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241-238bc Libyan Revolt Arsenic Coins? Please Let Me Know What You Think.

 
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Pillar of the Community
United States
546 Posts
 Posted 04/22/2021  01:59 am Show Profile   Check casualcoincollector's eBay Listings Check casualcoincollector's eCrater Listings Bookmark this topic Add casualcoincollector to your friends list Get a Link to this Message
So, I came across this old article recently from 1989 about the arsenic alloy coins of the Libyan Revolt 241-238BC:

https://www.researchgate.net/public...ibyan_revolt

And I think that I may have been able to procure a few examples that may be contenders to be the coins that they are talking about. Photos below. I don't have a way to test if they have an arsenic content or not but based on their individual weights I believe that there is a pretty good chance that these pieces must have a high arsenic content.

They all appear to be to light in weight to be made of regular tin based bronze or copper (weights listed with each coin). Arsenic is a bit less dense then copper at 5.72 g/cm3 to coppers density at 8.96g/cm3 and when I use a US pre 1982 copper cent for reference at 3.11g it seems to me that these coins must be made of something significantly less dense then copper or tin based bronze and thus must have a high arsenic content to compensate for the weight difference but I am by no means an expert in ancient coins. So, I would appreciate your thoughts on the matter and please let me know if you have any question for me. Thanks.

Coin #1:





Coin #2:





Coin #3:



Edited by casualcoincollector
04/22/2021 02:08 am
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Canada
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 Posted 04/22/2021  07:57 am  Show Profile   Bookmark this reply Add oriole to your friends list Get a Link to this Reply
I think that it is pure speculation unless you have some more substantial evidence.

1. You can do a density test with a good scale that measures to at least 0.01 grams.
2. If this passes then it might be worth pursuing an XRF test which would indicate if there is any significant arsenic.
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19236 Posts
 Posted 04/22/2021  08:29 am  Show Profile   Bookmark this reply Add Spence to your friends list Get a Link to this Reply
I agree with @oriole, but would only add that if you have a local college or university with a science department, you might be able to work with a professor on using SEM/EDS to look for that Arsenic (as was done in the article you cite).
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 Posted 04/22/2021  09:08 am  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply
Very interesting hypothesis, and thanks for the link to the article.

A couple of reactions, but maybe take it with a grain of salt since I don't own a single ancient coin:

1. It is clear form the paper that the arsenic alloys look significantly different from either bronze or silver. I am not sure from your photos if all of yours fit this description, but it looks like some do.

2. While the paper is disappointing in NOT giving any composition data for the bronze coins in the hoard for reference (or any density data at all!), I don't think a density measurement will help you because the paper shows that there are wide ranges in composition of the copper-arsenic types (for instance, "core" composition ranging from 81% copper to 96% copper), as well as casting voids that would affect density. Possibly any light feel to the coins is due more to this than to composition?

I tend to agree with @oriole that the only way to check your hypothesis is to find a coin dealer/jeweler who would do XRF on your coins, with an arsenic value over 5% giving a high confidence that you're hypothesis is correct.

(Added after seing @spence's comment: yes, or SEM/EDX, though this might be tougher to find)
Edited by tdziemia
04/22/2021 09:11 am
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Australia
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 Posted 04/22/2021  10:05 am  Show Profile   Bookmark this reply Add sel_69l to your friends list Get a Link to this Reply
Small wonder the Libyans revolted! - They would need to be near a toilet, even with occasional handling of those coins!

If a Cu/As homogenous alloy, XRF would definitely detect As in the surface layer.
Your nearest bullion dealer or scrap jewelry buyer should have a hand held XRF instrument.
The ancients would have had no idea how to refine out traces of As, in what was otherwise would have been perceived to be an innocent bronze alloy.
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Some early Australian Sydney Mint gold sovereigns in the 1860's had traces of naturally occurring arsenic in the alloy, which made the coins brittle, and could not be issued into circulation. Sample coins were sent to The Royal Mint in London for destructive chemical analysis. No XRF in those days.
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