Removing Verdigris From Copper

[Jonola (Jon)]

The green spots found on some copper coins are called verdigris this is a copper salt like rust. It is usually copper acetate, but can be a copper hydroxide. Neither of these would come off with any kind of oil. The copper salts will flake off with just rubbing - and that is likely why some people think olive oil, or cooking oil will remove it. In fact it's just the mechanical friction of rubbing that causes it to come off. I have heard that the juice of a peach will remove it but I have never tried it.

Some forms are soluble in water so it might be possible to use hot water and rub them with your thumb or very lightly with a toothbrush to remove some of the material. If that does not work the only other option is an acid dip. Chances are the coins are pitted from the corrosion and removing the verdigris will expose the pits and they may look worse after dipping than before. You will more likely scratch or damage the coin unless you are very careful while doing this.

The acid dip can be made easily from salt and ammonia mixed together. If you do this be very careful and use gloves.  Dip the coin for a short period then rinse and wipe clean.

I wouldn’t undertake this job lightly.  You could first try it on inexpensive coins until you have got it right and then progress to the more expensive ones.  My recommendation is if you can put up with it the way it is then that is the best option.

[Jonola (Jon)]

Another method if you are feeling brave with the chemicals

After careful manual cleaning and drying at room temperature,  soak for
a couple of days in a solution of benzotriazole in industrial methylated
spirit, and then lacquer with incralac. I have seen packs of these
available on the net.
Silver doesnt need lacquering; if very tarnished,  clean
electrolytically by wrapping in aluminium foil and immersing in a sodium
carbonate (or hydroxide) solution. Use dilute, and try on cheap coins
first and check every few minutes.

[hedgehog]

Good one Jon, it's always hard to clean the copper properly. Just one thing to add with the silver , it will buff up very nicely with a soft dry cloth afterwards.

[coleggwent(phil)]

i will say jon why pay the cost of sodium when the best result is warm water every time like you say wrap your coin up in foil hold it under the hot tap just to warm it up  wait for it to fizz up when it stop just take the foil off and wash it under the tap same thing without the cost 

[Jonola (Jon)]

Hi Phil

Silver sulphide (The tarnish on silver coins) is the least soluble in water of all the silver compounds. However, it can be readily reduced by contact with aluminium in dilute sodium carbonate (Na2 CO3) solution, the reduction resulting from the liberation of hydrogen. As sodium carbonate is the salt of a strong base and a weak acid it dissociates to give an alkaline solution.

I think it is about £3 a pound and that will last for hundreds if not thousands of coins. You are right that the method you use works well. I suppose that it depends how much time and effort you think the coin is worth really.

[Stig(The)]

Interesting & informative thread Jon,thanks.