https://nnp.wustl.edu/library/book/581571Surface Enrichment in Medieval Indian Silver Coins- Shiny Deception
I found this talk very applicable to the surface enrichment phenomenon. I did not attend this talk in NYC at the NYITL and it is two years ago but I found the results noteworthy to the effects of silver surface enrichment (SSE). If we view the standard reference L. Beck on SSE:
https://www.researchgate.net/public...e_techniquesBeck made three conclusions:
1. Silver alloys with copper between 15-20% or less the SSE effect will be minimal between surface and core.
2. 15-20% >Ag< 72% its dependent on factors like annealing, environmental conditions, etc. on what the silver surface value enrichment will be as compared to the inner core.
3. Ag >72% expect elevated levels consistently.
In his talk John Deyell actually used a noted Canadian analyst which was the same analyst Mike Diamond used on my
Peace dollar lamination study for verification in a
Coin World Collector's Clearinghouse. Anyway - he knows his business ... his conclusions were correct but he was still a bit confused in the #2 aspect above. Studies have shown that sometimes the Ag here can be close and he never mentions he did any form of polishing on his surface studies. From my studies for #2 above I have seen XRF surface (polished) and XRF core to be in somewhat a close agreement. So what is my point here in this post - if I attended the meeting I would have advised the following:
1. Indeed - if the surface XRF study on a polished edge (i.e., less noticeable) is 20% or less in a Ag/Cu alloy expect the inner core to somewhat mimic the surface readings. VERY LITTLE quantitative differences.
2. For Ag in the 20-70% range this will be coin dependent and either slicing, procuring drilled core samples or just ballparking a polished edge in some situations may be adequate. Results will vary coin by coin. I think he had large differential readings as the surface results were from an UNPOLISHED surface reading.
3. If 70% or higher expect significant changes. I once did a silver surface enrichment study on a 1964 Kennedy 90% Half Dollar. Both core and surface readings were IDENTICAL! It takes at least a century or more for SSE to take effect in my opinion. On the other end of the spectrum I have seen surface readings of 99%+ on ATOCHA 8R seawater salvage pieces with all the Cu being leached out coupled with the SSE effect!!!
This is a great first talk and study on debasement of issues with time but it shows for exact quantitative readings anything above 20% may need to be sliced or for core samples to be taken. Polishing the edges may negate this but I never undertook a debasement silver/copper XRF study. John Deyell did a great job! But as he inferred it can be overwhelming at first ... <BG> John Lorenzo Numismatist United States
Posted 02/13/2022 2:48 pm
