Hero 234 vs Platinum Carbon Black - resistance against water-brushing

Platinum Carbon Black ink is significantly more resistant than Hero 234 ink against getting pigment dislodged when friction is applied onto re-wetted ink marks.

Dry rubbing (with a paper towel, not my fingertip directly, so as to avoid dampness on my skin) managed to dislodge some pigment from marks made by both of these inks. It looks more noticeable with Platinum Carbon Black ink on this test sheet, but only because the pen used to write with it is wetter and broader than the other pen, and thus put down more ink (and hence more pigment) per surface area covered by the actual marks, despite both pens having Faber-Castell steel EF nibs.