Finish for Coolibah Burl

Greetings all - would there be some kind person in the forum who can help me by advising what sort of finish I can put on a piece of Collibah Burl? A friend was given the burl and he sliced it to make pen blanks sharing it with me and another mate - three ways. I was given several pieces and ended up with one piece flat on two sides and the outer burl on the third side - it measures about 20cm long x 12 cms high and tapering away each side. I intend mounting a small insert clock in the broadest part. What finish can I use on the two sanded faces and what should I use on the rough original outer (back) surface?