In principle any fountain-pen ink of various makers can be used; one should only watch for 'fountain-pen ink' in the narrower sense and not use document-proof or particularly aggressive inks in sensitive reservoirs. For flexible nibs, especially the Waterman lever pens of models 52 and 54 from the 1920s and 1930s are recommended; they write excellently, but the hard-rubber bodies are UV- and sweat-sensitive and tend to discolour. To source such historical pieces, e.g. Lutz Fiebig in Magdeburg is named. A specialist check before purchase is sensible, since nib condition and sac tightness are decisive.