How to remove 'encrustation' from R.R. coin??

This silver R.R. coin of mine has an encrustation on it and I was wondering if anyone would be able to tell me how to remove it, please.
Is there a way to remove it safely, without damaging the coin?
I am sure that other collectors will have had coins with this sort of encrustation on them and I was wondering if they could advise on how to remove it, or should I just leave it on there, perhaps?

 

Log in or Sign up to hide this ad.

Looks like horn silver... as far as I know it can't be safely removed.

 

@Roerbakmix has experience removing horn silver. I'll let him tell you about it .

 

Thanks @TIF. I agree: it sure looks like horn silver. As mentioned before, I'm in the process of writing a detailed guide on the restoration of coins with horn silver, but my 1.5y/o twin in combination with finishing my PhD is not really beneficial this. Anyway, here is a similar example of horn silver on a Sev. Alex denarius:


And below a timelaps of the same coin in a solution of sodium thiosulphate.



Your coin has been cleaned before, both mechanically and chemically as can be seen by the scratches (mechanical):

... and the somewhat porous appearance of the silver that was beneath the horn silver. It was probably treated with an acid, which is not very effective on horn silver. Sodium thiosulphate however, is.

I'll copy paste my cleaning steps for horn silver below:

Chemical cleaning

Probably the easiest and safest method to remove horn silver is by using a solution of sodium thiosulphate (2Na2S2O3). Both AgCl and AgBr dissolve in sodium thiosulphate, as can be seen from the following reactions:

§ Silver chloride (AgCl): AgCl + 2Na2S2O3 → Na3[Ag(S2O3)2] + NaCl

§ Silver bromide (AgBr): AgBr + 2Na2S2O3 → Na3[Ag(S2O3)2] + NaBr

The elemental silver will not dissolve. The 2Na2S2O3 will cause a similar blackish patina as silver sulphate, however this is less stable and can be easily removed using a piece of cloth. Generally, all types of horn silver can be treated using this method.

1. Create a solution of distilled water. Use 2 grams (ca one teaspoon) of sodium thiosulphate per 100 ml water. Generally, 100 ml should be enough for a medium sized coin.
2. Warm the solution to a lukewarm temperature (ca. 30-50c).
3. Gently place the coin in the solution. The reaction begins immediately, and is different depending on the type of horn silver:

• Type 1 (black spots) and 3 (waxy layer)
  • Gradually, the coin turns black. This is because of the 2Na2S2O3, which is part of the reaction.
  • In 10-30 minutes, depending on the severity of the horn silver, the horn silver will dissolve.
• Type 2 (metal deposits) and 4 (encrustation):
  • First, the type 2 (metal deposits) and 4 (encrustation) will turn yellow (after 10-20 sec)
  • Second, the silver that is exposed to the sodium thiosulphate will turn darker and black eventually (20 sec until end of procedure)

4. Remove the coin from the solution, using a spoon, and rinse it using tap water. If the horn silver has been dissolved completely, a brief mechanical cleaning of the 2Na2S2O3 can be done using a paste baking soda NaHCO3 with a droplet of water can be used. If the horn silver has not been dissolved, repeat from step 1.

 

@TIF - As always, THANK-YOU.

 

@Roerbakmix - Sir, I thank-you so very much for your response.
I am quite inexperienced in this field, so I will have to read and re-read your response a number of times before I try your advice.
Thank-you, again.
I am presuming that the Baking Soda treatment, in step 4, is to remove the 'black' discoloration from the silver(coin)? Is this correct?

 

Hi @Topcat7. Feel free to PM me, or aks me any questions here.

Sodium thiosulphate and distilled water can be bought fairly cheap: I bought 200g of Sodiumthiosulphate for €2,00 and 1L of distilled water for €1,00.

 

Isn't there a way to create an electrolytic reaction using aluminum foil, sodium carbonate (washing soda) and hot water? I remember using this method one or twice in the past with great success, but I can't remember the details, since most of my experience has been with bronze coins.

 

Yes, but that only works for silver sulphate. This is silver chloride or bromide, or a combination of all above

 

UPDATE!!

(Before and after cleaning.)



@Roerbakmix Thank-you (enormously).


Next coin to try is

 

Wow. Those are pretty spectacular results. Congratulations.
Does the coin look more porous now than before you cleaned it? It looks like it in the photos, but I can't tell if that's just from a difference in lighting.

 

WOW! nice. That looks easier than how I normally knock off horn-silver or bad patinas...

 

@gsimonel

No. The silver (coin) was unaffected by the process. The 'porosity' is down to the photography (totally).

 

@Alegandron
I found the 4 inch angle grinder a bit difficult to use, but now I know how to do it properly, I have a quantity of C4 for sale if anyone wants it? (Lol)

 

LOL, I'm in!

 

Great results, @Topcat7! Happy to have helped. Cleaning horn silver is fun, if you know how to do it. You certainly have a satisfying result. Curious to see how the Sassanid will turn out.

This coin was cleaned with sodium thiosulphate, which is inert to silver and copper. The only caveat is the degradation of the thiosulphate into elemental sulphur, which will add a thin sulphur layer on your coin. This will take a while however (usually occurs after using the same solution for >2h.)

 

Hello,

I am quite new to this forum and read with great interest this topic. I know it dates from 2y ago but I would like to have expert advice on a coin I have and I intend to clean. @Roerbakmix if you have a little bit of time I would greatly appreciate.

best regards

 

Hi: sure, please post some clear pictures and weight.

 

By no means an expert, but I've had a lot of experience cleaning coins of all types.

Silver is pretty sturdy, and I've found that you can subject it to a plethora of harsh chemicals with only minor impact to coin fabric and surfaces.

This Trajan drachm I subjected it to a veritable gauntlet of chemicals:
sodium hydroxide, acetic acid, citric acid, sodium thiosulfate, and at one point I even splashed some gosh-darn Tarn-X on it.



The only downside here is the artificial toning which cropped up; it's started to darken over the past few months. But, I see just extremely minor surface porosity, that barely even registers.

 

@Topcat7, since this thread has been revived, can you give us an update? How did this coin turn out? How is your guide coming along? Is it available yet?