Clean Green Gunk From Scrimshaw Handle

[morestag]

Any advice on how to remove some green tarnish staining from the handle of a scrimshaw? The rest of the knife is mint but there is this one spot of staining because the guy stored it in the sheath. I have tried some mild abrasives (brasso and flitz) and they didn't touch it. Also lightly tried some 0000 steel wool but I think the spot is actually stained and not just on the surface. Any advice is appreciated.