Cleaning crust from copper

[Stegner]

Found a thimble at an old hotel site. After some cursory cleaning, I realized it is copper. The advice I got on this was to use salt/vinegar and/or lemon juice, and to work a brass brush on the tough spots.
I now have gotten this thimble looking much better but there are some real stubborn areas - at the top the encrustation is tough - like concrete - what suggestions do you have for me to finish this job? Or should I leave well enough alone? I was hoping to clean this and mount it for the now-owner of the property, and this doesn't seem to be good enough yet for that kind of presentation. Any advice?

 

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[Stegner]

Any advice?

 

[ResurrectedVirginia]

I don't know. I'm in the same boat as you.

 

[ResurrectedVirginia]

I don't know. I'm in the same boat as you. electrolysis maybe. I haven't tried any non ferrous electrolysis though so I cant promise anything.

 

[lastleg]

I've had success removing "concrete-like" encrustations with original GO-JO and a rotary tool.
Start with the fiber attachment and if that doesn't work go to the brass wheel attachment. You
will need to put some preservative on those spots to keep them from coming back. Lowes has
the necessary rotary attachments.