Gold As A Marker For Early Silver Coins

Won't counterfeiters just start adding 0.2 percent gold to their early silver fake coins from now on?

thq - Interesting article - VERY INTERESTING INDEED. It actually adds some new data that will aid in authentication of certain types of coins. Thank you for uncovering it.

I hope more similar articles can be discovered by you and other members. I need more eyes and much more time to process the data that is out there. This is not a one man project.

I will start by saying that after reading the paper a few times, I believe that gold MUST be found in the 8 reales made from 1770 to 1820 in Mexico City and that the level of gold was clearly underestimated in my earlier notes and writings. Whether 2000 ppm is correct or 1000 ppm or some other range I do not know yet. I also want to re-state as fact that the 12 ppm gold reading I got for my own 1805 Class 2 coin (secured from a forger who made the coin in 1920) is vindicated by these two reports and that the existence of Class 2 coins from Mexico City is also proven. That coin was NOT made in 1805 and does not have an 1805 Mexican signature for metallic content. The coin is simply NOT GENUINE regardless of any opinions to the contrary based on appearance, gut feelings or expertise. The following coin is a Class 2 Silver counterfeit made ca. 1920 in New Bedford, Mass.



Regarding this new report it appears to prove several of my contentions. First that silver was a contaminant in all gold mined in all locations of central and most of south America and also that gold was a contaminant found in silver at all the same points as well. Gold coins and ingots shown in Table 1 of the above report indicate that refining and especially parting of silver from gold (a different process than parting gold from silver) was not a very precise process anywhere in colonial Spain. The yield ranges are actually far lower than the theoretical capability of the methods known to be employed. I ascribe that to poor working conditions, haste to produce as much cash for the crown as fast as possible and probably to use of slave and semi-slave labor. The range of contamination is 0.8% silver to 25.4% silver in finished gold coin and ingots. The mean of the 56 readings is 12.74% silver contamination. However the single reading of 25.4% silver contained in the final Mexican entry dated 1818 can be labelled as aberrant (possibly a counterfeit but certainly a fraudulent coin.) Removal of this one item results in a mean of 8.0% contamination. Average contamination using the 55 tests (excluding the aberrant Mexican reading) yields an average of 6.32 percent.

Calculated by country of origin, the averages are:

Brazil 10 tests 6.77% silver
Peru 7 tests 7.03%
Mexico 7 tests 7.13%
Columbia 12 tests 10.03%
Chile 4 tests 9.30%
Bolivia 1 test 7.40%
Ingots 15 tests 6.05%

This indicates to me that the capability of parting silver from gold was NOT done using nitric acid or if acid was used it was not repeated multiple times as it should have been. It appears that cupellation and roasting was a very poor method of producing pure gold or silver at this point in time.

It is dismaying that Table 3 which lists 25 gold coins (typically later dates than Table 1) does not include the trace contamination of silver at all. The point of the table for the authors of the study was clearly to demonstrate the correlation of other trace contaminants with specific areas or mining regions. Omission of silver levels may have been intentional to maintain some level of secrecy.

I have found that it is difficult if not impossible to gain access to any of the trace contaminant data bases created by any of the testing labs. They maintain their data and hold it close to the vest.

Regarding Table 4 - This table refers to silver coins and shows gold as well as other metals as contaminants. The lowest contamination of gold in silver comes from the products of the Potosi mint and in general from mines in the earliest periods of production. This period is unique because the highest levels of native gold and silver were being removed from the mines (the choice ores) and silver taken from the indigenous peoples was included in the numbers. These early silver and gold deposits were refined very wastefully because the methods need to refine "stubborn" ores were not in place. More on Potosi will be discussed below.

The first grouping of coins in Table 4 are from Alphonso VI of Portugal and these show clearly that two sources of gold are represented (see report indicating Potosi and Mexico as the sources). Mexico has Au (gold) as a primary marker and Potosi has As (arsenic) as a contaminant. Where gold is low, arsenic is high and vice-versa. Portugal, it must be noted, did not employ pan amalgamation during this period. I am unsure of the parting methods employed, however, I am very sure that later post 1870 methods REMOVED Arsenic from the silver. It is therefore a simple substitution of Arsenic as the contaminant that must be present in Potosi coins NOT gold.

Likewise the Bahaia issues are Portuguese in nature and the ores came from the same sources with the addition of some native Brazilian ores. I would speculate based on the data from Table 4 that the ores were mixed closer to a 50-50 ratio than the earlier coins because both Au and As contaminants are present. The sum of the two contaminants approaches an average of 1000 ppm. It appears to me that a likely marker for authenticity is the presence of BOTH As and Au in coins from Bahaia.

The single coin from Guatemala in the study (1808) has a silver contamination of 0.087% (870 ppm). That is four times as high as my threshold number and appears to display a similarity of Guatemalan ores with Mexico, which is geologically sustainable. Remember that the North American and South American plates were not from the same area of the planet at the time of the gold/silver intrusions into the igneous rock that formed the mountains. Here we are entering the field of plate tectonics but the basic facts fit. The Andes and Sierra uplifts and intrusions occurred at different times and at substantially different locations.

After Guatemala, Potosi is addressed in Table 4. The first 6 coins of the 14 tested have the lowest concentration of gold as a contaminant of any of the coins on the table. It must be noted that these six coins were NOT made with silver extracted by mercury amalgamation. That process was developed in Mexico in 1557 and took a few years to spread to Potosi (1570 to 1572 are best estimates). So it would appear that pre-amalgamation coins have a different profile of contaminants that must be present. Mercury amalgamation unlike cupellation carries Arsenic unaffected into the metal pool extracted from the ore. Arsenic is a white metal that amalgamates with mercury just like silver and gold. If there is no reduction step in the process (which appears to be the case) then Potosi gold should be contaminated with Arsenic - and it is. Fortunately these coins are fewer in number comparatively and they would not be likely to skew the results of tests done on later date European coins that were tested. Remember that Mexican silver production predominated by 1770 which is the start of the interval studied in my book. It is a fact that Mexico was producing 5 times as much silver as Potosi in 1770 (see Figure 2.) and that this disparity increased with time. By the early to mid-nineteenth century estimates indicate that over half of all the silver in the world originated in Mexico. That is enough to contaminate virtually every silver coin produced after 1800 and before 1850 with traces found in Mexican silver. So unless the silver was parted before being re-coined the contaminants present in Mexican coins should also appear in coins made from them. The ability to part to a threshold below several hundred ppm was not available anywhere before 1850.

Lima coins show a 203 ppm average gold contamination and it appears that most if not all were pan amalgamation silver. I question the first coin because of the 15 ppm gold trace combined with 2075 ppm arsenic. This looks like potentially a coin from a different source or one refined with a different process. Regardless of the 15 ppm gold reading, the 2075 ppm arsenic level (OVER 2% arsenic) is an indicator of appropriate age but perhaps not authenticity.

Finally we get to Mexico and the 15 coins that were tested. Of the 15 coins, 13 are from the period before or immediately following the adoption of amalgamation. These 13 coins average 1,679 ppm gold. This is the highest of all the countries tested and clearly indicates that gold is the primary contaminant in the ore. There is one reading of 160 ppm that I would be concerned was an aberration because it occurs along with a low lead level. However, in this table lead was not always determined. The tests for our book would point to this lead content as being simply too low to be genuine.
If you eliminate issues of Mexico struck before the patio process was developed - you end up with just two coins. The coin from 1758 had a gold contamination of 560 ppm and the coin from 1821 had a gold contamination level of 2155 ppm or 2.12% silver. In producing our book we tested over 200 coins from the 1770 to 1821 period not just two. Our average result was much higher than 200 ppm. Unfortunately I lowered the number because of the Potosi results. It is time for me to look back at these data to see if Arsenic was present in a higher ratio and to eliminate gold as a criterion for Potosi ONLY and instead substitute Arsenic as the primary contaminant.

Based on both reports you also need to take into account that the newest test series expand the number of trace contaminants in silver and gold to include As, Zn, Cd, Sn, Sb, Au, Pb and Bi. These elements when trace levels are determined form a pattern that in combination clearly suggests whether a particular coin was made before 1850 or after 1850. The specific data in the 1999 report that I first cited used normative data not actual data. The authors of that study indicate."For security reasons, only relative values are shown." I do not necessarily agree with that position but I accept it.

I am not suggesting a FIXED number at this time - but it is very clear that Mexican coins using silver extracted by the patio process followed by cupellation and roasting could not remove all of the gold from the silver. The levels fluctuate but they are normally well above the 200 ppm level I used and at times even EXCEED 2000 ppm. Most hand held XRF guns have an accuracy level of 0.1% or 1000 ppm so a small technological advance might remedy this concern.

I am still looking for other peer reviewed reports and tests on this subject. The report discovered by thq may have disclosed too many specific numbers but both seem to confirm not deny my basic theory.

The second question was raised by pepactonius. He says:




One factor that is good for authenticators is the "from now on" part of that statement. Only from this time forth (actually 1999) would forgers even know they had to add gold. So any coin that has a provenance dating back to 1990 would be unlikely to have a corrected alloy. This is one reason I published pictures of all the counterfeits I was aware of so that I could fix in time those coins. The simple fact is:

NO CORRECTION OF A FORGERY CAN BE MADE BEFORE THE ERROR IS KNOWN AND PUBLISHED.

Pepactonius, I used to wonder the same thing myself until I realized that gold is only one of an array of trace contaminants that belong in some coins and not in others. As long as too many results do not get leaked out the average forgers will not know which and how much of each element to add to get a correct signature. Gold is one of the easiest metals to purify to a state of 99.9999% fine; VERY FEW other metals can be economically refined to anything near that standard.

Where in the world would the average forger find 99.9999% pure Arsenic, Zinc, Cadmium, Tin, Antimony, Lead, Bismuth etc.? Even 99.99% copper is hard to find. Most copper is a real hodgepodge of trace contaminants. Many would raise red flags.

In addition, whenever an alloy is created in a furnace, the forger will face another issue. Cross contamination. It is not the large components of the alloy that will get you discovered it is the trace contaminants.

So starting at the beginning, where would you get your silver? Silver is not commercially available in a state purer than 99.99 fine. It is easy to say "I will melt old period coins" but it is increasingly expensive to buy them. I do expect that old culled coins will be recycled, but unless the forger separates his silver by mint he will screw up.

Let's say a forger was able to re-melt enough coins from only one mint and one time period. Would that insure silver that contained the correct signature? That depends on the furnace and fuel used. In our more than 200 tests, we uncovered a few modern fakes because they had odd signatures. One of the metals present which did not belong was an element added to furnace linings in the 1930's to make them last longer. At temperatures needed to melt gold there is a trace contamination from the lining to any open crucible inside. This element is common in very recent silver but it has no place in Mexican or South American silver. We also discovered that SOME rare earth elements are NEVER found in period coins but others are always there. These odd elements can make their way into silver refined after 1980 if the source used silver reclaimed from recycled computers. There are some rare earth elements like Yttrium and Scandium which belong in some of the silver. Where would you go to get them or Iridium? You can't pick them up at your local pharmacy.

So I leave you with a final comment, that even if a forger gets his hands on the correct formula: He cannot, at this time, duplicate it economically.

thq I agree 100% - the value of the arsenic trace for Bolivian silver was an entirely new and unsuspected clue - so thank you for finding that report. That clue now gives me an answer for XRF test results that had skewed our gold numbers when Bolivian tests were mixed with Mexican. It also serves as a warning that Peruvian may be slightly different as well (we tested very few Lima coins).

You bring up a very valid point which applies to not only California but New Orleans and Philadelphia as well. The US melted millions of Mexican coins to secure the silver for our own coinage. It is possible that both silver and gold coins produced may be verifiable by this trace method.

The first thing that needs to be determined are the assay and refining techniques used in the US to determine if nitric acid parting or some other parting method was used. The use of nitric acid was far more likely to occur in the US because by 1860 industrialization was well under way. I also recall something from a mint report in the early 1850s that suggested buying War time Mexican silver coins specifically to remove the gold content.

The same method I am suggesting can be used with any coinage as long as the sources of silver can be defined and the refining techniques used are known. It is a brand new field that holds great promise for authentication. Forcing the counterfeiters to get the assay correct should allow the products of all but the most sophisticated forgers to be detected.

thq There are many such reports buried in technical journals of arts and antiquities. No one has ever attempted as far as I know to systematically collect and correlate all the data except the Winterthur Analytical Laboratories in NY. I attempted a contact there with no success, so I asked my laboratory contact at the RTI labs to check into it to see if they could get access to the database.

It is very sad to report that most numismatists gave up on this technology early on for reasons that are no longer valid. I discovered this based on the comments that were contained in the summary report from ANS when they rejected my book for publication. They cited the same old out of date information that I have heard in several forums where I have spoken. The "general consensus" among numismatists is that experienced dealers can tell genuine from forgeries in a nearly "mystical way" better than scientific tests.

Very early testing was rejected by the coin industry as too costly and the theory was attacked because there was a general lack of empirical supporting data. Most of the data employed to attack XRF technology dates to the 1990s or earlier.

That has now reversed - tests number in the thousands and trace markers are accepted for authenticating all types of silver EXCEPT coins.

Why ?

Dealers fear they will be discovered as "empty suits" selling as genuine coins that can be scientifically proven to be fakes. The same goes for the TPGs. Coins are big business and money is far more important to the establishment than historic truth.

John, I think you are following in large part the line of argument used before 1999 to discredit origins tests using XRF test. This was the same line that has been adopted by the opposition including Mexican Coin Company representatives at my presentation in Arizona last year and since. It was based on the belief that variations within the trace contamination in various parts of ore deposits make mine or vein source detection impossible. That presumed fact was incorrectly applied to cast doubt on the entire process I was presenting.

One has NOTHING to do with the other. Remember, my line of argument is not that I can prove the origin of the metal down to mine or vein at all at. The three major intrusive systems - Mexico - Bolivia and Peru can and HAVE been conclusively identified by museum tests of early artifacts. They have data establishing ranges of contamination of 8 marker elements. What that has proven is that the gold marker so predominant in Mexican silver is NOT as apparent in Peru (about half) and barely present in Bolivian silver at all (about 5%).

What can be proven is the date of refining, parting and manufacture of items based on silver purity and the composite of other retained trace contaminants.

The industrial methods used to refine silver are all known from studying history. The imports of mercury and nitric acid are also documented for each country. The availability of water and wood are also well covered by numerous written sources. The success of each method was confirmed by fire assays done at the time and more recently by XRF and SEM by several different laboratories. With that data base - it is not conjecture or speculation at all that the process is a KNOWN parameter. If we know how the silver was refined - the end state purity can be established - it is simply not ore dependent it is based on the chemistry employed to refine the metal.

The ecconomical parting of trace gold was NOT a priority in most Mexican producing silver mines. I have found a source from 1827 that indicates NONE of the branch mints in Mexico even attempted to part the trace of gold from the silver. This means that higher than minimum gold levels (0.2%) should be seen in cast coins actually made during the war years not a lesser amount.

Another issue which can be proven is that the nitric acid method of parting WAS NOT used in Mexico. Fire reduction was the only method in use. This is a simple economic fact. It is impossible to part a trace of gold found in a mass of silver. The reverse is possible - removing a trace of silver from a mass of gold is when the acid method was used.

There was no place in the world that could produce 99.999 fine silver in 1799. Natural silver in crystaline form was at one time known to exist in Mexico but even thatr was not 99.999 fine. This form of silver, according to numerous sources was gone by the first decades of the 18th century in any event. The big mining efforts Real del Monte were producing silver from low grade silver sulfide ores that were refined by the patio process. Any high grade silver ores were fire refined and the residues were treated with mercury.

The book may be ahead of its time for numismatics which is basically still operating with techniques that are 100 years old.

It is frustrating to deal with people who follow personal financial gains over truth.

> It is frustrating to deal with people who follow personal financial gains over truth.
That sums it well, indeed .

Hum, just rechecked the Chihuahua 8 reales that you analyzed - Au is between 0,22 and 0,91 depending on the area (where it's at 0,22 is a brown area, rich of ~45% copper and only ~55% silver).

Reading the book on California silver was also educational for learning a little about the development of silver refining techniques. At the Comstock the early refining was done by the traditional Mexican pan amalgamation, mixing mercury/water/salt/copper sulfate with the ground ore to make a pulp, then spreading the pulp on a patio in the sun to form an amalgam. This was modified into the Washoe Process to work ore faster, using stamp mills for grinding, followed by amalgamation in 300 lb batches in an iron vessel.

Apparantly the early 1700's Mexican vaso process of roasting the ore in an oven to directly smelt silver wasn't used on the Comstock, but was practiced extensively on the Cerro Gordo ores. Because the Cerro Gordo ore contained mostly lead, which forms a flux with the silver, a modified direct smelt process based on vaso was used to process most of the ore into 80 lb lead/silver ingots. The exhaustion of the lead/silver deposit needed for roasting effectively ended all Cerro Gordo mining in 1877.