Fountains have a love affair with "rag" paper. With bond or copier paper, a special "touch" is needed. Also, using fountains with copier paper requires delligence to avoid the dreaded "blue palm" as the nicely flowing fountain inks dry pretty slowly on "slick" paper.
Interestingly, as writers moved more to ballpoints, the high quality "rag" paper started disappearing from the market.
ALL OF THAT ASIDE, I love seeing a beautiful handwriting done with a quality fountain. PRPrincess and IndyPenDance_Mrs are two of the finest examples I've seen. And, yes, they can make fountain writing beautiful on slick paper. Unfortunately, when I do it, it looks like a NASCAR pileup.