Used the closest thing to blackthorn I could find, a piece of wood from a old plum tree I cut down a couple months ago, removed the outer bark, used power saw to shape nob to the rough shape, and then used a black stain with polyurethane, looks good but think I might try some other method in the future.
Then used a sanding drum on my dremel tool too shape the nob.
And then finished the nob with danish oil.