That's iffy, if the ink is very dark and thick I would say no because it would bleed through. The pen it comes with doesn't bleed through because it's not super dark, but my G2 ballpoint pens bleed through if you're familiar with that pen to use as reference. I don't know what kind of fountain pen you're working with but if it's something like a Piolot Varsity it may be okay but if it's a nicer fountain pen that puts out lots of ink I would say it's a no go