These beads are seen occasionally from W. Africa. The patterns are burnt-in--and such work could easily be accomplished with a hobbyist wood-burning tool (popular in the 1950s and '60s in the U.S.).

In the 1970s, I dyed phenolic plastic beads various colors and then carved through the dyed exterior to reveal the interior yellow colors. I also just carved a (superficially) red bead, then baked it. The red turned black, and the pale yellow turned red.

It's not uncommon for phenolic beads to have burned spots on them that most likely resulted from someone performing a heating test. Marks are often black, outlined in red. (These beads can be baked or fried, to be made to turn red entirely.) My assumption has been that the appearance of tested beads may have suggested doing this on-purpose, to create patterns.

Jamey