Cleaning up copper after torch firing Enamel...

I'm torch firing enamel powders, frits, Diachroic, etc. on 24 oz
copper sheets..  I want to retain some of the natural copper color in
some areas of the pieces after being torched (no underglaze..), so I
need to remove the firescale.

Mostly, I've been using SPAREX #2 and a dremel (with an arsenal of
bits, discs, etc...) and the results have been pretty good but I have
noticed some 'dulling' after cleaning where the end of the glass meets
copper.  I want to try and avoid this in future pieces and was
wondering if anyone has a better method of removing the firescale....
( I'm  pretty sure the Dremel is causing the 'dulling')....

I read somewhere that "Penny Weight" cleaner is supposed to work
really well with enamel's, metals and is less caustic but I've never
tried it....  Is it any good ?

Also, should I stay away from the dremel for this application ?
Would doing it the 'old fa****oned way' ( by hand..) be a better
option ?  What would be the recommended sanding grit's / stones etc...
for fini****ng the enameled / fused piece ?   The finest grit I
currently have is wet sanding paper @[EMAIL PROTECTED]
 600 and 800 grit which I use to
give the copper some 'tooth' to hold the enamel previous to torching.

Any suggestions as to the 'above' would be helpful !

Cheers,

/FC