What's the best way of removing hard red deposits on a silver coin?

Hello everyone!

I was reminded of having this coin by a recent thread about Gallienus. It is a rare VICT GAL AVG type.



Unfortunately, the surface has a lot of hard red deposits one, along with some green ones. I doubt the green is bronze disease, as it is quite hard, and the coin is (at least somewhat) silver.



Is there any way of getting these deposits off the coin? I was wondering if lemon juice would work (as it should do for silver coins), but I don't trust the silver quality of Gallienus' coins enough to know if that would do damage to the coin

Any ideas would be greatly appreciated!

Thanks!

 

Log in or Sign up to hide this ad.

That’s a rare enough coin where I wouldn’t try any cleaning beyond a gentle brushing to remove any loose material. Otherwise, I’d leave it as is… or pay someone who knows exactly how to clean it without ruining the coin. It’s a great coin, I’m jealous! Keep it as-is.

 

I've never seen this reverse type before! After some quick google-fu, I found your original thread on it haha.

I would do what @Orange Julius and just give it a light brushing at best to remove anything loose. I wouldn't want to run the risk of scraping any of the patina off or exposing something that would further lead to damage.

Beautiful design. Thanks for sharing!

 

The few times I've tried to clean bronze coins, the red stuff was much more difficult (impossible) to remove than the other types of minerals or deposits. I'd take OJ's and FF's advice.

 

Cleaning coins and banknotes was never my specialty. In fact, every single time I tried cleaning a coin or banknote (yep, I managed to ruin some notes too) the end result was worse than the original.

I have seen here on CT collectors doing a fantastic job with cleaning coins.
On yours, I'm afraid that cleaning this one might make it much uglier (and nope, I don't think it's ugly at all).

The red deposits add personality to the coin IMO and they don't hide any design elements. Especially since the coin is not common, I would advise to leave it exactly like this.

 

I agree with the previous comment. I generally assume that whoever cleaned any given coin before it came into my possession probably had more experience and stopped where they did for good reason.

 

I have encountered these red deposits on Gallienus' coins before. Personally, I don't think they add anything to the coin. Instead, they are ugly and they take away from the coin. However, I found that these deposits are (nearly) impossible to remove (without damaging the coin), so I would leave the coin as it is or consult a real expert.

 

Iron oxides and difficult to remove. Check my post history for several examples.

If you live nearby, I would happily restore it for free. Send me a pm.

 

This red corrosion product is extremely hard and as such difficult to remove. While it can be removed with repeated acid baths and brushing, this is not to be recommended, especially for low-purity silver. Mechanical removal is usually necessary - this is time consuming, requires a degree of expertise, and may expose subsurface pitting.

 

The red is probably cuprite which often forms in associating with green malachite. You can always think of the coin as a cross-over collectible, not only a scarce Roman coin type but an interesting mineral specimen!

 

If it's Iron Oxide, then sodium thiosulfate is my go-to treatment.

Here's a limes Caracalla of a low silver billon:


After a week or so soaking in sodium thiosulfate:


After Ren Wax:


As you can see, the thiosulfate removed 100% of the iron oxides, while maintaining the overall integrity of the fabric of the coin.

 

What test do you use to distinguish iron oxides from the much more common reddish copper oxides?

 

I guess I just take a look, if it’s orangeish and rough textured, then it’s usually iron oxide.
The real test is seeing of thiosulfate has any impact, it’s the trial by fire

 

let it be, it's old and beautiful as is. after cleaning it would you REALLY be happy?

 

Those deposits look like accumulations of cuprite, Cu₂O, an oxide of copper. They are extremely hard to remove and I don't recommend even trying; the coin would probably be worse off attempting this.

I say leave as is. It is a rare coin.

 

That’s too bad, copper oxides (except foe the green stuff) are just about inert. Bummer

 

That's right - they are inert, and they are hard as concrete.

I imagine that the coin must have been in a hoard, and moisture and soil conditions lead to a steady accretion of this oxide over the hundreds of years the hoard was buried. This coin itself is billon, so there is plenty of copper in alloy of the coin itself to react at points that it was in contact with other coins made of billon or bronze.

 

I’ve had some coins with the inert oxides. After abuse from sodium hydroxide, vinegar, lemon juice, thiosulfate, and naval jelly, the end result was chemical burns and a ruined coin. Haha

 

Clearly a case where the cure killed the patient.

 

Thanks for your help, everyone! I think I'll leave it as is.

Thanks for your offer! I'm in the UK though, so I doubt I'm nearby. Thanks anyway