Sheet Silver Quality

I sure am glad to see someone else is having this problem! I thought I
was doing something wrong! Generally I use 400 silicon carbid wet, 1000 wet
grey bar and then red rouge, zam or fabuluster. I was still getting pits
on flat sheet, even on unworked sheet. I thought it might be grit from
one of the steps getting embedded in the silver, so I tried skipping
various combinations of steps without improvement.

I seem to have a small supply of this stuff on hand, any clues on how to
use it up other than wire brushing/texturing? How can I tell if the
sheet is bad without working it?
Marlin Cohrs