Just a tip to pass along, in case anyone else has the same use-case and question. I haven’t seen it mentioned elsewhere here. I keep notes about books in individual composition notebooks on my shelf (in my case, books of the Bible). For labeling them on the spine, I’ve had a good experience with these pens:

- For tape-based spines, Sharpie’s white oil-based paint marker

- For paper or fabric-based spines (Clairefontaine, Rhodia, Mead, Wexford), I’ve used Artline’s Marker for Fabric, in white.

If anyone else has other suggestions, please chime in!

Jed