Afternoon everyone, Can you assist as the how best to proceed with this recent acquisition? I understand the redness is oxidisation, however, do I attempt to clean (distilled water,q-tip) or do I just leave well alone, or do you have any further advice?
Leave well enough alone. As you can see from the reverse and the high points on the obverse, it's already been harshly cleaned, exposing bare metal. There's nothing left to clean. Red oxidation like that, in my experience, doesn't tend to come off with any amount of scrubbing.
Yeah, I'd leave it alone. In my limited experience, that reddish patina seems pretty permanent - which is to say removing it would probably lead to destruction of the coin's surface. Perhaps an expert "smoother" could work wonders, but I wouldn't try it myself. Sometimes the reddish patina is attractive. Sometimes not so much. Here is a Marcus Aurelius sestertius that has an unpleasant case of the "reds" - it seems pretty permanent to me:
I am intrigued. Though I have some experience cleaning silver coins, I hesitate from cleaning bronze. Yet, I'm interested in this 'red oxidation'. Does anyone have ideas what it actually might be?
There are 6 kinds of patinas that occur on copper: Equation 1: 4Cu + O2 → 2Cu2O [red to pink] Equation 2: 2Cu2O + O2 → 4CuO [black] Equation 3: Cu + S → CuS [black] Equation 4: 2CuO + CO2 + H2O → Cu2CO3(OH)2 [“malachite,” dark green to blue] Equation 5: 3CuO + 2CO2 + H2O → Cu3(CO3)2(OH)2 [“azurite,” blue to purple] Equation 6: 4CuO + SO3 + 3H2O → Cu4SO4(OH)6 [“brochantite,” dark green to emerald]
Ok, so LEAVE is the answer and kind of what i was thinking. I love the underlying coin itself so i will retire it to a paper envelope and look for an opportunity to post it again sometime in the future, perhaps on another serpent thread? Grazie.
Leave it alone. The bronze parts are already overcleaned. The red stuff will be impossible to remove and trying will only damag the coin further.
I would leave it alone, too, but only after I squirted a little 3-in-1 oil on a soft rag and tried rubbing some of the oxide off, most likely discovering that it didn't help much. Sorry, but I can't help trying stuff like that.
There is also tin and other metals in ancient bronzes that also form multiple compounds, making cleaning them chemically more difficult. I agree that the red is probably mostly copper oxide, and it can only be removed by strongish acids or electrolysis, both of which will leave pitting. Just enjoy it the way it is. John
Interesting link. Does this mean you should soak the coin in salt water or leave it outside? Ken Dorney was giving updates on a coin he placed on a roof.
These Nemausus coins tend to have a high content of tin in them. They seldom really rot, but cleaning can only be done here bij stripping it completely, which will remove the oxides, but will leave a rough surface.
