dt, with the solution I use it can. I finished a barrel awhile back and when I had it finished and oiled I noticed a very small thin spot in the blueing. I stewed over it for a couple of days wondering what to do. Finally I just degreased the barrels, fired up the boiling tank and added more coats of rust (Mark Lee) until the spot was deep like the rest of the barrel.
Now with the slow rusting process I'm not sure but once the barrels are degreased I would suspect you might be able to continue the process. The blueing on there is rust and adding more solution on top should start the process up again.
Not a real answer to your question but just my thoughts on it.
