Zymöl 'Bridge' is a hard carnuba wax primarily marketed for orchestral instruments. I have used it on an ebony fretless fingerboard and liked the result. This might be a nice 'final surface' treatment after the initial smoothing is done.
In my case, and I expect most others, it darkened the wood a bit. Try it on a sample before committing to the real fretboard. You warm it to liquid with your fingers (a little at a time) and rub it into the wood, then polish away any excess before it hardens fully.
__________________Club Hartke - #337 | Steinberger Synapse Clubb - #8 | Fretless - #886 | Darkglass - #77This old man, he plays 6...