Good point, Charles. It's been a long time since I've retouched a negative. Yes, the "tooth" for pencil retouching is on the back side. Is dye retouching for b&W not done on the emulsion side? Hard to remember since the last time I did it was 15 years ago.

Some B&W films are very reflective/shiny on the emulsion side. Tri-X is less so than other films, which is why I've not had problems in "can" type pinhole cameras. I think Bergger 200 also has a fairly matte emulsion surface. I ran into trouble with Fujichrome Astia reflecting light onto itself in a "can" camera.

Peter Gomena