Hieronymus of Syracuse - restoration of a valuable coin

Together with a friend, I bought this coin of Hieronymus of Syracuse, with the intent of restoring it, and then resell it:

HIERONYMUS OF SYRACUSE, AR 10 Litra (215-214 BC)
Diademed head of Hieronymus left / ΒΑΣΙΛΕΟΣ IΕΡΩΝΥΜΟΥ above and below winged thunderbolt, MI above
8.43g

The problem is obvious: a thick layer of horn silver on the reverse, and some spots on the obverse. However, there were several indications that it would turn out well:

1) on the reverse, at 4'o clock, part of the horn silver was gone, revealing a smooth and nicely patinated surface

2) on the reverse, at 7'o clock, the border between smooth silver and deposits was rough

3) overall, the coin was in good condition with very minimal pitting.

I treated the coin the usual way, however, this time a bit nervously since CNG already estimated hammer price which was rather high. Also, the coin was bought not only by me, but also by my friend ...

I dropped the coin in a sodium thiousulphate solution, and it immediately turned black (which is a good sign):

... also visible are the small parts of horn silver that fell of the coin.

After 10 minutes, I removed the coin from the solution (now completely black), and rinsed it under tapwater. The dark layer (Na3[Ag(S2O3)2]) is easily removed, revealing the nice grey patina below (AgS):

( a bit yellow due to bad lighting in the evening). There were still some minor deposits left, e.g. at 4-6 o'clock on the reverse.

This morning, I repeated the treatment:

... with- this as a final result. Suffice to say I'm happy with the results! The final deposit at 3'o clock (the brown deposit) is iron oxide (i.e. rust), which is very difficult to remove, so I'll just keep it this way.

 

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That is a very good result, and it almost sounds like an easy process.

But is it really?

So you just gave it a couple of baths and a rinse? Is that sodium thiousulphate solution commercially available and easy to get? Is it only for horn silver or can it be used for general coin-cleaning?

Sorry for all the questions And the final one, do you think that you increased the coin's value considerably? It certainly looks like, but I don't know how much horn silver damage usually reduces a coin's value. I guess it depends on how easy it is regarded to fix the coin, but as I said you made it look easy

 

Thanks @Only a Poor Old Man. To answer your question: yes, it is relatively easy, but recognizing which coins benefit from cleaning, and which don't requires a learning curve. I've cleaned quite some silver antique coins so far, but no cleaning project is the same.

This one I expected to react quickly, for reasons mentioned above (and other, more subtle signs that are not really visible on a photo). Sodium thiosulphate is readily available and not too expensive, as is distilled water. It's only suitable for horn silver, and will react only with AgCl or AgBr (whichever is present on the coin) - so it will leave the patina intact.
The dark layer Na3[Ag(S2O3)2] is easily removed by gently rubbing the coin. In some cases, it's a nice method to repatine coins with horn silver that were heavily cleaned: the horn silver disappears, and a thin greyish layer stays.

Regarding whether or not the value increased: I have no idea. I guess it has. We will find out how well it sells, but since we obviously have no control coin (i.e. an uncleaned coin of similar quality), I can't draw any conclusions.

 

Congrats on a sensational job of restoration ! Knowing this process doesn't depend on abrasion makes it a valuable solution . This is a great alternative to brushing & smoothing .

 

Congratulations on a great job. I think you've definitely enhanced the coins value.

I may have to try this method. How do you determine the solution? Is there a specific ratio?

 

That is really awesome! Thanks for sharing and great work!

 

Thanks for sharing. The coin looks nice after cleaning.

 

Fifty years ago you could buy Sodium thiosulphate in almost any drugstore and every camera shop since it was photo 'fixer'. Then someone invented 'Rapid fixer' which was better for pictures but not useful for coins and it became harder to find the old stuff. Later still digital photography erased terms like fixer, film and darkroom from the vocabulary. Progress has its price.

 

Hi @gsimonel, if you search for "horn silver" and filter on my user name ("roerbakmix"), you will find several threads where I post a more detailed description. There is no standard procedure. The most difficult part is to determine whether the coin will benefit from cleaning.

In the Dutch city where I live, there are some specialized drugstores - I guess it has to do with their being a university. However, you can readily find Sodium Thiosulphate online and somewhat cheap. Chose the 'anhydrous' solid form.

 

Beautiful coin! What a difference between the first and last picture!

 

Will do. Thanks.

I was able to find it quite easily over the internet. It is not expensive. I've ordered some and will try it out when it arrives.

 

Thanks all for the compliments. Feel free to post coins with deposits that you consider to clean, if you want my advice (or someone else).

Another recent cleaning project, which was relatively easy:

Green deposits, mainly on the reverse (under the tail), due to PVC degradation. Easily removed with white spirit (or, alternatively, use acetone).

The coin seems more shiny, which isn't the case, but due to bad lighting.

Also, a while ago, I restored this gros tournois:

Apart from spotty horn-silver patina, the coin was bent on two axes:

I first removed the patina, then heated the coin to c. 800 C (!), applied slight pressure, reheated, applied pressure, etc. until flat:

 

That's a fantastic restoration job.

Sorry I have a question since we're talking about horn silver.. are the black deposits on this Vitellius denarius horn silver? There's a mottled look on the reverse so I was thinking it might be.

 

Hi Richard, definitely horn silver. The rough surface around is not a good sign. The sharp margins and the scratches are indicative of mechanical cleaning - you can see the effect on the legs of Mars (?) on the reverse. Chemical treating will remove the horn silver, and likely a couple of scratches as well (which are in the horn silver, and not in the coin below). However, it's hard to tell how the surfaces below the horn silver will turn out.

I would give it a try, but carefully.

 

Well done, that's a fantastic result!

 

Thanks @AncientJoe!

 

I bought some on Amazon a few years ago and I'm sure they have more.

 

That's a pity. I imagine the coin looked amazing when it was uniformly covered by horn silver.

 

The result looks great!
What exactly happens chemically when doing this process? It doesn't affect the surface of the silver?

 

AgCl + 2Na2S2O3 → Na3[Ag(S2O3)2] + NaCl

https://chemiday.com/en/reaction/3-1-0-2154

also, the relation between temperature and the solability:
https://saltlakemetals.com/solubili...ulfate Solubility,when the solution is heated.

It doesn't affect the surface of the silver. What's more, it doesn't dissolve the 'true' patina (i.e. AgS).