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I'm not against the idea, but I was able to break away a lump of the interior timber with thumb pressure, it just won't be possible to work it. The narrow section without fissures should make a couple of thumbsticks. I'm with you on the choice of timber visually, but would need to check the strength (hornbeam would be fine), besides, I haven't got any! What I have just been given is some Macassar Ebony just wide enough to make thumbsticks.
Would look amazing with some rippled maple or sycamore too (edit: or hornbeam)
Can I assume you are against filling the fissures with epoxy (black or clear, not copper or neon)?