Soaking copper in olive oil ... Will it effect lustre?

[Old Copper Nose 0]

Hi,

I am hoping to get some advice from fellow forum members who have tried to treat the dreaded verdigris on copper coins.

I have a Victorian copper penny which is practically uncirculated with a great deal of mint lustre. The obverse has been struck from a rusty die and has some pitting and what seems to be the onset of some verdigris spots. The reverse of the coin is problem free and has great eye appeal.

I have read about different ways of trying to remove the verdigris, but I'm so nervous about trying anything myself as I don't want to cause further damage to a coin that cost me a couple of hundred quid.

I guess my question is to those of you who have immersed a coin in olive oil for an extended period of time. If I was to do this am I in danger of ruining the lustre which is on the coin? There are some issues with the obverse but the reverse of the coin is damn near perfect … I don't want the coin to deteriorate any further!

Many thanks,

J.

[Peter 615]

My experiences with using olive oil on coins is on Romans only where a certain amount of cleaning is accepted.I

have disposed of coins with differing grades/problems of reverse/obverse.

Sometimes if you can't live with a coin you have to bite the bullet

There maybe a accetate remedy but this will still leave the scars.

[TomGoodheart 403]

The only coins I've ever done this to were a 19th century French cent found on the beach and a penny picked up in change that I thought had verd but seemed to have been painted green (!)

While the oil cleaned both, the French coin came up quite pink. I imagine that the mild acidity of the oil gradually disolves away the dirt, but also imagine that if it can eat into verdegris, it will effect the surface of the coin. There's no way as far as I know to make the treatment specific to one part and not another.

Patina, lustre, whatever are all surface effects. I can't see that anything that will touch verd (as opposed to simply washing it loose) won't also effect that outer layer of oxidation on a coin, which is of course what gives it its appearance.

Over the years I've tried a few different ways to change the appearance of coins, from cleaning to trying to accelerate the oxidation process to take the overly shiny edge off a 'museum cleaned' silver coin. None have been 100% succesful I'm afraid. The few spots of verdegris (on valuble silver coins) I have accepted I'm just going to have to leave alone.

[Red Riley 2]

I think you will have to treat the spots of verdigris rather than the entire coin. A little while go I posted this;

OK, here's my way of treating a toned copper coin coin with a verdigris hole appearing;

1) Carefully scour the hole with a needle to remove as much verdigris as possible;

2) Carefully wash coin;

3) Soak end of cocktail stick in ammonia for 15-20 mins;

4) Very carefully knock off all drips from cocktail stick;

5) Even more carefully insert stick into hole and twist around. What you are trying to avoid here is getting any ammonia on the undamaged surface of the coin;

6) Make up a paste of sulphur and vaseline. You only need a tiny quantity;

7) Take another needle and put a tiny amount of the paste in the hole;

8) Leave for a while. The longer it is left, the darker the area treated with the paste will become, so it is possible to some degree match with the colour of the coin;

9) Wash coin again;

10) Bob's your uncle, Fanny's your aunt!

Obviously you will not need to tone the coins, so miss out 6) to 8).

As regards silver, I soaked a 50% silver 6d in amonia to remove the green spots and the result was very successful, just small spots of grey where the verdigris had been.

As ever, given in good faith and no responsibility accepted!

[Peckris 579]

I'm afraid if the coin has "a great deal of mint lustre", then there isn't much you can do. Having said that, olive oil is the least invasive thing you can do, but you should monitor it regularly and pull it out at the first sign of any deterioration.

If it didn't have lustre, my advice would have been : leave overnight in blasamic vinegar. This will lighten the whole tone of the coin quite a lot, apart from the verdigris patches which will be converted to darker patches with the green all gone. The coin can then be washed carefully, dried, and thinly coated with olive oil as a finishing touch (you wipe off most of the oil leaving only a lustrous sheen). If you can live with the lightening, this is an effective way of dealing with green. Needless to say, practise your technique on a low value coin!