I believe it is both ! Encrustation with BD attacking the coin. I had a nice sestertius of Caracalla that had some curious blobs of reddish encrustation (mostly on reverse). The primary question was whether to remove or allow to remain. The spots were not that large and I decided to put off a decision. About six months later I examined the coin and much to my alarm the neon green spots had appeared ! Happily they seemed to have a made a 'home' in the spots of oxidized encrustation on the reverse. The decision was quickly made a nd the 'stuff' was removed post haste !
I believe this coin will be saved too. The patina might lose some of its "venerable" look but the alternative is unacceptable !
IN GOD WE TRVST ....... all others pay cash !
COGITO ERGO SPVD
I think ...... therefore I yam