Bronze disease (naively thinking I was immune)

[Per D]

I live in a fairly dry climate and haven’t had much problem with bronze disease. Over the years, I’ve actually purchased a few coins with suspicious spots or a ‘dusty’ surface, but they’ve stayed stable so I haven’t attempted any kind of treatment.

This past month there have been several, sudden outbreaks in my trays, however. I don’t know if there is something in the environment causing this, or if I’ve just had bad luck.

The latest example is a typical one: a follis that I bought in July without noticing any other problems than the pockmarks on the obverse. The first photo is from the auction catalogue and shows what the coin looked like just a week ago. I took the second picture this morning, before letting the coin soak in distilled water.

12 hours later, the water looked scuzzy, and rubbing the coin’s surface with a Q-tip removed most of the green stuff. There are still plenty of very small crystals all over the surface, so I’ll have to decide on some more radical course of action. Most of the dark, glossy ‘patina’ also came off.

The affected coins come from different places but have at least one thing in common: all seem to have been thoroughly cleaned (probably stripped down to bare metal) and then artificially toned. While the crisp look of such coins can be quite attractive, I think I’ll be more careful in the future, though. I also wonder what kind of stuff people use for re-toning their coins that can be removed by distilled water and some gentle rubbing.

[Nikko]

Can I suggest to return that coin to the auction house? 

[Heliodromus]

The affected coins come from different places but have at least one thing in common: all seem to have been thoroughly cleaned (probably stripped down to bare metal) and then artificially toned. While the crisp look of such coins can be quite attractive, I think I’ll be more careful in the future, though. I also wonder what kind of stuff people use for re-toning their coins that can be removed by distilled water and some gentle rubbing.

I'm not sure ... Most of the auction houses selling repatinated coins at least use a stable heat reatment. I'm increasingly fussy about this - I don't like the look of the gray/brown repatinated coins so common from some German sources, and would prefer an honest untreated coin with deposits. I've heard BAC is infamous for abusing their coins.

The only time I've had an artificial patina/toning come off is on the coin below. I often (fairly gently) scrub my coins with liquid soap and a toothbrush as part of the onboarding process, and on this one the toning came off completely leaving it butt naked! I'm guesing Deller's Darkener or something similar.

Seller's photo

 

After soap and water cleaning

 

In hindsight I never should have bought the coin in the first place, but that was back in 2005 when I'd only been collecting for a couple of years.

[Victor]

I also wonder what kind of stuff people use for re-toning their coins that can be removed by distilled water and some gentle rubbing.

a product called Jax can be used to give a variety of patinas, including brown and green, and it can be easily removed.

[Heliodromus]

a product called Jax can be used to give a variety of patinas, including brown and green, and it can be easily removed.

Havn't heard that name in a long time, but you're right. Deller's is sulphur-based, so reacts with the bronze and presumably doesn't wash off.

I should probably re-jax my coin, then sell it! It looks awful as is!

[Per D]

Thank you for your input!

It’s probably too late to return the coin, especially as I’ve been meddling with it. I actually don’t mind keeping it, even if the patina/toning will be ruined in the process of trying to halt the BD corrosion.

When it comes to deposits and thick and/or uneven patina, I’m really of two minds. In general, I think it’s best to leave ancient coins as they are (whatever that means) while also realizing that cleaning, smoothing, minor tooling, re-toning and so on are much more common than I used to believe.

Below is an example from my collection where the cleaning probably went a little too far. The first is the seller’s photo, the second is from the ROMA’s e-sale where it sold a couple of years ago. I suppose the coin looked quite bad when it was dug up (and I wonder if the missing piece was amputated during an earlier cleaning).

Heliodromus’s coin is interesting: it’s been brutally over-cleaned, but the details are also beautiful. It shouldn’t be difficult to find a buyer, especially if it’s been Jax’d or treated with liver of sulphur or something. (The coin doctors at PNO Numismatics wouldn’t hesitate to spray it with gold paint and sell it as an unrecorded solidus, of course.)

As for BAC, I haven’t followed their auctions closely, but I remember they sold many, many aureliani a couple of years ago. The coins probably came from the same hoard as all had the same appearance: intact silvering under a thick layer of that green stuff that comes off with patience, skill and a scalpel.