This carbonized bamboo knob, from a Cali Bamboo ™ “fossilized woven strand” floor sample, and finished with superglue, has some iridescence in the caramel-colored streaks. Although hard to see in this image, the end grain is mottled dark brown, with the fiber ends looking something water in a like a boiling pot.
The material is fibrous and chips easily, but also polishes well. It does make fine cuts easily, but it looks like filing might work better than cutting to avoid chipping. Cutting without a lathe tailpiece allows high-frequency chatter at the end away from the lathe headstock. But since the plank was only about 0.544″ (14 mm) at the thinnest part, The tailpiece punched through into the cavity for the pot shaft. A plank 5/8″ or 0.625″ thick works better.