Digital BW, The Print

I have been wondering about the causes too.  It is either the consistency of carbon concentration (or certain dilution not firing the carbon particles consistently through the epson heads), cartridge problems (including air bubbles/improperly primed etc).  A third possibility (though perhaps a bit far fetched) would be the epson printer being 'aware' that the cartridges are not genuine and slightly sabotaging the ink firing.  although my MIS ink say "epson genuine ink" in the epson driver, I believe that epson would keep the info to themselves if they figured a way to identify 3rd party chipped cartridges.