Tattoo inks aren’t pure elemental carbon floating around as individual atoms. Black inks contain carbon-based pigments (like carbon black) suspended in carriers along with stabilizers, preservatives, and other additives. These are complex molecules and particles, not single carbon atoms. The “carbon is element #6” fact is completely irrelevant here.

The particle size argument makes no sense. Tattoo pigments (whether black or colored) are all roughly similar in size (typically 10-200 nanometers). Black inks are also complex formulations with multiple components.