The fact sheet for Ilford Plates type N.50 Thin Film Half Tone, N.50M Thin Film Half Tone Matt, N.50S Thin Film Half Tone Stripping, N.40 Process, N.40M Process Matt, N.40S Process Stripping, G.50 Ortho, R.52 High Contrast Thin Film, and R.40 Rapid Process Panchromatic. Recommendations are given for filtration, for developer and fixer combinations, developing times, etc.
These plates are pretty slow – around the speed of photographic paper. I shoot them around ISO 1, normally after testing one or two from any given box. The slow speed is actually an asset at this point because it means they have less grain and have likely survived better than faster emulsions.
I can say from personal experience that the N.40 Process Plates can be used also for conventional photography under normal lighting. I stand develop them using Rodinal or HC 110, very dilute, for around an hour. Acetic acid stop bath, regular film strength fixer, etc. The emulsion can sometimes peel off the plate if they spend too much time in solution, or if they move around too much in the developing tank. I often use a Combi-Plan tank for these, and it’s great except sometimes they shift around in the rack and it can damage the emulsion. You can use a rubber band to prevent this. Different plates even of the same type have done this to differing degrees for me in past. It’s not consistent. Ilford ceased production of this type of photographic plates in the mid-70’s, and by this time, who knows what they’ve gone through before you even expose them.
Please note – I do not own the rights to these documents. If you are the rights holder and you want me to take them down, please contact me and I will do so without objection. My aim here is only to make available for public use information which is otherwise unavailable or hard to find. I do not seek to profit from this in any way whatsoever. This information is quite old and hard to find, so I’m only trying to help others out.