Don't use the cartridges that come with the kits, they are pure junk, Tony at the golden Nib sells a bottle of Schneider cartridges that are inexpensive about 7.00 for 30 international cartridges, also don't put a cartridge in until you actually use or sell the pen, otherwise you'll have a gummed up feed or nib, Exotic blanks as well as heritage pens also sell Private Reserve ink which is a good quality ink, all 3 of these dealers are
IAP members and great folks to deal with, also check out DCbluesmans behind the nib series in the library if you are just getting into fountain pens. Lots to learn, but well worth the effort, I carry a bottle of ink with me to shows and just let the customer dip the nib into the ink to try the pen, ON GOOD PAPER, so the pen writes smoothly, not like notebook paper which feels like sandpaper under a decent nib. It would be like taking demonstration ride in a new car down the side of the Grand Canyon.