How to remove EXTREME encrustations?

These coins have something quite nice underneath, but there’s basically rock crystallized in the surface.

What’s the best approach?

 

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This will seem like heresy to many, but in my archaeology class we were sometimes successful in removing these with citric acid or hydrochloric acid. You can also spot apply it by dropping it onto the areas you want to remove with a toothpick, but this requires many repeated applications and great patience.

Whether it is a good result or not will just depend on to what degree the metal beneath has been damaged by the corrosion. The acid will turn the corrosion product into a sticky green slime, which can be removed by brushing. I don’t recommend this unless the coin is otherwise not identifiable or salvageable.

 

I do have some lemon juice, I suppose I can start with that. No HCl on hand, but I'm sure I can find some somewhere

 

HCl is also known as Muriatic Acid.

 

I would not use any kind of acid at all. I would first try multiple soakings in distilled water changing out about every 3 days or so for at least a month and then try to start working the crust off with a wood tooth pick or something else made out of wood.

 

Personally, with encrustations like that, I've had very good results by spot treating with lemon juice. In my experience, distilled water won't be enough to do anything with that kind of encrustation. Just put some on and scrub it. Do that multiple times a day for a while, and if you're patient you may have very good results. My instructor swore by HCI, but I feel like it does better if the entire coin is a near slug with no visible design.

 

Those deposits look, as you say, rock hard. Removing deposits like the one on this coin is problematic, especially for bronzes.

Muriatic (hydrochloric) acid is very powerful and must be used in diluted form, preferably pre-diluted. This is a very hazardous acid to use, and it is best used in a laboratory. The fumes are especially hazardous. It you're intent on using acid, please be careful, and use protective items, including gloves and face protection (googles). Use this acid in a well ventilated area, and avoid the fumes. I never used this acid on any coin, and I would hesitate to do so now.

I would start conservatively, with a very long soak in distilled water. See if anything comes loose with the aid of a toothpick. Some older collectors and dealers used to soak coins in olive oil for several weeks or longer. You could try that approach as well.

I view this coin as a situation of mitigation, at best. If you can remove some of the deposits, without damaging the nice patinated areas, that might be the best that can be done for this coin.

One more approach, that does use an acid, is Naval Jelly. This is a readily available and popular rust remover. Care must be used when applying to the coin; apply only to the affected areas. Leave it on for about 10 minutes or so maximum, then try to dislodge the deposits using a wood toothpick. Rise the coin with distilled water and examine. Repeat the process until you reach the point where you're satisfied with the results. Don't leave this acid on the coin too long as it will eventually dissolve all deposits and expose bare metal.

I normally do not use Naval Jelly on bronze coins (really only when dealing with bronze disease). It is more effective in some cases on silver coins with earthy deposits.

 

Does anyone here think that soaking a coin with distilled water will remove hard green patina (encrustation)? Not being rude or funny but AFAI thought I knew you can soak that coin in water for ten years and not take a hard green encrustation off.

Anyone have any success with this suggestion?

 

I have found Muriatic acid to be extremely valuable for some types of U.S. coin conservation. I've got a great big bottle of it. I wish I could add more.

PS I shall try it on a "green" ancient bronze coin. Thanks.

 

The concentrated solution can have irritating corrosive fumes, but the diluted solutions are easy to use. I keep a dropper bottle around.

BTW, Naval Jelly is a mix of sulfuric and phosphoric acids with some thickener to make easier to use.

 

I am merely suggesting to start conservatively and move forward to more aggressive methods.

 

Naval Jelly action is mainly by Phosphoric acid 15-30% ( actual % is a trade secret, but I think it is in the higher range).

This is why some old old timers use to ( and maybe still do ) use CocaCola (tm) as it s a somewhat less concentration of the acid although they downplay

http://archpdfs.lps.org/Chemicals/Naval_jelly_rust_dissolver_Loctite.pdf

 

Simple:



Just be safe, and wear protective gear.

 

It is possible to completely strip a patina, including such extreme encrustations, by letting the coin sit in a solution of sodium hydroxide (lye) for a while. Sodium hydroxide is commonly sold as a drain cleaner. It doesn't attack metal as more aggressive acids do, but it will dissolve about all encrustations. Rinse your coin thoroughly and let it sit in lots of distilled water for a while after giving it this brachial treatment.

Honest warning 1: Sodium hydroxide is very dangerous to handle. It causes extremely nasty caustic burns when it comes in contact with skin, blindness when it gets into your eyes, and, in the worst case, painful and slow death if you swallow it. It is thus best handled only in a laboratory environment. Always wear at least protective gloves and glasses when even coming only close to such substances.

Honest warning 2: Sodium hydroxide will strip bronze coins of all patina. You never know what's below the patina, but it surely won't be an immaculately smooth and attractive metal surface. In the best case, you'll get a result like the coin below, which had encrustations similar to yours and spent two days in a weak sodium hydroxide solution. In the worst and more common case, you'll get an unrecognizable slug.

Honest warning 3: The need to use such cleaning methods and their mostly unsatisfying results were a main reason why I stopped buying uncleaned coins.


Constantine II Iunior, Roman Empire, AE4, 335–336 AD, Siscia mint. Obv: CONSTANTINVS IVN NOB C; bust of Constantine II, laureate, cuirassed, r. Rev: GLORIA EXERCITVS; two soldiers, helmeted, draped, cuirassed, standing facing each other, each holding reversed spear in outer hand and resting inner hand on shield; between them, a standard; in exergue, ESIS. 16mm, 1.60g. Ref: RIC VII Siscia 253.

 

Wow, when I was a kid, my Grandparents had an outhouse on our Farm. We used to dump LYE into the hole over the pit to clear up the soil we contributed to. (We would buy sacks of it at the Hardware / Farm & Feed store)

Wow, purdy scary that we hung our collective Asses over that pit!

RI
Augustus
27 BCE-14CE
AE As or Semis (Half-As after a Lye treatment???)
Spain
Celsa Mint
29mm 5.0g
Laureate Augustus -
Bull (lost his As after a lye treatment?)
RPC271
Cut in ancient times to make change

 

Even when I'm using Draino on my sink? Actually I mostly agree, concentrated bases concern me as much if not more than acids.

 

Are you sure you used lye (sodium hydroxide) and not lime (calcium hydroxide)? The latter is often used in outhouses etc. It's still caustic, but not as much as lye.

@Kentucky – yes, I personally do wear protective gloves and lab glasses when using clog remover. You can call me overcautious, but together with getting bleach in one's eyes and unpurposely drinking antifreeze, drain cleaner accidents by far lead the top ten of most common serious chemical injuries in the household. I'd rather not be a part of that statistic...

 

Perhaps they read that notorious magazine article in the early 1960s that claimed that you could dissolve a fork by leaving it in a glass of Coca-Cola for a few days.

 

My grandmother always soaked ham and turkeys in coke, because it tenderized the meat.

I do not drink coke nor ever use meat tenderizer... if it has THAT affect on meats, what is it doing inside ME?

 

Great question! I do remember lime, and I do remember lye as a kid growing up. Perhaps lime was for the outhouse.

He also had dynamite and blasting caps. I always wanted to toss a lit one down into the pit.