Numismatic and History Discussions > Uncleaned Ancient Coin Discussion

Treating rust looking breaks in patina

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Ken W2:

Hello all: Here is an Aurelian Genio Ant I just finished mechanical cleaning on yesterday (19.09 mm 2.82 gr. Can you believe that in 270 even silver washed that little thing was accepted as the equivalent of two silver denarii issued 100 years earlier likely weighing 6-7 grams and being 90% plus silver, but I digress) and an VRBS ROMA she wolf coin I’m still working on. Both have rust looking breaks in the patina—just in front of the face on the Ant and in several areas on the VR. These breaks were already there when I started, but grew a little as I cleaned around them, mostly on the VR coin. If these breaks showed clean, bare bronze this would be an easy call— live with it and let it darken naturally or touch it up with Jax or LOS— depending on the camp you’re in. I have been leaving these type spots alone and just waxing over after final cleaning and drying.  But is there a chemical treatment that won’t harm the patina but will remove or harden/darken these “rust” spots ? If this was an iron Civil War artifact the last step before waxing would be a phosphoric acid wash which effectively treats any remaining small rust spots or flash rust. But acid not an option with these bronze coins. Any ideas how to treat these “rust” spots?

Ken W2:

CORRECTION:  That a FIDES MILITVM reverse Ant. I confused it with a Severus I’m working now too.

Ron C2:
In my opinion, if you are going to Ren wax them, I'd dry them well and use the wax. That's it.


These are not rust spots and have nothing to do with Fe.

The can be caused by two things.  A layer of the green oxidized AE suffice breaks off revealing metal underneath which then begins to oxidize, but is "behind" in the process.  Or, a spot where a BD reaction has stopped resulting in a rust-colored blister.

The VRBS ROMA looks like the former - the surface has broken through.

The Aurelian might be the latter - arrested BD - hard to tell from the image.


Ken W2:

Thanks fellows.

Shawn, I assumed it was not iron related rust-- while there probably is some trace iron in the alloy it's likely not enough to cause real rust to this extent.  But, if I knocked a little of the green layer off either coin there would be this rust colored layer beneath it too. (That's how these spots grew from smaller ones initially).  It's like there is a layer of corrosion underlying the green layer.  I think I'll try a soak in a 5% sodium sesquicarbonate on the VRBS ROMA and just see what happens-- I'd like it to be darker and not rust looking.  I don't think that will do any harm, and if it does it won't be any great loss. Thanks again.



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