I have done something wrong ?

[Auggieclown]

Hi

I had a copper coin (I think that is an Constantius II ) covered with dirt. I soaked the coin in demineralized water for 1 week (daily change of water) brushed wit a soft brass brush and then soaked in olive oil for 1 week.

See the results please 

I have attached an detail also.

Photos are taken with an use microsope bought from wiki gadgets.



Thanks again for your help

Alec

[Johnny]

looks like the coin was eaten away by corrosion long before you got it

The soaks would, more than likely,  not have damaged it to that point. The only thing is the brass brush,  even soft ones  can remove the patina,

 but as I said,  in this case it looks like the coin  was severely corroded before you got it. 

[Rich Beale]

Indeed, there was never any hope for this one. Nevertheless, you should NEVER use a brass brush. You'll destroy any patina on your coin.

[Arminius]

Probably your coin was covered by a very soft oxidation ( but not patina) layer. These surfaces must be stabilized by wax or resins before careful mechanical cleaning attempts may start. But not by any metal brush.

A brass bruch may be useful for soft dirt on a hard patina or metal surface. But you have to observe the progress or damage constantly.

[Auggieclown]

Good lesson for me !

Thanks !

[Joe Sermarini]

I use brass brushes (specifically the Nic-a-brush type I sell).  As with every other tool and approach to cleaning, you have to use them with care.

[gavignano]

I bought some nic-a-brushes here and do use them. They can nicely remove multiple layers of dirt, if done carefully. I use them under running water (true, some purists not only don't soak in tap water, but won't rinse either). I would say never use a steel brush, even on concreties.

[areich]

I once, out of frustration with my cleaning successes in general attacked a nicely patinated slug with a bruss brush (the one Joe sells) and ended up with a (still nicely patinated!) Hostilian from Viminacium. I never found another coin to try that particular trick on though.