Quick question to the group... I have this Victorinus that's been sitting in a jar as a "give away" or "sell" coin for years. It was struck by a very worn reverse die but it's still not a junk coin. I ran into it today and wanted to take a run at removing the green encrustations on the obverse. Under the green is smooth coin, not corrosion. The encrustations are too strong for mechanical removal without gouging the coin itself... so I was hoping to get some recommendations for soaking it in something a bit stronger than distilled water (this coin sat in DW for 6 months a few years ago with no success). I've seen acetone, vinegar, lemon juice... and others as possible solutions. Anyone have experience with removing these types of encrustations? What works best without pitting the coin or stripping the patina? Thanks!
Yeah that’s what I was thinking too... I understand lemon is often used for silver and not bronze but had also read that “spot” usage (only on the green) can work but I doubt I could keep anything to just on the green encrustations.
Short of mechanical removal (which will not look good) you have to use an acid or base. Lemon juice or ammonia will work. Just use short soaks, dabbing with a cotton swab periodically. When the copper carbonate (green stuff) has been removed, rinse the coin and neutralize it in the opposite solution (if soaked in lemon juice, soak in ammonia or sodium bicarbonate solution, or vice versa). After that, put the coin through a few distilled water soaks and then dry thoroughly. Here's one that was successfully soaked in lemon juice, or maybe it was white vinegar. Whatever-- both are weak acids and that's what was needed: Note that the deep scratches on this coin were on the flan prior to striking. They are not cleaning scratches. These lines are a typical finding on Black Sea bronzes-- "flan adjustment marks". Results can and will vary, as the composition of ancient coins is of course not consistent. I think coins from Pontos (like the coin shown above) and other Black Sea bronzes have a composition that is more forgiving of such treatments. Another option is to send it to someone who is experienced in cleaning. Ask @Alegandron about his experience. I sold him a Postumus/Sol antoninianus that was covered in "malachite" which obscured the devices. He sent it to someone for cleaning and now it looks fantastic!
I’ve had some luck soaking copper-based “greenies” in olive oil, but it’s a slow process, sometimes taking several weeks for stubborn cases. (There are some who use this method who insist that only the highest grade extra-virgin will do, but at my scandalized wife’s insistence I switched to our cooking-grade stuff with no apparent change in results. As they say, your mileage may vary.) D.
I've had some luck using lemon juice to remove unsightly green encrustations. It can be applied to small areas using a toothpick or skewer. I usually put it on for a minute or two, rinse, scrub lightly, and see what it does. If it doesn't progress, leave it for longer periods. Just be very careful. It may also depend on the bronze alloy. It's something I've done as a last resort and had okay luck with.
My only real success with copper was using potassium hydroxide which was the basis of one of the older gone and lamented coin care products. Sodium hydroxide (lye) should have a similar effect, but be CAREFUL since these strong bases can disslove your skin. Use only dilute solutions and rinse your hands thoroughly after using. Perhaps start with some soaks in sodium bicarbonate first and see what that does (bicarbonate of soda, baking soda). Let us know how it goes.
I'm not an authority on this. I wonder what effect Hydrogen Peroxide deluded somewhat with water would have on the coin.
If it were mine I would plop it in a small glass bowl, use enough hydrogen peroxide to cover the coin. Put it in the microwave for 10 sec. Let it bubble away. After about 20 minutes, brush lightly with a soft bristle toothbrush. Not saying you should do this but I would if it were my coin.
I use for many years virgin olive oil because 1) the “extra” virgin oil contains a lower acid level (less than 1%vs 2% or more) 2) it’s cheaper to buy 3) like you @Magnus87 I want to keep the peace in the family...
I never clean my coins, nor do I really have the desire. However, a friend offered to clean one of mine. I trusted his method as he is a pro. Here is the Postumus that I purchased from @TIF . Later, @YOC cleaned it for me (professional formula developed by him.) Before: RI Postumus 259-268 CE Antoninianus Cologne Oriens GREEN Compare the before and after unexposed silver spot at 11-12 o’clock on the edge of the coin. Cool. After @YOC 's cleaning help: We had NO clue that it was this well silvered. Please forgive my poor pic. I need to shoot it, but is locked up now.
Not seen him here for some time. He used to be active, but haven’t seen a posting for a couple years.
