What do you do about crumbly patina?

[user 1769]

Almost invariably pennies and halfpennies that I find, like modern 1 and 2 cent pieces, have a green, crumbly patina that comes off very easily around the edges of the coin, and in areas of high relief. In some coins I can see the patina pretty much crumbling away in front of my eyes as the coin dries off.

Is there a way of handling the coins to preserve this patina intact? Often it contains most, if not all of the coin detail. If I keep the coins wet until I get home, is there a way to fix it in place? What do other members do about crumbly patina in predecimal coppers?

 

[Paulmarr]

I have found that most pennies and half pennies that are found on the beach are severely corroded beneath the green patina and aren't worth cleaning or worrying about. I am sure they have no commercial value other than the .07 cents they are worth for bullion value (penny). I just pop them in the "brown buggers" bag in their green state for my end of year count/display.

I do not think there is a way to clean the coin and retain the detail - but if someone has figured it out I would like to know too.

 

[the duck]

This is a problem as its sometimes called bronze disease and it is very hard to stop and it is contagious so can spread to other coins, in order to fix it you need to take away the air, but mainly its best removed by tumbling with fine garnet pieces in a tumbler which doesn't remove the old green patina that makes some coins look great, but will knock the powdery stuff off the coin, some coins when tumbled just fall to bits this cancer of coins sometimes goes right through them
lanolin will halt it temporarily

 

[user 1769]

Hi the_duck, it's not bronze disease (copper chloride) I'm talking about, but the normal, blackish green patina, probably of sulfides. But maybe I'm just better off leaving them untouched.

 

[user 1769]

This is what I mean: The patina is crumbling around the coin edges and in areas in the middle. It's not (as far as I can tell) bronze disease. Most of the detail seems to be preserved in the patina, as you can see where it's flaked off.

 

[Goldpick]

You could always vacuum seal them in small plastics pockets, that should eliminate most of the air, thus prevent further oxidation of the metals.