I guess i'm a little surprised re the 'X'. We had done quite a lot of research on nucleus quality including surface smoothness. We disected many pearls that had flaws and could trace many instances back to nuclei surface.
in saying that we also did some tests with bironite and found that nacre covered the bironite nuclei infinitely faster than mussel shell nuclei. We believe that it may have something to do with the surface composition.