Mystery Metal, Need Some Help!!

[dogodog]

Was out hunting a big field which has coughed up some decent finds over the last two years. The property has history from the 18th and 19th century. The day was pretty much a bust until my last signal a 55-56 on my MK, I thought it was an indian head penny because the numbers were close. Low and behold when I popped the plug I saw what looked like a hammered silver coin, Very thin, odd shape and then nope!!! What I found is what I thought to be a watch case back, But looking at it closer it seems to be a piece of jewelry? I also noticed stamping marks. So my problem is the odd numbers for silver. 

The item mic's at .035 or 1/32'' thickness, .945 or roughly 15/16'' long, .780 or roughly 3/4'' wide. It weigh's 2.65 grams, A silver dime weighs 2.38 grams. It has two stamped #13's on diagonal locations, And remnants of prongs for holding a stone. I did a little research and found the 13 assay mark could be German or Finnish, Pre 1886, In a roughly 800 purity. Question is does an 800 purity drive the numbers down. I ran tests with every weird metal and foreign coin I own and can not replicate these solid numbers. It looks like silver, feels like silver, weighs like silver. But I have my doubt's, Anybody have any clues? Not sure how to do a specific gravity test without it costing a lot.

[GB_Amateur]

SG test is pretty easy if you have a scale with sufficient precision (i.e. enough decimal places on the grams setting, which for this piece is 2).

1) weigh the piece by itself and record the result (in grams).

2) make a sling to hang the piece.  This could be wire (but make it as small diameter wire as possible) or thread.  (Don't use string since it will absorb and wick water.)  Make a hangar that sits on the scale and extends below the scale.  Think clothes hanger upside down.

3) put the hanger on the scale with sling attached and the item (your jewelry piece) in the sling.  Zero ('tare') the scale.

4) from below bring up a container of water and raise it until the item is completely submeterged (but not touching the bottom or sides of the container).  The scale will read a negative number.  That is the buoyant force and since the medium is water, the actual volume of the suspended piece in cubic centimeter units.

5) divide the result of step 1 by the result of step 4.  That is the density in grams per cubic centimeter or grams per milliliter.  It's also the specific gravity (unitless quantity).  (Don't be concerned by esoteric arguments of the difference between density in g/cc and specific gravity.  That's for snobs to nitpick over parts per thousand which are buried in the measurement uncertainty -- and the snobs aren't even aware of that!)

I assume the pieces wasn't much corroded or you would have told us.  I don't know how much affect on target-ID 80% silver would have compared to 90% or 92.5% but I'm sure our European members do.  I look forward to others chiming in on that.  Looks old to me, but I've been fooled before.

[dogodog]

Thanks for the info GB, I'll give it a try. I think I can mimic your description to achieve the results. (hopefully)

[dogodog]

I did the test, coming up with 7.507 gravity. Maybe tin or some weird stainless but I tested a couple of pieces of stainless with the MK and the numbers are not even close. Maybe Tin? I thought tin was very soft? I did test pewter and its still below that range. I would love to know the gravity of 800 silver.

Just did a bleach test and it stained the surface, Not sure how that reacts with tin, I'm still leaning towards some weird silver alloy. stumped for sure.

[kac]

Easiest way is a acid test kit. Looks like lower grade silver that was struck. There is a rim edge on either side. If the 13 is a purity mark then it must be some sort of decorative plate. Maybe to a clasp to a satchel or something along those lines.

[GB_Amateur]

12 hours ago, dogodog said:

Maybe Tin? I thought tin was very soft?

I think pure tin is soft (bendable) but what you have could be an alloy with mostly tin content.  Most alloys are harder/stiffer (one of the reasons elemental/pure metals are alloyed in the first place).

A lot of people (including detectorists) use the word 'tin' to describe steel cans, etc. coated in metal.  In earlier days (e.g. 19th Century), tin was the coating.  Just pointing out that you are referring to the element tin, not the common usage plated steel.

Tin was a valuable metal a few thousand years ago because when alloyed with copper it makes bronze -- a sturdy alloy, more sturdy than brass which is copper alloyed with zinc.  (Think 'Bronze Age'.)  I don't know how many centuries that value carried over and/or if it was used in jewelry.  But at this point I'd say you may be onto something.

I wish those XRF guns were affordable.  I'd be zapping ever detector find with it!

[JCR]

I found something similar on Sunday at a mid 1800's site that has no markings on the back and appears older. I too am trying to figure out what it is made of. I suspect Pewter, which has varied in formulation over time. Mine seems to have a higher Lead content than later pieces. I need to still research Britannia Metal. It still has some Silver plate/wash left on it. Yours could also be German Silver which has Nickel in it.

[kac]

Leaded pewter won't be shiny. Brittannia will have some shine but pewter doesn't have a smooth surface like that typically. I think it could be a low grade silver. Not sure what they add to silver to lower the grade.

Silver can be very soft but it hardens up when worked. People that spin or form silver have to constantly anneal it or it will crack.

[dogodog]

GB, I was thinking in the more pure form of tin. Back in the old days it was mostly used as a protective coating and also made tin coated sheet steel easier to solder. Being in historic restoration tin coated steel and such turns a grey color. Oh and it was banned a while back due to the lead content. I'm thinking we could go halfer's on a xrf gun? Even with the gravity test, the numbers just don't work. Seem's by the numbers it's closer to bronze.

JCR, Not german silver, I tested 5 different pieces of stock I have when making knives. Good call though. Actually it was the first thing that came to mind for me. I like the way you think!!!

$10,000 per person should get us a pretty decent hand held!!!! Including JCR

[kac]

Here is the pewter breakdowns, not much has changed over the years.

https://contenti.com/pewter-casting-metal-and-tin-alloys