dosmundos You ask:
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The Ponterio and the NGC coin appear to be Sheffield plates. What are the counterfeits you own and/or have seen? Riddell describes his coin with a fineness of "near 63-1000". Would this mean that he melted the coin, thus mixing silver plating and copper core, and received the 6.3% silver content, without describing the coin as being copper with silver plating or silver wash, something he does with many other examples?
The two coins are in my opinion BOTH Sheffield plate examples.
Your question has several parts.
My experience with the Riddell # 221 and 223 indicate that most examples are thin Sheffield plates. But the composition does range from solid debased alloys (with and without thin washes) to thinly plated copper cores. One of the scarcest types is a solid copper strike. A thin Sheffield Plate would square very well with the assay results of 6.3% silver. I have NEVER seen an electroplate (with the exception of one example where a later electroplate was added OVER the earlier Sheffield to cover worn through spots.)
The assays found in Riddell did consist of melting the entire coin. His primary concern was the approximate value of each of the counterfeit coins based on silver content. (It is my belief that Riddell wanted to create a listing of counterfeits for redemption purposes.) He was not concerned with the preservation of his exemplars. He even melted the # 182 a genuine 1835 Ho coin which is still unknown in any collection to date. (A very similar coin has recently been discovered and is also considered unique).
I base the theory that Riddell's goal was to create a handbook for redemption of forgeries on the fact that several Riddell examples produced from identical dies were assigned more than one number. The only difference is that they had different assays. Numbering the coins according to assay appears to be the primary importance he saw in his work. That may account for why he never issued volume 2 as he originally planned since he should have discovered very quickly that the counterfeiters used different assays at different times indiscriminately. He could not rely on die variety as a measure of actual value.
You also ask why he didn't mention it was clad coin like he did in other cases? Good point. I can see more than one reason for that. First, he may have had an intact Sheffield to begin with for testing. It makes sense to melt the least circulated copy for assay purposes if redemption value is your goal. He also indicated that these copies had flooded the local (New Orleans) area so high grade copies were quite likely.
But there is a second equally plausible reason. He simply did not mention the fact. After reading through his book and creating a spread sheet of all the data presented for each example - one simple fact became apparent to me - Riddell was not always consistent in his terminology and his descriptions. Most of his descriptions do not contain the answers to all the parameters he mentions. Some descriptions for example may say cast or struck - but many say nothing about how the coin was made. Some refer to solid alloys, some to plates and others to silver washes but many say nothing about the coin's composition. Riddell often neglected to mention individual facts in MOST cases. When you look at a completed spreadsheet of the entire book the failure to provide precisely the same data for each coin is obvious because of the number of BLANK fields in the end product.
So missing data in Riddell does not bother me.
Now that I have completed a book with over 500 descriptions - I can vouch for the exceptional tediousness of producing such a list and trying to mention every parameter in every single description using the same terms and getting them in the same order. It is BORING to prepare such a listing.
Your second question is:
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XRF does not help with (intact) Sheffield plates. But due to its copper core, a Sheffield plate should be underweight, and should not pass the SG test, right? So would that be the way to test the NGC coin without cutting it?
The answer is YES regarding Specific Gravity. It is a non-destructive test that can determine if a coin is a forgery WITHOUT cutting the surface in any way. That is why I began using SG testing to confirm forgery in the first place. I began my collection of counterfeit coins while I was in High School about 1962. About that same time, in the school science and chemistry laboratory I learned the story about Archimedes and his method for testing the King's new crown. If Archimedes could prove whether or not the crown was solid gold in 200 BC shouldn't I be able to tell if a coin is solid silver or not NOW? So yes - a clad counterfeit coin like the Riddell 221 will be the wrong density even though it may be exactly the right weight. It was obvious to me when I was 15 years old that density not weight was the determining factor.
The third question is:
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Are there any visual hints for a Sheffield plate you would be looking for if you took the NGC coin out of its plastic coffin? Or is there no way of telling as long as the plating is not damaged or worn through?
Once again the answer is yes but with qualifications. First, if the coin remains in the holder you look for several things that may have happened which are still visible. One is the trace of an edging ribbon. A Sheffield coin was cut out of a strip of metal that had three layers. The top and bottom were thin silver and the core off metal. So when a blank was cut - the edge was exposed and had to be covered in some manner. Some of the methods do leave traces. The most common method after about 1785 was the ribbon method in which a thin silver ribbon was rolled onto the edge and folded over slightly onto both faces. This was usually done as the blank was edged before the coin was struck. The final strike of the faces welded down the edges of the ribbon that overlapped. Here is what that looks like on a near MS example of a 1791 Sheffield plate counterfeit from Birmingham, England.
This very visible seam is only observed on coins with virtually no wear. But there has to be a seam. As time past the forgers got better at placing the seam RIGHT AT THE CORNER of the coin.
There are other signs. The principle used in the Sheffield process was that silver and copper have the same properties of malleability. When three silver layers are welded together (usually by heat) they can then be rolled and drawn and the three layers will expand at the same ratios. That is why it took many years of experimenting with alloys to produce a white core that would be satisfactory as a Sheffield layer. If the three layers do not deform at identical rates one layer thins or cracks.
I believe this effect (indicating a poorly matched metal sandwich) occurs on the Ponterio copy. Note the areas on the outer flow side of high struck features. The silver plate seems to thin and the effects of oxidation cause a subtle change in toning. See below:
So yes, it may be possible to find clues while still encapsulated.
Removal would provide the ability to test the coin using SG. That would prove what the coin is. There is NO
TPG that offers SG testing on a routine basis - yet it takes only a minute or two per coin to complete.
I do not suggest removal at all. I think that part of the value of this example is the ERROR of encapsulating the coin in the first place.
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Posted 01/31/2014 05:33 am
