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Elements

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Elements last won the day on June 8 2018

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About Elements

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  1. This was the thread I was referring to earlier. Similar chemistry but solid state silver polish isn’t kind to coins! https://oureverydaylife.com/silver-polish-ingredients-12337531.html
  2. The nitric wasn’t hot but was conc. I then tried conc HCl. After both I looked but didn’t take photos to post but i could see lots of spots still, although some had been removed. Maybe longer may have completely removed them. If I find another test coin I can try again
  3. I want to know why nitric on its own didn’t work. It did some, but not as good as the reduction. Could simply be a case of not left long enough
  4. No acetone won’t do anything to the spots. Pretty good at removing fingerprints though. I’d also like to know what they do
  5. see these academic papers. XPS is a great analytical instrument but prohibitively expensive bit of kit It and other techniques likely point to silver sulfide, but can’t rule out copper oxide. https://www.zlate-cihly.cz/Red_dot_on_coins_surface.pdf https://www.researchgate.net/profile/Saulius_Kaciulis/publication/234224608_Gold_corrosion_red_stains_on_a_gold_Austrian_Ducat/links/0deec52deb060ed2a1000000/Gold-corrosion-red-stains-on-a-gold-Austrian-Ducat.pdf?origin=publication_detail https://www.sciencedirect.com/science/article/abs/pii/S0168583X12007987 https://www.sciencedirect.com/science/article/pii/S1001052107600308 The chemistry is similar to that well known for removing tarnish from silver coins, since the tarnish is likely Ag2S in both cases looking at the above research papers (even if it’s copper the same process works) a similar treatment should and did work. To find out why the chemistry behind the silver tarnish removal (and similar process here) I point you to redox potentials of the reactions: Cu2O(s)+H2O+2e- <—> 2Cu(s)+OH- -0.36 Al3+ + 3e- <—> Al(s) -1.662 Ag2S(s) + 2e- <—> 2Ag(s)+ S2-(aq) -0.69 The more negative the potential the more the equilibrium lies to the left. Since Al can easily donate electrons to either silver sulfide or copper oxide it can reduce either. Another forum member did this recently on his libertad and worked, the above is the reason why. @Serendipity
  6. Yes I considered this. I ended up reducing the Ag or Cu whatever it was. That would take it back to as struck. But then the reduced reactive elements I stripped away. Otherwise the spots would almost certainly come back I think. As I noted at the start I wouldn't do this on any numismatic coin!
  7. After: Not perfect but almost all spots removed. With more time maybe I could completely remove them
  8. @tallthinkev @kimchi @richatthecroft @JunkBond @Pete @sovereignsteve I tagged a few who’d shown interest in this topic in this and other similar threads. Thanks to tallthinkev for providing the perfect nasty proof for this experiment! It had everything, fingerprint, spots and scratches!! Brilliant! The fingerprints were easy but the spots were more of a challenge. I’ll discuss more later but it wasn’t as easy as imagined. I though dunk in nitric or hydrochloric...job done. But that only removed a portion. I had to try something else. Even now it isn’t perfect, something remains on the knee and by the 1 of the 1979 date." Before: