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Author Topic:   Metal analysis
swarter
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iconnumber posted 05-19-2003 12:24 AM     Click Here to See the Profile for swarter     Edit/Delete Message   Reply w/Quote
Last November there was on this forum a topic on the nature of coin silver that generated quite a bit of discussion, including references to the metal analysis used by Winthur to determine metal composition.

X-ray flourescence was also used by the Cleveland Museum which holds many objects from the Hollis French Collectino in which there were claimed to be a considerable number of fakes and forgeries, among which were a number of supposed American objects declared to be of English origin, based on a lower percentage of impurities (more closely meeting the higher standards of purity of English Sterling).

I have been uncomfortable with some of the assumptions of forgery or misattribution published in the Cleveland Museum book, and have wondered if some of the rejections might not have been too hasty. As was mentioned, we know from contemporary sources that many Amrican objects were in fact made of old or out-of-style English Sterling brought to American smiths to be remelted and made into new objects in the "latest styles." Perhaps Fredz or another metalsmith can tell us if there was anything in the remaking process that would have introduced contaminants (assuming no other silver was added) sufficient to affect the metal composition and render it no longer equivalent to English Sterling. Or is it possible that the layer of pure silver raised to the surface during the annealing or "Pickling" process would have worn thin from use, so that less silver therefor would remain to mix back in with the now more concentrated impurities left behind in the deeper layer and thus raise the total content of imppurities in the remelted product? Or should Sterling still be Sterling after remaking?

[This message has been edited by swarter (edited 05-19-2003).]

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Scott Martin
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iconnumber posted 05-19-2003 09:11 AM     Click Here to See the Profile for Scott Martin     Edit/Delete Message   Reply w/Quote
Before comparing the the X-ray fluorescence data from these different institutions, an understanding of the actual technical approach to doing the testing is required. See WEV's 01-18-2001 thread An interesting survey and my reply:
quote:
I have had some experience with commercial X-ray fluorescence testing and have found that there are a lot of variables which can effect the results. For example:

  1. How (and/or how well) the device is calibrated.
  2. What area or areas of the object are tested.
  3. Whether only the surface is tested or a sampling of the sub-surface is tested.
  4. The condition of the object and how it was prepared (cleaned) before testing.
  5. Etc. etc. etc.


What would be interesting is for institutions which do this type of testing to share the same set of objects to test and then we might have a baseline for comparison.

I share your concerns.

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FredZ

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iconnumber posted 05-19-2003 09:14 PM     Click Here to See the Profile for FredZ     Edit/Delete Message   Reply w/Quote
I tend to agree that there is much controversy in declaring an item as a forgery just by metal content. If the smith only used the metal from an English teapot then the metal content of whatever item he made would be identical to the parent metal.

Many factors have to be taken into account when discerning fraudulent items. I am not certain how the pure silver surface that pickling creates effects the spectroscopic analysis.

I and curious how different parts of the vessel tend to show different metal analysis if it is not due to the wear of the naturally occuring depleation of the base metals during pickling.

I understand that it is possible to create an ingot that is not completely homogenous and I do not think it is a common practice that would show on this type of analysis.

Fred

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swarter
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iconnumber posted 05-19-2003 10:55 PM     Click Here to See the Profile for swarter     Edit/Delete Message   Reply w/Quote
Thanks for your answer, Fred.

Perhaps I can suggest another possibility for the lack of uniformity you mentioned in silver content in and among some American pieces, and that would be related to the unavailability of sufficient silver of a uniform standard for silver made in the Colonies or the Early Republic. Until the discovery of the Comstock Lode there was no viable domestic source of quantities of raw silver; objects were often made to order for customers who had to provide their own silver to be melted and remade. This could have been old holloware or spoons, but more often was in the form of coinage. Slversmiths also advertised for old silver to brought in for purchase. In the bigger cities, more prosperous smiths imported ready-made objects from England for resale. Others, like Paul Revere, sponsored privateers to obtain their silver illicitly on the high seas. Throughout this period quantities of foreign coinage of varying standards were in circulation and silver content of objects made by a smith could vary widely in content; lids, handles, foot rings, etc., could have been made from different batches of melt, or perhaps variation could have resulted from incomplete mixing of a batch made from mixed coins. This lack of standardization must have been recognised as a problem, because by 1827, the Wilsons (who operated a thriving business in Philadelphia manufacturing silver objects for resale to smaller retailers) could advertise (quoted by Belden) that their silver was marked according to the content of the silver from which it was made (or was equivalent to ?), in descending order: "Crowns," "5 Francs," "Spanish Dollars," and "Standard." This must have been a successful tactic, because spoons marked "STANDARD" appear in numbers with other retailers' names throughout Philadelphia and points south and west - higher quality marks are much scarcer. In Baltimore there was a relatively short lived attempt to adopt a coin standard with silver marked "10.15 oz" (with "11 oz" added later for "English Sterling"). Ultimately, when raw silver (and refining techniques) became readily available, a US coin standard was adopted, and uniformity was achieved.

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nihontochicken

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iconnumber posted 05-20-2003 12:27 AM     Click Here to See the Profile for nihontochicken     Edit/Delete Message   Reply w/Quote
Has anyone tried neutron activation analysis? This shouldn't be significantly affected by surface pickling or similar surface effects. However, due to the radioactivity involved, I'm sure there are are lot fewer places that can do this as compared to X-ray fluorescence.

Rick

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