I have had promising results developing colour print film in standard black & white chemicals. Not only is it identical to processing black & white film but the fine grain and wide exposure latitude of C41 colour film is preserved in a black & white negative.
35mm colour print film can still be obtained in most city high streets, at least in the UK, and provides an available and low-cost alternative to regular b&w negatives for those willing to process and digitise their film.
I had some out-of-date 35mm C41 colour print film (Kodak GC-400, a cheap, consumer-level ISO400 film, no longer available) and wondered what would happen if I processed it in my normal black & white developer, Rodinal (actually ADOX Adonal, which is identical to the original AGFA formula), so I fired off a roll of the colour film followed by a roll of black & white film at the same ISO400 setting, which I processed in the same chemistry for comparison. I used the same development time for the C41 film as the Massive Dev Chart recommends for Ilford XP2 (a C41 b&w negative film), so if you want to use a different developer go ahead!
The C41 film was given 18 minutes at 20C in Rodinal diluted 1+25, 1 minute stop bath, 5 minutes fix.
Ilford HP5+ was given 6 minutes at 20C in Rodinal diluted 1+25, 1 minute stop bath, 5 minutes fix.
The films were scanned using the same scanner and software (Epson V750 and Vuescan). Vuescan was set to auto-expose and give 2 passes for each frame, which I’ve found significantly reduces noise. The levels were adjusted in Photoshop to give a full tonal range on the histogram but no other manipulation. Samples for comparison are shown below.
Inspection of the films under a loupe showed that the colour negative had low contrast and a long tonal scale together with fine grain; this is consistent with expectations for standard C41 processing. The black & white film showed normal tonal range (it was a dull day when both films were shot) but more distinctive grain. Here are the scans from the 35mm frames. The cropped images are an identically-sized area (10 x 7mm) of the frame:
C41 colour film can be processed in standard black & white chemicals to good effect. Although only one film type has been tested it is reasonable to assume that other C41 films will respond in the same way as they are formulated for standard machine processing.
The wide tonal range and fine grain characteristics associated with colour print film is retained when processed in black & white chemistry, though only a black & white negative is obtained on the orange film base of the C41 film. This is excellent for scanning but is likely to be problematic for anyone wanting to darkroom-print onto gelatine-silver paper.
If you need b&w film urgently or want to use cheap film to give black & white negatives for scanning, C41 colour films like Kodak Color Plus (ISO200), Agfa Vista 400 or any film from the Fuji Superia range (ISO200 to ISO1600) should be a lower-cost alternative to black & white film, especially if you can get short-dated film over the Internet (short-dated colour film should still be fine for black & white work as any colour shifts over time are irrelevant).
If you want gritty grain, well-tested development times for push and pull processing, or the ability to darkroom print from the negative, it would be best to stick with black & white negative film.