One of the oldest sources on the subject of carved bone/ivory is
Theophilus' On Divers Arts, which dates to the 12th century. His
suggestion is walnut oil. I suspect that any light oil like that or
peanut oil, etc. would work; apply lightly and wipe off the excess.
On many of my own bone carvings, I've used a mixture of pure
neatsfoot oil and beeswax mixed to the consistency of a hard paste,
I don't know how it will work on something old and already starting
to break down, but it works well for me. There''s also one of the
wax concoctions like Museum/Renaissance/Butcher's wax, which are
used for preserving exhibited items.
Ron Charlotte -- Gainesville, FL
@Ron_Charlotte1 OR email@example.com