Stinky coin, wash-off toning

[Heliodromus]

When Vespasian said "Pecunia non olet", he evidentially hadn't met my coin. Not only was he 250 years too early, but it probably didn't stink back in the day. But it does now, smell-wise at least.

So, I just received this coin, auction photo below:

 

On inspection under a 10x loupe I noticed a couple of small potential BD spots that'd weren't there in the auction photo. I decided to give it a rinse with soap and warm water (which I often do - harmless to coins) to see if it came off, and unfortunately it did, although there's no visible damage to the coin at this stage.

What I also noticed from handling the coin was that it had a strong and rather unpleasant chemical smell, which transferred to my hands and wouldn't come off when I washed them.

I decided to give the coin a slightly better soap+water wash to try to get the chemical smell off, to no avail, but then saw that that much of the dark toning had come off revealing the stripped bronze underneath. At this point I gave it a further rinse in acetone to try to remove the smell, which it mostly did, as well as removing what litle was left of the artificial toner.

Here's the coin now, after it's soap+water and acetone baths:

 

Looking at the edges of the coin, there is some remnants of a thick dark green patina, giving an idea of what it may have started out like before being stripped and stinky-toned.

The coin wasn't cheap, but it's an unlisted bust and mint state, so I'm not going to try returning it. I'll probably just let it retone naturally. I'm more concerned if that was real BD, and if it comes back. Any suggestions for best treatment for a coin of this type if it does?

The coin came from the same NN auction house as PNO CEO Per D's wash-off-toning coin, so appears to be something they are using. Really have to wonder what it is given the nasty smell! Buyer beware of these dark toned coins.

[Victor]

After soaking (I usually use washing soda), I typically put suspect coins in the oven at low heat to make sure they are very dry and then back in the tray...just check them periodically to make sure nothing is going on.

[Nikko]

Here a similar case I had some months ago. I returned the coin the seller (a professional one on Ma-shop).

Two little spot of bronze desease appeared a few days after I received the coin. I gave the coin a distilled water bath. The result was terrible.

[Heliodromus]

I never would have suspected these coins had been totally stripped until this experience. The slight color variation gives the appearance of their being more underlying silvering than there really is - it's just the appearance of the dark artificial toner on top of some surface color variation of the bronze itself. On my coin the only actual silvering remaining are a couple of small spots such as under Licinius's eye, and under his chin line.

Nikko, I'm curious, did your coin have an unpleasant chemical smell too? If multiple vendors are selling similarly treated coins, I wonder if they are doing it themselves, or perhaps getting coins from same supplier?

Given the smell of my coin, the artificial toner must have been recent, presumably as was the stripping, which is why these are a gamble for appearance of BD.

[Per D]

Here is a third example. This follis came from the same auction as the one I posted last week, and it also started to develop bronze disease. After a couple of days in distilled water, the glossy surface turned sticky and whatever stuff had been applied comes off with a gentle rub.

The fake patina doesn’t seem to have been hiding a completely stripped coin, but an uneven toning (and possibly the remains of a treated case of BD). Giving NN (pun intended) the benefit of the doubt, I suppose this could be the work of a previous owner.

No funky smell, but the soaking water turned bright turquoise (I've noticed this happening with other bronze coins, even ones without this fake patina).

[Heliodromus]

Hmmm... and here's the 2nd coin I bought in same auction as 1st one, which on inspection also has BD appearing. No smell on this one, but I assume same wash-off toning (I'm not going to touch it until I decide what to do with it).

I'm rethinking whether to keep them.

Auction photo:

 

As received:

 

Per, are you keeping that one too? What are you doing about the BD - just the distilled water soak, or any treatment ?

[Per D]

Yes, I won't try and return coins I've been meddling with, but was thinking I should inform NN about this discussion.

For the past few monhs I've been experimenting with several BD coins. I cleaned most of them with acetone as well as soaking in DW before using a scalpel to get rid of the green stuff. I've seen several experienced people recommending subsequent treatment with sodium sesquicarbonate or (the highly dangerous, carcinogenic) benzotriazole. So far, I've only used plain baking soda followed by a rinse and slow 'baking' and it seems to work, but time will tell.

[Nikko]

Ben, i can’t remember the smell but it had a “wet paint” appearance.

Hundreds and hundreds of bronze coins sold every months and almost all of them with the same dark green patina… it’s suspected…

[Victor]

I have a few of these NN coins with the same appearance. It seems like some sort of varnish...it reminds me of old collection coins that were shellacked, though not as tacky. I don't think NN did this; but is selling a large collection. I haven't had any problems with mine.

[Heliodromus]

So, I've decided to keep both coins. Lesson learned in terms of trying to understand auction photos. In over 1000 coins, this is my first encounter with BD.

The 2nd coin, as suspected, also had the artificial toner which came off with soap and water and a few min in acetone.

Here's what it looks like now:

 

I see it's easy enough to buy sodium sesquicarbonate on both eBay and Amazon, although good to hear you're both having good results with alternatives. I may try baking soda first since I already have that at home. I may buy some Ren Wax since I've read it's good to seal coins after treatment.

I'm really curious what that nasty chemical smell was on the first coin. Hopefully nothing nasty like benzotriazole, since Google seems to indicate its odorless (surprising - I'd have expected anything benzene based to have a smell). I'm guessing the chemical smell was from the artificial toner rather than any prior BD treatment that might have been applied. I rather doubt it's "old cabinet smell" though  - seems like something that must have recently been done or the smell would have dissipated.

[Per D]

I'm really curious what that nasty chemical smell was on the first coin.

I haven’t got a clue, but I reacted when you first mentioned the smell. Last night (!) I brought out a follis that’s been soaking in distilled water for a couple of months. I’ve been rubbing it with a Q-tip every now and then and thought all of the artificial toning was gone. It wasn’t: some kind of chemical reaction must have taken place recently, and rust-colored stuff came off easily, leaving a pink, naked surface. The coin also smelled horrible (think wet woolen socks dissolved in contact cement). 

I may buy some Ren Wax since I've read it's good to seal coins after treatment.

I would wait a while before applying wax in case the bronze disease comes back.

[six2ten]

Here’s another example of bronze disease developing, this one from NN 110 in November. Auction photo followed by a composite image of the the coin with BD and then after treatment with home-made sodium sesquicarbonate. I didn’t notice any odd smell, and I reckon the BD started developing in less than 4 weeks. No new BD after 5 days of final soak

[Victor]

I have been keeping an eye on my NN coins and, surprise, found three starting to turn green. Below is one with original auction pic and after cleaning pic. I soaked it in sodium bicarbonate for 24 hours, then baked it for about 2 hours, then applied some renwax. Of course, I will continue to monitor them.

[Heliodromus]

Seems like Naumann have a coin pandemic on their hands.

I've still got my two in quarantine, but so far so good. I never did anything additional to them other than original washing off of the artificial toner and v.brief (5 min?) acetone bath. Maybe the real test would be if they were in a more humid environment - summertime perhaps.