Proof of principle: removing iron oxides from silver coins

With the rare exceptions of crazy tooling or nasty stripping of course!

 

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In this case, my opinion is that you spent €8 and some amount on chemicals to improve a coin which was absolutely terrible making it worth little more than €8 considering the eroded surfaces.

The problem here may be that the coin in question was less than 50% silver so we lost a bit of original alloy along with the deposits that needed to go. Certainly the coin was improved in the process but I would suggest it was worth more as an educational experience than as a way of freeing this particular coin. What you learned applied to a very rare coin of the period would most certainly be worth the chemicals and effort. If you just wanted a denarius of Severus Alexander, there are easier answers. Of course finding someone willing to sell a Pertinax etc. for €8 might be difficult but when you do find that coin, you will be ready for it. That is great; thanks for sharing!

Certainly true! All ancient coins have been cleaned. The ones that have an inch of dirt on them previously had at least two inches of dirt. If there is a sin involved in cleaning ancient coins, I might suggest that it is telling people to soak coins in olive oil. Actually that is just one of the sins we see. Somewhere else here on CT today we were shown a Gallienus Provincial that was scrubbed with a sharp pointy object and called 'smoothed'. Every so often we are treated to coins that are electrocuted, tumbled or burned with a torch. Cleaning ancient coins is not a sin but doing so without the slightest idea what you are doing is just a bit sinful and has wrecked quite a few coins in most of our collections. I wish I had the shills of Roerbakmix in particular in the ability to diagnose 'patients' before making them 'vicitms'.

I hope everyone read that line.

 

This is incredible transformation. You are chemist maybe ?

 

It would seem that you'd need an extensive education in chemistry to know all of that! Not to mention, knowledge of just how far you can go in coin cleaning before you ruin something. Kudos to you - the coin looks fabulous!

 

I echo the responses given above: HCl (or any acid) will dissolve not only the deposits, but also the coin. Cleaning silver coins is much easier than bronze, in my opinion, as (especially with coins of high purity), one does not have to worry too much about the effect of the chemicals on the coin itself.

Indeed, this coin served as a proof of principle. I learned at least two things that will save me from experimenting with more valuable coins (both in monetary and historic sense)
1) the chloride of HCl will indeed react with the silver, but only to a limited extend: a thin layer of AgCl (also known as horn silver) forms, covering the entire coin, (which actually is a rather pleasing dull-grey patina).
2) this thin layer, though easily removed with sodium thiosulphate as described above, hinders the removal of the iron deposits: the thin layer that covers the coin will also cover these deposits, protecting them from the acid

With more valuable specimens, especially when most of the coin is just fine apart from some minor deposits, I will use a precision pipette:

I've worked with those handy pipettes during lab internships, and they might be quite useful for this purpose. I'm still looking for a trinoculair low-magnifying microscope (trinocular so I could share real-time video imaging on the forum - will be fun ).

I have some experience in the lab, but mostly biochemical, with focus on the bio and less on the chemical. Coin cleaning is fun and can be rewarding, by increasing the value of the coin and the appeal. It's just another aspect of the hobby I enjoy!