Us Pennies Composition, Weights & Tid's For The Ctx3030 & Etrac

[maxxkatt]

Ever wondered why pennies ring up so differently? Well you probably knew, but here are some more detailed results tested on the CTX3030 in the Ferrous-coin mode with the pennies on a patch of ground cleared of any other metal.

You can easily see from the data that the TID values change when the composition or weight changes.

 

[GB_Amateur]

I assume when you say '0.25' in the tin and zinc columns you mean 0.025.  I'm curious where you got these numbers.  The tin&zinc numbers you show are inconsistent with what I've found for the Lincoln series.  I'm also curious as to what coins you used to determine the CTX3030 dTID's -- were they dug coins or undug?

I've been unable to find the tin&zinc breakdown for the bronze Indian Heads.  See post I made a week or so ago for the Lincoln Cent compositions by year with referecnes, some of those detailed in earlier posts in that same thread:

 

[PimentoUK]

US coinage is not my field, but the metal compositions are definitely not correct in that table.
Wikipedia has a summary of their alloys:
https://en.wikipedia.org/wiki/Penny_(United_States_coin)

 

It would be educational if you tested a circulation Indian head coin ( not a dug-up ), to give a baseline figure for how high they can read ( conductivity ) , then the drop in reading due to corrosion becomes clearer.
We have similar bronze coins here in the UK, and the drop in Co value due to corrosion is marked, and very variable.

[GB_Amateur]

I'm on it next week!  (With the ML Equinox since I have no CTX3030 -- more meaningful to the masses = po-folk, anyway.  😁)

Glad to hear someone reliable report on dTID changes from bronze coins that have been in the ground (compared to those never suffering that treatment).  It's something I've suspected for copper alloy coins in general (so including Cu-Ni coins) but have yet to confirm.

[PimentoUK]

Our big bronze predecimal penny ( 1860 - 1967 ) reads TID=80 on the Fisher F75 when fresh, sort of where you would think it belongs. But 50+ years of rot, and they're typically reading 55 - 65 TID. I have dug a couple that had ID pretty much right, one was a last issue '67 in a park that may have had fresh topsoil added, so probably lacking in typical farmland fertilizers/animal excrement/urine chemicals.

 Curiously, our cupro-nickel coins seem little-affected by corrosion. They look awful, and clearly have been pickled, but the TID drop is minimal. Maybe it's because CuNi is a lousy conductor to start with, so can't get much worse? Our oldest CuNi coins are 1947, they're mostly near-identical alloy to your US 5c coin.

[dogodog]

GB, if you do some testing on the IH's, Please compare dates. Say 1884 dug vs collected. I have long believed that penny's especially IH's depending on date have a wide range of metal composition. On my 800 they can dip as low as 17 and as high as 24. On my Tesoro's the disc. break can be all over the place depending on year of the coin. I think our government didn't care to much about the penny standard of metallurgy. I think they were all over the place with metals and only focused on the weight. I've done some testing myself and still can not understand why the difference on dates so close together. Generally if I hunt IH's I hunt at a starting disc and go back at a later date and adjust for the odd ball dates I can not find. Seems to work for me since I'm not in any big hurry. This is a great topic and can't wait to see the results.

[Joe D.]

Interesting topic! 

   Thanks all for posting! And Dog, great info about differing composition on IH's; make's sense! I never would have considered that, especially since there are few to be found down here!👍👍

[GB_Amateur]

1 hour ago, dogodog said:

I think our government didn't care to much about the penny standard of metallurgy. I think they were all over the place....

I've seen this argued previously but it is inconsistent with what I've read about the US Mint.  The only 'out' is that they may have allowed the tin/zinc ratio to vary when purchasing bronze sheets, but the 95% is locked in.  In the case the Lincolns the tin & zinc components were sprecified but I have been unable to find evidence for either side (consistent or variable composition) for the IHP's.

A good read on how well compositions were able to be measured can be found with the early California Gold Rush assaying, such as Kagin's book shows (kind of expensive if you have to buy it -- check the library).

Very early on (first 15 years or so, up to around 1810) the mintage of coins was less precise although I don't know if that imprecission spilled over to composition.  After that it was quite consistent in general.

Good idea to measure both dug coins and undug, and I'll do that as best I can based upon the dates I have access to.

[oneguy]

Those chart #'s may or may not be "accurate" but , if not?, they are close enough to get the point across about the differences in target responses to different types of pennies.  I no longer coin shoot but back in my etrac days my IH penny #'s all but came to a stop compared to my 22yrs swinging a Tesoro.  Reason being my Tesoro didn't give me much info, if it beeped you dug so the IH's came, along with everything else (crap).  With the etrac I had tons of info to aid me in deciding to dig or move on.  As I was more into deeper older coins and already had a good collection of IH pennies from the Tesoro days I didn't really care to dig them although etrac got a few.  On the etrac the IH's ring up there real close to the zinc penny #'s.  My time is valuable whether coin shooting or nugget shooting so to manage my time better on coins I quit digging IH and zinc #'s.  I'd leave all the zinc for the "other" guys...lol but sacrificed a few IH's in the process, no biggy.  This chart is a good thing for those folks maybe not up to snuff on coin content and/or might care to manage your dig time to focus on what you really want to find?  I used to laugh to myself a lot about leaving all the zinkers for the rest of the crowd.....lol

Good job on the chart....!!!!!

[dogodog]

GB, I'm thinking you might need to break down and purchase an XRF or subject your prize IH's to the dreaded OES test. Nothing like a vaporized piece copper alloy.  Either way its for the good of Detector Prospector and its loyal members. Ha Ha