How can I cure my ugly looking 5kop1788SPM ?

[sigistenz]

Hi friends, I did not like the uneven color of my 5kop1788SPM. I put it for about 10 minutes in hot soap suds with a good dash of ammonia solution.

The contrasts got even worse, the black deposit cannot be brushed off with natural or nylon bristles.

What can I do to restore the otherwise nice overstrike coin? Thank you for your help. Sigi

[bobh]

Hi friends, I did not like the uneven color of my 5kop1788SPM. I put it for about 10 minutes in hot soap suds with a good dash of ammonia solution.

The contrasts got even worse, the black deposit cannot be brushed off with natural or nylon bristles.

What can I do to restore the otherwise nice overstrike coin? Thank you for your help. Sigi

In general, I would not clean any copper coins because it never works satisfactorily. The only exception would be in case of verdigris which sometimes comes off after soaking the coin in olive oil for a month or two. Did you try olive oil yet?

 

Since you have already gone this far, though, I would try using pure medicinal acetone which you can get at your local Apotheke in small quantities. There are some caveats regarding the use of acetone, though:

 

(1) Acetone is EXTREMELY FLAMMABLE! So do this outside, or else be very careful with it.

(2) Acetone has been shown to react unfavorably with copper under the presence of water and light. Therefore, the coin should be very dry and should not be exposed to light when this is done. Also, since acetone evaporates very quickly, there is no need to rinse with water after you are done. In fact, this could make it worse for the reasons stated.

(3) If you don't see any results after about 10 minutes, I would stop (i.e. don't soak the coin overnight). Let the coin dry normally; acetone evaporates very quickly, so there is no need to wipe it or anything. When I use acetone, I usually save a little glass jar which usually has some kind of rubber seal on the lid. You need a lid to close the jar because acetone evaporates very quickly, but the material used in the seal can also react with the acetone vapors! So it is a good idea not to do this for too long a time.

 

I think acetone might help because the black area might be some organic compound such as tar. However, it still might not turn out like you wish because who knows how deep the black area goes?? Also, it was probably improperly cleaned sometime in the past, so you never know what substances have reacted with the copper and existing patina to produce such a stain.

 

I once had this problem with a small U.S. copper 2 cent piece which had been artificially toned and had a blotchy area on it. As a last resort, I stripped off all the patina with a combination of vinegar and salt. However, it still didn't completely get rid of the stain which turned black similar to the one on your coin. So I let it soak some more in the vinegar. Then I rinsed it well and put it away in a paper envelope, hoping that in a year or two it will retone naturally and perhaps it won't be as obvious. But as far as i am concerned, that coin couldn't have been made any worse than it was, so I felt that the cleaning was justified.

 

Good luck -- hope you don't ruin the coin like this!

[squirrel]

Hi Sigi!

I have tried in the past to remove the green verdegris using ammonia, which does dissolve the copper salts, but the verdigris seems to etch and corrode the surface, so that once removed, you have the black areas you show. The ammonia will also very nicely remove any brown patina, so that is not always the best method. You can try longer soaking in ammonia, but better to work the dark areas with a cotton swab dipped in ammonia, and keep changing to a clean swab. Otherwise You would need to somehow mechanicaly (ie abrasive, bronze bristle, etc)) remove the black layer, until you hit shiny copper, and of course you loose detail, because the corrosion is into the metal quite deep. I dont know of a way of actually leaving the black spots, and chemicaly lightening the color back to a nice brown.

 

Whatever you do.. stay away from acid of any kind... or you will pit and etch the copper even worse. Good luck!

[squirrel]

One other thought.. has anyone tried to copper plate over the black area, to restore a new layer of copper, so that it could re-patina to match?

[sigistenz]

Thank you Bob! I really appreciate your detailed reply. As the black stains are not tar or the like - but definitely some kind of corrosion, I do not expect too much from acetone.

I will however try it. Vinegar and salt sounds interesting, I'll try it with a similar coin (of no value). I've read that acid consumes copper, but I think the stains must go somehow

in order to obtain an equal overall coloring, which then hopefully darkens (or can be made darken) equally. Would there be any other suggestions / experiences ? Sigi

[sigistenz]

One other thought.. has anyone tried to copper plate over the black area, to restore a new layer of copper, so that it could re-patina to match?

Thank you Josh! I think I am now cured from using ammonia, as it eats copper as you say. Someone advised to try a "buffered EDTA solution" but does not give any details. I find it difficult to obtain EDTA in a small quantity and have no idea as to buffering it. Copper plating this coin is an interesting idea, but copper would probably not cover this corrosion (?). Would there be other suggestions? Thanks again, Sigi

[squirrel]

Another nasty but obtainable chemical to experiment with would be Ferric Chloride. You use it to make printed circuit boards. I did this when i was a kid, making radios and such. You draw with a waterprooof pen on a circuit board that has a thin layer of copper. where you want your layout, then soak it in Ferric chloride for 20 minutes, and it would etch away the copper except where the lines of the pen were. leaving the circuit traces. Available at your local radio shack store. Might be worth a try on some scrap coins with corrosion.

 

You could always spray paint the whole coin brown.