Old Ilford Film
A few years ago I received this box of 5x7 film from a man I bought a camera from, but I never could figure out what kind of film it was. Since it says Ilford on the box ai thought maybesomeone here would know what it is or how old it is?
If you search APUG, you'll find a few posts about using Ilford Line film. I have some data for N.25 and N.30, and the speed is quoted at ASA Weston 3 in daylight. ASA Weston 0.8 for tungsten light - ASA Weston 3 converts to ASA DIN 6.
Develop for 3.25min in ID11 or 4min in Microphen (N5.30 & N.30 film/plates) - If nothing else, it gives you a starting point for N5.50.
As for "how old", it probably dates to the 1950s, early 1960s.
Please, please don't quote me on this but from the information I could find it appears to be an Orthochromatic copy film, rated at an ASA of 6 ("New" ASA Scale) that was sold in the 60s and 70s (though this is at the newest mid 60s due to the lack of the 'sunburst' Ilford logo)
I used a lot of Line film in the 1970's & 80's it's used for copying graphics, it's high contrast and can be used for masks etc. I processed it in PQ Universal or Lith dev (Kodak D85). It's not designed for continuous tone work.
As I recollect the N indicates blue sensitivity and the numbers are for base thickness (.005") and contrast (high). Processed in a strongly alkaline hydroquinone developer it delivered very high contrast.