Mexico 8 Reales 1838 Zs Overweight - 27.6g

The coin is honest visually, Bob's specific gravity test provides a density reading HIGHER than we would expect for ~90% silver (which MAY in fact hint at there indeed being some gold in the alloy), and we have seen that in many instances, a surface-level XRF zap (especially from a lower-end device) is not perfectly reflective of what's going on with the coin's alloy in its entirety.

English full-silver fakes made for the Philippines ca. 1900? Really? I don't know it for a fact, but certainly makes sense that the Philippines (with their long-standing trade ties to Mexico dating back to the galleon trade in colonial times) COULD still have used some Cap & Rays even as late as ca. 1900... so that COULD have been a plausible target.

However, we KNOW the Chinese certainly DID imported/used Cap & Rays into the late 1800s (including many later-dated pieces). Have you encountered any legitimate evidence that the same groups making illicit bullion forgeries of the Portrait colonial pieces for China trade did the same for Cap & Rays?

Thanks for keeping us up to date. This is one of the most interesting threads I've seen in some time.




Maybe the overlapping denticles around 6:00 on the reverse?

Also, wouldn't 1860s-80s dated Cap & Rays be much more likely targets for the Boston people, etc., given that many more of those dates are observed coming from Asian hoards, bearing chopmarks, etc. than 1820s-40s dates?

realeswatcher You are correct that the weight of coins from Zacatecas in the 1830's were all over the place. Also the planchets were poor and each die was basically unique. That is precisely why they would be a perfect target for someone making silver forgeries in the 1890s to be sold in the Philippines or China. Newer 8Rs were closer to being standardized and variations were not as common. Most successful counterfeits blend in and go unnoticed.

Regarding the mix of silver with a gold trace - uniformity was established during the process of refinement. By the time the silver was coined it had been melted (along with the gold component) at least 3 or 4 times. So I can not agree that there is any possibility of a gold trace concentrating in any one spot. Copper on the other hand is driven off by refining nearly completely and is added into the silver only when it is prepared at the mint for rolling. It is melted only twice so the mix might be slightly less homogeneous.

Spots on gold (alloy defects) are far more likely because of the method used to part silver traces from gold. The two processes of parting are entirely different and that is the reason why removing the fine trace of gold from silver was not economical until electricity and chlorine treatments during refining were introduced late in the 1800s.

I also agree that more tests of Cap and Ray 8Rs are needed before contamination limits can be completely accepted. So what I need is a new lab that is inexpensive to fit my budget. I own dozens of genuine Zs coins from the time period and would love to test my entire collection of 8Rs which is near 6,000 coins (Cft and Genuine). By the way, I have tested genuine coins as well as counterfeit since 1993 and even back them every genuine Mexican 8R contained detectable gold. In all I have tested about three dozen genuine early Cap and Ray 8rs in addition to the several hundred tests run on counterfeits.

So while I absolutely agree that science is always open to test and verification, silver refined in Mexico is silver refined in Mexico. Coin, plate or mug silver is silver the distinction you draw between coins and other objects is not scientific. If the museums use the lack of gold as absolute proof forgery - and have done so for over 40 years (BTW they also charge thousands of dollars for their tests) - who are you or I to suggest we ignore this test call the coin genuine on the basis of pure assumption or wait for more information.

Like I said I am not about to take on these labs they have a reputation to protect and they have deep pockets. It is like fighting the TPG's. You are entitled to believe whatever you want but the science is against you until you document scientific tests that contradict what we now know.

hjian The lab I have used in the past does government contract work for the US space program and is currently off limits to private citizens like myself. They are also under COVID protocols. I live in North Carolina and we have a governor from the Democratic party. The lab is in a Blue county and restrictions there are far worse than where I live.

Best I can do right now is a high tech junk yard that has a good handheld XRF. This COVID is a pain in the neck.

The level of 100 PPM is only 0.01% gold (one part in 10,000) which is lower than any 8R I have tested from Guanajuato minted in the 1830s. The 6 or 8 coins I have tested in the lab from that time period were all above 1/2 percent (5,000 ppm) and the highest was around 6% gold. (That is a gold level of 60,000 PPM). I have a book (that I just finished reading this week) which contains the best summary of the data available on the refining methods used in each of the mining areas (Caja). It is a great book that is worth reading. The title is Silver by Fire, Silver by Mercury" by Saul Guerrero and it was published in 2017. It indicates that by the 1770s Guanajuato was using mercury amalgamation (patio process) for 70 - 95% of the silver produced. Smelting while possible in Guanajuato was not employed because of the nature of the silver ore being mined in the 1800s and the fact that the costs of the patio process were lower yielding a greater profit for the mine owners and mint operators (Manning and Marshall).

The English owners of the mine apparently put little effort into recovering any gold by parting so the figure of 0.0001 gold is extremely low.

At present, the new data in Guerrero's book appears to provide a rationale for raising the trace level of gold at Guanajuato far above the average of 400 PPM that applies to the Mexican Haciendas (refineries) based on country wide results. His data is far more complete for some dates than for others, however, I believe that readings above 1000 ppm will become the new standard for Guanajuato silver before 1842.

Guerrero did indicate a very shocking fact regarding the archives of many of the Mexican Cajas. It seems that a few decades ago most of the old historical records that gave specific monthly data on silver production and methods used in refining by Hacienda were sold for recycling as scrap paper. Hundreds of years of data documenting the production amounts and costs of each refinery were destroyed to make a few pesos.

hjian The 1000 ppm gold is right in the ball park for what I expect from a Zacatecas issue of 1832. So as I noted the 1832 Zs coin is likely genuine.

But this line of questions did bring to light that tweaking the use of XRF data will require ongoing research into the history of refining. Over time the picture will improve and more detailed trace contaminants will be available for authenticators.

The book by Guerrero that I referenced above covers refining methods used at various times and places in Mexico. It also seeks to correct the prevailing beliefs that after the patio process was introduced that all refining in Mexico used amalgamation not smelting.

Most historical treatments of refining in Mexico tend to be simplified statements that are convenient and easy to understand but not always 100% true. As they say the Devil is in the details. Smelting according to Guerrero was still used when certain types of ore was encountered based on the needs of the chemistry of refining.

To understand what that means to this specific case, it is necessary to look at the chemistry involved in refining. For smelting (heating the ore in a blast furnace until the rock melts) to be successful the ore must contain lead. It can be found native in the ore or the lead must be added to the ore. In Europe nearly all silver ores contain lead naturally. So in Europe smelting was used exclusively and it was successful to extract silver from ores found there.

In the America's, the discovery of silver ore in surface deposits was at first refined using smelting just as in Europe. The refiners knew from experience that lead had to be added if it was not found in the ores. So smelting was initially successful but as time progressed yields of silver fell and mines were abandoned as unprofitable. The problem was that the silver near the surface was in the form of silver chlorides (the same as mined in Europe) but as the mines dug deeper the silver changed chemically to silver sulfides (similar to the black sand that was initially discarded in the Comstock lode as worthless).

The silver found in the America's comes from geologically young quartz veins associated with the subduction of the pacific plate. These veins are only 10's of millions of years old, while the European silver ores are from rocks 100s of millions of years old. The American silver was in the form of complex sulfides which over time weathered and was chemically changed to silver chlorides but only within the "weathering" zone where surrounding rocks were porous and both water and oxygen could enter over time. The lack of slow chemical alteration of the ore was what needed to be overcome and it took luck and a lot of trial and error.

The end result was a process that was actually derived from middle ages alchemists of Italy and which was brought to the new world by the Spanish priests (who could read) and was first used successfully in Peru. This process which used Mercury to extract gold, silver and copper using amalgamation developed into what we know as the patio process.

Once discovered the patio process led to the massive outputs of silver from the "stubborn ores" that had caused the early mines to be abandoned. The new refiners could get the silver out of the tailings left by the smelters as well as from new ore dug from the ground. It lead to a second bonanza particularly in Mexico.

Guerrero's contention is that the Patio process while dominant did not work on all new silver deposits. Some silver was still smelted, but only deposits that were very high in silver content (over 1%) or had lead available. The tailings generated by this initial smelting were then reprocessed with the patio process to retrieve the remaining silver trace down to 0.01% silver.

So Guerrero's theory potentially could mean that some mines at some specific times could have lead remaining in the silver. So lead becomes a tracer of smelting as well as of European (UK origin). To tell the difference you would need to know the specific date and mint - to estimate the probability of a lead level. Mints received raw silver bars from numerous Haciendas in their Caja.

This means that it is possible that some Mexican refined silver could have lead but without the production records that were destroyed it is impossible to know exactly when or how much. The most detailed records still in existence come from the Regla operation in the Zacatecas district but those records are later in time and indicate that new mines opened after the 1860s contained significant lead bearing ores that could be smelted. During this detailed period, 20-40% of recovered silver came from smelting. So lead should still remain during that period. However in the 1830's lead is not encountered in the products of the Zs mint leading to the conclusion that lead bearing ores were not being mined in that time frame.

Not all data is lost. Annual reports provide annual totals of patio versus smelting and yield an average of 71% for patio derivation of all Mexican mines. San Luis Potosi also is noted for the highest percentage of smelting about 50-50 in peak years. So lead is more likely seen in Potosi (Mexico) silver than in Guanajuato silver over time.

The complexity of the topic is one reason why most labs and researchers keep the details of XRF results to them selves. Since Guerrero has effectively published the keys to the variation (in a few cases), I believe it is perfectly acceptable to pass along my conclusions as to the usefulness of that data.

So can modern Numismatic Forgers use this detail to improve their copies? Perhaps. I conclude that while it is possible at some levels it remains impractical from a cost perspective for a forger to do so today. I also believe Guerrero's work proves that melting a common Zs 1832 8R to make an 1832 Pi or Ca coin will never work. The only coin that could be melted to match an 1832 Zs coin is likely another 1832 Zs coin.

In addition creating a new alloy to match an XRF analysis is difficult because pure elements (99.999% or better) would be needed to fool a 10ppm Lab level XRF. Buying common elements at that level of purity is almost impossible due to cost. Simply stated - creating the perfect alloy today would cost more than it could ever bring struck as a numismatic item.

Hjian That new information answers many of the questions I have had about the lead trace found in some Mexican coins. So it is possible to have some coins of one date and mint that contain lead while others do not. The numbers of each should be roughly proportionate to the relative amounts of silver refined by patio versus smelting in the same year.