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The 1821 Zacatecas 8R Surface Phenomenon Coin Cleaning Puzzle/Dilemma

 
 
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 Posted 08/14/2019  09:09 am Show Profile   Check colonialjohn's eBay Listings Bookmark this topic Add colonialjohn to your friends list Get a Link to this Message
When Robert Gurney came out with ground breaking book on Counterfeit Portrait 8 Reales I decided to fly down to the MNA (Second Annual Mexican Numismatic Association Meeting) in Arizona to meet him in person and help promote the book. Making a long story short this fellow comes up to me and compliments me on the book but then said "How about the 1821 Zacatecas 8R issues - What is going on with the surfaces of this issue? I thought Bob and yourself would address this issue?" Are some of these counterfeits due to their STRANGE appearance? At that point I had to admit I did not know much of these issues but did agree with him in upper grades (AU & better) some 8R examples (not all) had non-homogeneous looking surfaces. See this example that I purchased from a recent Stacks/Bowers auction which is a very good example of my point here with non-homogeneous surfaces.

Here is the SB auction link:

https://auctions.stacksbowers.com/l...erly-cleaned

If we look under a stereo microscope under 20-40X power magnification we see in certain letters deep in their devices salt crystal build-up which I believe due to their white appearance to be AgCl. Notice also white/dark bands throughout in the fields and devices. There is no signs of dipping or polishing just regular marks under stereo microscopic review (i.e., no circular hairlines just intermittent contact marks in a haphazard fashion). BTW IMO the coin is UNC but probably reduced to AU in the belief the coin was improperly cleaned. I mean ... to a third party grader and most people a non-uniform surface obviously means its been cleaned. Unfortunately I am retired now so I do not have access to a SEM/EDS device which would allow me to identify the COMPOUNDS on the surface and core (I would cut this coin in half and do a core to surface check). XRF would only yield the metal percentages and as some of you already know Sulfur and Chlorine are the two most common outside contaminants on the surface of ANY coin which then promotes their toning in most cases - particularly sulfur with copper in this alloy example. If we read about the Haciendas using mercury amalgamation and smelting TOGETHER the darker ores or negro type ores had high sulfur and the preferred process was smelting as mercury amalgamation did not work well on these ore types but just ores with high AgCL type ores. Making a long story short again I will be presenting a paper to a group in September going through the chemistry. I believe this being 1821 the year of Independence and due possibly to a lack of copper sulfate, iron and/or mixing both dark and light ores and only using mercury amalgamation. So my THEORY and you can check most 1821 Zacatecas 8R issues for sale every week in AU or MS grades - ask these questions: Why do most have these irregular light/dark banded areas? Under a 10X-15X coin loop review what are these crystals and powdered areas present in the protected areas of the coin? Its my belief and someday I may do it are the light areas non-reacted AgCl areas and the darker areas non-reacted AgS areas? As hard as it may be for some to grasp now I am 99% certain this NGC label should read "MS63 Incomplete Mercury Amalgamation Surfaces". It would be very simple to prove using metallography and SEM/EDS techniques to confirm the coin has high areas of AgCl, AgS and Hg2CL2 which is poorly annealed mercury amalgam during the silver cake final treatment process. So to answer NOW the MNA # 2 Conference inquiry - yes I believe these issues have been INCORRECTLY classified as CLEANED and this discoloration has simply to do with poor amalgamation on high sulfide ores or having a lack of certain materials like iron and copper sulfate to assist in this Hg amalgamation process due to these times in Mexico's history (i.e., 1821). I do not believe these are later counterfeits in any way.

John Lorenzo
Numismatist
United States
Edited by colonialjohn
08/14/2019 09:20 am
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 Posted 08/14/2019  9:08 pm  Show Profile   Bookmark this reply Add jgenn to your friends list Get a Link to this Reply
Thanks for the interesting write-up, colonialjohn! And congratulations on your retirement -- I hope it was voluntary.

Were you able to examine the coin through the plastic or did you have to remove it from the slab?
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 Posted 08/15/2019  12:20 am  Show Profile   Check colonialjohn's eBay Listings Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
My retirement was at 62 - voluntary. The coin remains a mystery as I do not have access to a SEM/EDS device a much more sophisticated device than an XRF machine whether a gun type or even a more accurate bench top model. XRF will only give individual metal quantitative values which will do no good here as all coin surfaces contain chlorine and sulfur to some degree. SEM/EDS will map out and confirm non-amalgamated AgS, AgCL and Hg2CL2 compounds on the surface and in the coins interior if cut in half. I believe this coin to be IMPROPERLY mercury amalgamated leaving these compounds in the refined silver creating these non-homogenous surface conditions on many 1821 Zacatecas 8R issues which are plainly visible ... more so of course in high preservation condition (i.e., AU or higher).

JPL
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 Posted 08/15/2019  07:25 am  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply
I would wonder if you could get someone at a Mexican university interested in this project.

If I recall, I've read some papers where SEM/EDX was used to analyze the dark spots on modern gold coins, so there are places carrying out this kind of investigation.
But you probably know more about this than me.

Edited by tdziemia
08/15/2019 07:26 am
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 Posted 08/15/2019  2:22 pm  Show Profile   Check colonialjohn's eBay Listings Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
Yes I did read that paper on what causes the dark spotting on modern gold issues ... its AuS compounds. Most sulfur bearing compounds are DARK. That again is why SEM/EDS is needed it will yield what I suspect are these IMO ... INCOMPLETE UNREACTED silver compounds (AgS, AgCL and Hg2CL2) with the mercury amalgamation process in the alloy mix. XRF would only tell me the surface is showing very high sulfur and chlorine - interesting but then you could argue their presence is primarily environmental contamination.

JPL
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