"newshound" wrote in message
...

Ed's right , you have etched the zinc out of the surface.

If you are lucky and it is not too deep, you can use a hydrogen peroxide
pickle technique to strip back the copper rich surface.

http://www.artmetal.com/files/import...onfe/H2O2.html

It will leave the surface dull, but well within the range of hand
polishing. 4 gal is a lot of peroxide though.

It is also a great technique for cleaning up when you burn out the zinc
with a torch after silver brazing or etching it out with acid flux.

HCl is a little strong for general cleaning. I prefer citric acid or
sodium bisulfate (AKA Sparex, or sold in the pool supply section under
various brand names as a granular ph reducer for pool water).

Paul K. Dickman

Good link! Sadly hydrogen peroxide is not so easy to come by this side of
the pond thanks to the activities of a few of our eastward facing citizens

The mix uses only 3% solution. Over here, that strength is sold at drug
stores as a topical antiseptic.

Paul K. Dickman