Amongst my various accumulations I've had this rather mysterious or unidentified countermarked 8 reales for about 40 years now just hoping someday it might be identified. The countermark is very well done with raised letters "J.J." in a scalloped indent.

The host coin was struck in 1800 at the Lima Mint with initials I. J. and appears to be sea salvaged or perhaps grave dug. The black crud on it is impossible to remove as I tried various non-silver cleaners so I'm guessing it is in fact oxidized silver.