I got an emphatic tobacco stain from the prayer beads, and a mild yellowish stain from the round beads. I tried a couple of times in one spot to remove surface dirt on the latter - but didn't press too hard because I didn't want to ruin the surface.
I've attached another couple of images to provide a better look at the surfaces.
Are you finding in your study of phenolic resin, the sort of depth and subsurface detail that these beads seem to have?