Ivory :? Sounds insane.
The oldtimers generally were good at finding cheap local substitutes for imported materials. Further back in time when cash was even scarcer and transports even more expensive I assume that craftsmen were even better at finding creative low budget solutions.
So.... Why would a super expensive high prestige material like ivory end up in a plane? Woodworkers and blacksmiths alike have until recently been good at finding cheap solutions when making their own tools.......
This leads me to the assumption that there must have been gentleman woodworkers in Roman times. This plane being made with the purpose of showing that the owner was a GENTLEMAN woodworker and not any ordinary country craftsman.
Just my thoughts.... and I am neither historician nor archeologist.
This leads me nowhere. :?