I use Laurel Mtn a lot and as Keith points out if the bbls are warm,,then the copper from the coppersulfate kn the soln 'plates out' for lack of a better term.
Other commercial solns use coppersulfate too I imagine, many of the home brews called for it.
You will also get the same plating w/the L/M if when applying you rub a spot back and forth to apply the soln even ever so gently.
This appears even if the bbls are cold and is a separate occurance from the above warm surface thing.
Once over and that's it. Go slow enough to make sure you cover everything the first pass. Don't worry if there's a small area not covered or one pass slightly misses the one next to it.
It'll cover up in the next cycle.
Scotchbrite any copper plated areas down to bare metal and blend the polish to the original. No need to remove all the rest of the bluing if it looks OK.
Re-coat and keep going. The repaired area will catch up in color within a couple coats.
Throw that piece of Scotchbrite you used to polish that damaged area away. You don't want to use it somewhere and drag copper back onto the surface again.
