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Posted 08/19/2017 11:45 pm
I returned to this thread because of the new posts and realized that ShadyDave had offered to sell a magnetic 1933 slabbed sol. I had missed the offer earlier. Hopefully Dave or someone who knows him will relay my interest.
Regarding my offer to post more information on why the reliability of Handheld XRF is adequate to test Mexican 8Rs for gold but for not diagnosing the actual Ag versus Cu levels in many older coins. I am still far from completing a draft of my proposed chapter on XRF because the subject is still under active research and I am concerned that a preliminary draft may not resemble the final text.
To summarize my findings so far:
1. The denser the metal the deeper beneath the surface it can be detected with XRF at a given power. That is why the shallow depth of penetration of a handheld XRF unit can accurately detect gold in and beneath a toning layer while miss reporting the lighter elements like copper and silver.
2. The thickness of toning caused by the corrosion of both silver and copper absorbs the XRF signal of the handheld unit so that a ratio of Silver to copper may not be accurate on deeply toned coins. Black toning silver sulfides are actually the worst form of toning for XRF to penetrate.
3. Older coins were made in several steps and in the case of 8Rs they were usually annealed several times prior to issue using fire to heat the blanks and planchets. The thick visible scale was removed by lengthy immersion in a warmed acid bath. This results in the depletion of surface copper when compared to silver. This same technique is used by counterfeiters to make a high copper alloy look like coin silver. That is why many of the 50% sols test 80-90% silver using the cheaper surface XRF tests (including SEM). The actual return signal depth of copper is almost identical to the thickness of the depletion layer when a coin is immersed in acid for more than a few minutes. As a result the ratio of silver to copper detected is wrong.
4. I suspect that the Peruvian and US mints both intentionally gave planchets an extra long bath in acid to enrich surface silver and improve the final color of the one and one half sol coins. The first issue of the 50% alloy was so poor in color that they did not circulate well. Later issues in high grades have great surface color far closer to 90% silver than 50%. The same effect can be seen on the Wartime 5 cent US coins in MS grades.
If you put together all of the piece parts of the Sol puzzle uncovered so far and you should see that the tests support this conclusion.
Regarding my offer to post more information on why the reliability of Handheld XRF is adequate to test Mexican 8Rs for gold but for not diagnosing the actual Ag versus Cu levels in many older coins. I am still far from completing a draft of my proposed chapter on XRF because the subject is still under active research and I am concerned that a preliminary draft may not resemble the final text.
To summarize my findings so far:
1. The denser the metal the deeper beneath the surface it can be detected with XRF at a given power. That is why the shallow depth of penetration of a handheld XRF unit can accurately detect gold in and beneath a toning layer while miss reporting the lighter elements like copper and silver.
2. The thickness of toning caused by the corrosion of both silver and copper absorbs the XRF signal of the handheld unit so that a ratio of Silver to copper may not be accurate on deeply toned coins. Black toning silver sulfides are actually the worst form of toning for XRF to penetrate.
3. Older coins were made in several steps and in the case of 8Rs they were usually annealed several times prior to issue using fire to heat the blanks and planchets. The thick visible scale was removed by lengthy immersion in a warmed acid bath. This results in the depletion of surface copper when compared to silver. This same technique is used by counterfeiters to make a high copper alloy look like coin silver. That is why many of the 50% sols test 80-90% silver using the cheaper surface XRF tests (including SEM). The actual return signal depth of copper is almost identical to the thickness of the depletion layer when a coin is immersed in acid for more than a few minutes. As a result the ratio of silver to copper detected is wrong.
4. I suspect that the Peruvian and US mints both intentionally gave planchets an extra long bath in acid to enrich surface silver and improve the final color of the one and one half sol coins. The first issue of the 50% alloy was so poor in color that they did not circulate well. Later issues in high grades have great surface color far closer to 90% silver than 50%. The same effect can be seen on the Wartime 5 cent US coins in MS grades.
If you put together all of the piece parts of the Sol puzzle uncovered so far and you should see that the tests support this conclusion.
and thanks for the vote of confidence. 
