Basically, every fountain-pen ink from established manufacturers like Pelikan, Montblanc, Lamy or Sheaffer is suitable; exotic US inks should be avoided, since these are partly aggressive. Important is that the ink does not dry out in the fountain pen: rinse with water before longer breaks. Water-soluble inks are the safest, while document-proof or strongly pigmented inks can form deposits, eat into the material and discolour it. Since the 342 is not a high-priced model, a moderate risk with a dark-blue ink (e.g. Pelikan Sapphire) can be taken — regular rinsing is then particularly important.