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

Thank you very much for your help. Enjoy your holiday

 

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is sodium sesquic

i appreciate it! thanks, joe

 

Not quite sesquicarbonate, as this doesn't have carbonate or bicarbonate. It does have (thio)sulfate, but beyond that my chemistry is not useful lol

 

no worries, you undoubtedly know more than me. Thanks though

 

i just purchased! thanks again

 

I am planning to use the process described by you (@Roerbakmix) in this post and several others. I was going to PM you but thought others might be interested in your response to my question.

I've acquired all of the materials you describe. I would like to clean an edge spot of horn silver on the reverse of this coin: As you can see it is a relatively high grade Roman denarius with otherwise lovely toning. I'm nervous about whether soaking the coin in a sodium thiosulfate solution will impact or change the overall toning of the coin. If so, might I take a minimalist approach and apply sodium thiosulfate with a q-tip to the affected area, repeatedly combining with careful manual cleaning using 'Le Crayon a Andre' tools? Any guidance would be appreciated.

 

@Fugio1, this is a difficult coin to clean. Not because of the encrustation, which will dissolve easily in sodium thiosulphate, but because of the lustrous yellow patina.

Immersing the coin in sodium thiosulphate would definitely affect the toning: the coin will turn dark grey to black. See: https://www.cointalk.com/threads/hieronymus-of-syracuse-restoration-of-a-valuable-coin.365640/
In this thread, I restore a 10 Litra piece of Hieron (which sold for $1100 at CNG, if I remember correctly). The effect on that coin was dramatic (but expected): it turned black entirely. As I've explained in other posts, this black deposition can be removed easily, but the overall aspect of the coin will be different.

Note that this deposition will easily dissolve, as mentioned. I classify this as 'granular with sharp borders':

which is the same deposit as on the coin of Hieron in the beforementioned thread, and also the same as in this thread: https://www.cointalk.com/threads/cleaning-a-sceatta.370033/ (second post):

after:


Back to your coin: how to proceed?

First, if you're totally unexperienced, I would recommend against restoration. Otherwise, I would advice the following steps:
1) prepare a solution of sodium thiosulphate in distilled H2O. Use a strong solution, e.g. 10g in 20 ml of H2O.
2) with a pipette: remove about 5 ml from the solution, and add to 5 ml of glycerol (also known as glycerine). This will increase the surface tension: Without the glycerine, the surface tension will be too low, and the droplet will spread out to on the surface of the coin (see here: https://www.cointalk.com/threads/pl...ochloric-acid-cleaning-my-avatar-coin.383989/ where I encountered a similar problem, but then with 30% HCl)
3) use a mechanical pipette, and place a small droplet of ~500 uL (0.5 ml) on another (silver) coin to test the surface tension. Preferably, you want to create a droplet which will not spread out on the surface of the coin, but that can be 'guided' to stay on top of the deposit. Add more glycerine if needed.
4) if the solution is less than <15 minutes old (sodium thiosulphate will degrade to elemental sulphur, amongst others, causing depositions of sulphur on your coin that are nearly impossible to remove): place the droplet on the deposit of your coin.
5) you will see that the deposit will dissolve easily. If not, use a droplet of acetone to remove any fatty layers that protect the AgCl from the sodium thiosulphate.
6) rinse the coin with water and gently scrub the (now weakened) deposit with your thumb.
7) repeat until finished (remember step 4 though!)

I would advice against mechanical cleaning unless you really know what you're doing.

 

For all those interested in the beforementioned guide: I've added the 2019 version (which hasn't been updated since) to ResearchGate:
https://www.researchgate.net/project/Ancient-coin-restoration

 

Is this true only of silver, or bronze as well?

 

@Roerbakmix, I'm grateful for your response. Although I have some experience mechanically restoring low value coins, I have no experience with chemical restoration. So I'll take your advice and not attempt to do this myself, at least not at this point. I may have it professionally done in the future.

 

I do not entirely agree with this statement: as mentioned in my post above, sodium thiosulphate will degrade (usually after about 15 minutes, depending on the concentration of the solution) into elemental sulphur (amongst others).

This will result in a thin layer of elemental sulphur on the coin:


Though in the end the deposits dissolved, I had to resort to abrasive methods to remove the thin layer of sulphur. In the end, the result was somewhat pleasing:

 

No problem. It is a difficult to clean coin if you want the original patina to remain. Otherwise, it's extremely simple.

If you live somewhere nearby (the Netherlands), I would be happy to clean the coin.

 

Well, I revise my statement. It won't cause major damage to the coin, but could cause some very minor surface roughness as a result of loss of the original patina.

The below coin is "billon" or a rather low silver content coin with mostly bronze.

I left this coin in sodium thiosulfate for about 5 days straight. Despite what chemistry and others have said, I have found thiosulfate to be highly effective against red/orange iron oxide rust.


None of the detail was lost, although it did remove some of the patina - hence a very mild case of surface roughness.

Nothing that Renaissance wax can't save.

So, basically, you are likely to lose some original patina, depending on the circumstance. Only you can decide if its worth it or not.