MathieuMa I only just saw your comment about the Potosi scandal which seems to infer that my statement as follows was not correct.
I still believe the statement is 100% correct - provided you understand what I am saying in historic and scientific context.
In the case of milled coinage made AFTER the establishment of the US mint's testing program for foreign silver coins (before 1803 but when I can not recall) there are NO debased coins equivalent to the Potosi cob scandal recorded.
I think that too many people and especially dealers use the well known early cases of the debasement of cobs coins to "justify" incorrectly the acceptance of counterfeit coins as actually being genuine just short on silver by 10-15%. That is an unsubstantiated assumption.
To justify these conclusions there are two facts you need to understand.
(1) The actual mint records about destructive assay tests run on newly issued foreign silver coins indicate THERE ARE NO CASES of actual debasement of Spanish Colonial coins reported where the coins were more than 3-4 % under assay. There is a 7 % debased Republican issue but Royalist colonial issues (milled varieties and the Royalist emergency cast issues) debased to that level greater than 3-4% do not exist. The US mint did notice the "secret" debasement of Charles IV dollars from 903 to 896 fine (0.7%)- so I am not being presumptive in saying that I see no possibility that any of the colonial Spanish mints could have issued a substantial number of sub-standard silver coins without the deviation being detected and reported by the mint. A few random copies perhaps but significant numbers no.
(2) Specific gravity testing has physical limits based on scale accuracy which does not allow for testing of alloys to the third decimal place of fineness except under laboratory conditions. SG is however very adequate to determine to two decimal places the actual alloy. The debased coins I was referring to were those that ARE detected by typical SG tests like we have discussed many times. In those cases the deviation (5%) exceeds the maximum deviation actually reported for genuine mint issues.
So any coin that fails a standard SG test has a minimum deviation of 50 or more points of fineness which exceeds the 30-40 point error discovered in a few cases.
That is why in the cases where SG can not provide an adequate answer - that a test like XRF is necessary.
Quote:
I really think that one of the first tests that should be done on every coin is Specific Gravity. It is a simple high school level test that can be done by anyone. A dollar sized coin is the perfect size. Riddell even suggests a simple method of making an apparatus.
Combined with a ring test - that is all you need to identify a debased coin. And in my opinion ALL debased coins are actually COUNTERFEIT.
I really think that one of the first tests that should be done on every coin is Specific Gravity. It is a simple high school level test that can be done by anyone. A dollar sized coin is the perfect size. Riddell even suggests a simple method of making an apparatus.
Combined with a ring test - that is all you need to identify a debased coin. And in my opinion ALL debased coins are actually COUNTERFEIT.
I still believe the statement is 100% correct - provided you understand what I am saying in historic and scientific context.
In the case of milled coinage made AFTER the establishment of the US mint's testing program for foreign silver coins (before 1803 but when I can not recall) there are NO debased coins equivalent to the Potosi cob scandal recorded.
I think that too many people and especially dealers use the well known early cases of the debasement of cobs coins to "justify" incorrectly the acceptance of counterfeit coins as actually being genuine just short on silver by 10-15%. That is an unsubstantiated assumption.
To justify these conclusions there are two facts you need to understand.
(1) The actual mint records about destructive assay tests run on newly issued foreign silver coins indicate THERE ARE NO CASES of actual debasement of Spanish Colonial coins reported where the coins were more than 3-4 % under assay. There is a 7 % debased Republican issue but Royalist colonial issues (milled varieties and the Royalist emergency cast issues) debased to that level greater than 3-4% do not exist. The US mint did notice the "secret" debasement of Charles IV dollars from 903 to 896 fine (0.7%)- so I am not being presumptive in saying that I see no possibility that any of the colonial Spanish mints could have issued a substantial number of sub-standard silver coins without the deviation being detected and reported by the mint. A few random copies perhaps but significant numbers no.
(2) Specific gravity testing has physical limits based on scale accuracy which does not allow for testing of alloys to the third decimal place of fineness except under laboratory conditions. SG is however very adequate to determine to two decimal places the actual alloy. The debased coins I was referring to were those that ARE detected by typical SG tests like we have discussed many times. In those cases the deviation (5%) exceeds the maximum deviation actually reported for genuine mint issues.
So any coin that fails a standard SG test has a minimum deviation of 50 or more points of fineness which exceeds the 30-40 point error discovered in a few cases.
That is why in the cases where SG can not provide an adequate answer - that a test like XRF is necessary.

















