In times past, photographers often wrote on the film edge to identify the shot and provide a reference for cataloging the film. This is still required for some forms of historic HABS preservation photography, which I still do in Texas with large format film. In choosing pens, Schaf Photo helped me — thank you.
The two best permanent archival pens for writing on film base in my experience are the following:
1. STAEDTLER pigment liner (I like the 0.3mm for writing on edge of 4x5, but the 0.1mm and 0.5mm are also usable). Good density. Despite their claim that the pen is still usable if uncapped for 18 hrs., I found that it wasuseful for one day of labeling, then lost much density/flow.
2. FABER-CASTELL PITT artist pen. I like the “S” nib size for 4x5. Keeps flowing for several jobs. I always retrace my writing to get more density. Not perfect, but due to the convenience of the one being usable for a longer time, I have returned to this pen as my favorite.
Remember that black ink in a negative will print and scan as white. Therefore, write slowly and if needed, immediately go over each letter and number that you write to make the writing blacker.
I only use the black ink. Only write on the film base, not emulsion. These inks, when dry, are waterproof. If you make a mistake, wipe it off immediately and gently with a damp soft cloth. To not damage the film base. Once dry, a white plastic eraser such as Staedtler or Faber-Castell can be used.
PS: do NOT use a Sharpie it is not archival.
Happy labeling!
Paul
Paul Chaplo MFA, AIA-Assoc.
HABS Photography
Dallas, TX