Nope, the seams are not visible to the naked eye (and, of course, cannot be felt). I've only looked at both of these mibs with a 10 power loup (lost my good one), and they're not discernable in the glass at that slight magnification, either. I'll be interested to see whether they can be seen in the glass under Chuck's microscope . . .
They only became visible when I hit both mibs with the black light, and then only in the slight orange florescent "skin" that covers part of each marble.