I received this Cappadocian drachm of Nero in the mail today and, not having much of an investment in the coin, figured I'd take a stab at freeing it from its encrustation using my limited coin cleaning skills. As a starting point, I gave it a few short soaks in sodium thiosulphate to remove the horn silver (~5 mg in 30 ml hot water), picking away at it with a toothpick in between soaks. Following that, I was left with some hard red and green oxides, which were not responding to the previous method. I assumed these were iron/copper oxides. I took the coin to my jewelry workshop, where I keep a small crock pot of "pickle" (a mild acid) that I use to remove oxides from sterling silver jewelry. The pickling compound is Sparex #2, diluted in water, which is heated to speed up the oxide removal process. After a few short 3-4 minute soaks in the hot pickle, the remaining junk was easily removed with a toothpick and short bristled toothbrush. The coin still suffers from rough surfaces, a flan crack, an ugly flan, an off-center strike, and crystallization, but at least it's free of the ugly oxides and horn silver it had before. If anyone has insight into what I did right or wrong in this cleaning process, I'm all ears. This was just a fun trial for me, and I only had $60 on the line. Before cleaning: After treating with sodium thiosulphate, before soaking in mild acid: After soaking in mild acid: Cappadocia, Caesarea-Eusebia, Nero AR drachm 54-68 AD Struck RY 10 = 63-64 AD Obverse: NERO CLAVD DIVI CLAVD F CAESAR AVG GERMA; Laureate head of Nero right. Reverse: ET - I; Mount Argaios surmounted by statue of Sol-Helios, radiate, holding globe in his right hand and long scepter in his left. References: RPC I 3649; Sydenham 85; Henseler 63. 20mm; 3.4g Feel free to post before/after cleaning photos, Roman provincial coins from Cappadocia, coins of Nero, or anything else you think is relevant. -Jeremy
Your cleaning process seems pretty sound. I probably would have done about the same thing. I think it's a big improvement to not be covered with those deposits. Once it starts to tone up again it'll look even better.
In a single day's work? Wow. I've seen some other impressive results with Na Thiosulfate such as @JayAg47 's owl tet and a few others
Sodium thiosulfate ("hypo", the photographer's "fixer") dissolves horn silver (silver chloride); mild acids dissolve silver oxide. Neither will damage good quality silver if used in moderation, but acids may leach copper from the surface of poorer quality silver leading to surface silver enrichment. Ross G.
