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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
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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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 Posted 08/30/2019  3:22 pm  Show Profile   Check colonialjohn's eBay Listings Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
So my point is these darker areas in my opinion are sulfur bearing. Being mixed in with the lighter areas (AgCL). Its well known in the Hacienda silver producing manufacturing arena in New Spain darker or negro/negrillo ores were the ones containing sulfur and these are roasted with salt (NACL) or mixed with copper sulfate to silver chloride (white color) then AgCL could be mercury amalgamated. The lighter color ores were assumed to be predominatly AgCL already. This is important when looking at the surface of the Stacks coin. If my assumption is correct and this discoloration reaches the core of the coin (if cut in half and analyzed by (SEM/EDS) this could SUGGEST since this surface phenomenon appears in almost a 1/3 of all 1821 Zacatecas 8R issues in AU or higher slabbed or not slabbed this could be a situation in 1821 the year of Independence POSSIBLY negro (AgS) ores were not roasted with salt PROPERLY (or not at all - for whatever reason) in some silver ore lots and were simply amagamated causing this coin's surface condition as seen in the previous post/link) of this THREAD.

Another factor is in Zacatecas we have two other silver ores that would create amalgamation issues if not properly pre-treated prior to amagamation with mercury. In short - ONLY AgCL types lighter colored ores are succeptible to amalgamation and hence converted to silver EFFECTIVELY. Dark ores needed to be roasted with salt or copper sulfate. A standard pathway in New Spain Mercury Amalgamation. Here are tow other silver Koreas inherent in Zacatecas which would create amalgamation issues - these silver Koreas containing antimony (Sb) and arsenic (As).

Another sulphur containing hypogene silver mineral of commercial importance is pyrargyrite, Ag3SbS3, a sulphide containing both silver and antimony. Pyrargyrite is an important silver mineral in the mines of Zacatecas, Guanajuato and Pachuca of New Spain. Emmons, The Enrichment of Ore Deposits 625 276. 'The name comes from Greek, fire and silver ...dark ruby silver, is more common than
proustite [see below] and is an important ore of silver; a deeper red than proustite and less sensitive to light; inmining lore, high grade pyrargyrite ore is known as "blood mining" in reference to the color and texture of afreshly excavated face'. The presence of compound silver sulphide salts together with other metals would lead them to be branded as rebellious, since they did not respond in a straightforward manner to amalgamation or smelting. Another sulphide hypogene silver mineral is proustite, Ag3AsS3, which contains both silver and arsenic.
'Known as ruby silvers due to their translucent red colour when fresh, lighter than pyrargyrite. perhaps the most vivid color in all the mineral kingdom is the scarlet-vermilion of proustite ... [though] exposure to light darkens it'. Wallace, Barton, and Wilson, "Silver-Bearing Minerals," 29.83 Humboldt identifies by name silver sulphides, horn silver (silver chloride) and antimony/arsenic compounds of
silver among the main silver ores of Mexico, in Humboldt, Essai politique, Tome III, 354-61.; by mid nineteenthcentury silver chloride is identified as one of the main components in pacos or colorados, together with descriptions of silver and antimony sulphides, among others in Edward Pique, A Practical Treatise on the
Chemistry of Gold, Silver, Quicksilver and Lead, Tracing the Crude Ores from the Mines Through the VariousMechanical and Metallurgic Elaborations, Until the Pure Metal is Obtained (San Francisco: Towne & Bacon,printers, 1860), 81-84.; by the turn of the century Emmons was publishing his research on the chemistry of silver
ore deposits.

To be continued ...
Edited by colonialjohn
08/30/2019 3:48 pm
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 Posted 08/30/2019  4:32 pm  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply
Just a thought ...

If you had access to statistically meaningful populations of the 1821 Zacatecas coins, and a different year/mint for which this problem does not exist, couldn't you use nondestructive XRF and statistics?
Detection of sulfur in metals in the hundreds of ppm range is possible with XRF, according to this paper https://www.sciencedirect.com/scien...363911000262. I assume Hg can be detected more easily.
With large enough populations (20 coins of each?) I would think that statistical analysis would have a shot at supporting your hypothesis without needing access to SEM/EDX. Yes, it's indirect compared to cutting open a coin and doing the compositional profiling.

Of course, maybe access to XRF (or that many coins) is just as problematic.
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 Posted 08/30/2019  6:56 pm  Show Profile   Check colonialjohn's eBay Listings Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
I have access to XRF. But we have these two possible outcomes with XRF. A high sulfur reading on the surface could posibly be explained as environmental contamination. Just for argument sake - a sulfur level >1% is recorded and is significant but the result would be circumstantial - you can argue just with Cl its from circulation contamination. Almost all coins greater than say 100 years old almost always have levels of Cl and S on the surface. If the coin was cut in half and high sulfur or discoloration was seen in the core this may be beneficial and obviously SIGNIFICANT. But SEM/EDS would supply the actual compounds. Mercury can be detected as part of a mercury amalgam INERT compound if not annealed off from the silver cake operation - most 8Rs have trace mercury is just a question of how much in ppm is the level of Hg via XRF. XRF analysis is avaialble to me but waiting and looking for an SEM/EDS opportunity. Not sure I would cut the coin in half just for XRF and the place I bring it to probably does not have the capability to cut the piece. What is important in this post is that any week look on EBAY and tell me how many 1821 Zs 8R's in AU and above have this type of discoloration on the surface along with salt build-up in the deep crevices of the legend devices under magnification. This is NOT - Cleaning, Environmental Damage, Poor Annealing or an Improper Alloy event - IMO. JPL
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 Posted 09/13/2019  2:24 pm  Show Profile   Check colonialjohn's eBay Listings Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
I will be proceeding with just a surface SEM/EDS of this coin. The cost is $150. To cut the coin and do a core to surface scan is $500 at a rate of ~$150/hr.. Rather than destroy IMO a Mint State specimen and not knowing how over a period of time from 1821 to present how sulfur or chlorides will react and possibly make their way to the surface such as silver surface enrichment effects we will see what kind of compounds are detected in these white and dark areas, the silver areas of the coin and the crystalline growth? seen in some of the devices when viewed under a loop or stereo microscope which I believe are part of the surface of the coin - although I did not discuss this fact before in this thread in any detail. We will also search for any mercury amalgams (i.e., mercuous chloride types) which are also part of the Patio amagamation process as an intermediate by-product from ore to silver prior to heating of the silver cakes to release/recover mercury. We of course will also report Au, Pb, Sb, Fe or Cu compounds detected. See what happens ... if significant will write as an article to MNA in their Journal. We do see for example many 8R's considered IMPROPERLY CLEANED with these darkish/whitish banded surfaces. It should also be remembered that SEM/EDS will report these compounds in a quantitative manner. Normally from my experience even a well work BLACK 8R may have sulfur levels in the low singular digits and chlorides even lower - generally (i.e., <1%). If these come back higher say >5% IMO there is something else going on here other than "normal" environmental contamination from airborne sulfur or chlorides on the surface of this coin. Again the coin by the way has few hairlines on the obverse and even less on the reverse. Again when a TPG sees a non-homogenous surface he IMMEDIATELY thinks ... CLEANED.
Edited by colonialjohn
09/13/2019 4:59 pm
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 Posted 10/03/2019  8:52 pm  Show Profile   Check colonialjohn's eBay Listings Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
Coin being currently analyzed this week. Will submit findings to the Roger Siboni Beach Symposium members and its YEARLY book (C4 Members) as well as the MNA Journal.
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 Posted 10/08/2019  09:12 am  Show Profile   Check colonialjohn's eBay Listings Bookmark this reply Add colonialjohn to your friends list Get a Link to this Reply
The results by the lab came in and the paper will be published in an upcoming MNA Journal and the Siboni Symposium Book. The later is a publication from the gathering of C4 member collectors annually on new discoveries and acquisitions. I rather not reveal the exact findings here but suffice to say the TPG coin's assessment was in total error.

John Lorenzo United States
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