John:

Ebony can be difficult. If you are using a friction polish or any
finishing method which generates heat, that could make the problem
worse. Heat from aggressive sanding may also contribute to the problem.

Bill

In article ,
says...
Hi all,
Recently started using ebony as inlays in small turned boxes. Problem
is that they develop radial cracks in the process. Any advice to
prevent this would be appreciated.
Thanks,
John