ceramic abrasive for about one hour, and the white surface turned into a very bright but whiter than normal silver color.
What did I do to these charms, and are they still OK to use?
Congratulations, you’ve just Depletion-Gilded your silver pieces. 
Or whatever the equivalent term is for silver.
Leaving the pieces in the pickle for that long removed all the
non-silver material on the outer layer, and then polishing it made it
shiny. So now on the outer layer is a very thin layer of fine
silver, which is why it looked brighter white than sterling (just
like depletion-gilding gold makes the surface look like 24k).
So, don’t worry, the charms should still be fine and can still be
marked sterling. 
–Marcy