What finish works best over bone black without smearing it?
A finish with fewer solvents, such as Tried and True oil varnish, works well because it is less likely to attack and smear a previous coat of bone black. Finishes with more solvents, such as Permalyn, can be used too, but they need to be applied lightly rather than rubbed in, since rubbing can dissolve and smear the bone black underneath.