in an object, they would like to know what happens next.  When I take the time to answer a question for someone, I hope they let me know of any additional developments.


Expect a few more days of calm surf.  There are not storms forming yet.

Happy hunting,
TreasureGuide@comcast.net