My friend accidentally did it, and got very interesting pictures with an aspect that reminds something akin to pictorialism. I would like to know more about the actual chemical 'impact', what actually happens in technical terms when using developing techniques for color film when having an actual b&w film. I think my friend accidentally used a B&W 35mm film (ISO/ASA 100 or 200) and apparently use the same for the camera ISO/ASA.
Developing black-and-white film as color (C41 or E6) is usually expected to produce blank negatives because the bleach step removes the silver and leaves behind only dye. Black-and-white film has no dye to leave behind.
A partial bleach might leave a faded looking image. Skipped bleach might look like normal black-and-white processing. (These are guesses because I haven't done any partial/skipped bleach processing on either color or black-and-white film.)
A different color process might produce different results, but this scenario is unlikely because they are not in common use.
Cross processing C41 black-and-white in E6 might produce unusual results. C41 black-and-white film does have dye in it.
tfb notes that the temperatures for color processes are much higher than black and white. This might cause "smeary horribleness / reticulation". Normally, such problems occur when there is significant temperature variation among the solutions.
Developing a Black & White film as colour film will leave a dye image rather than a metallic silver one. The secret is in how colour coupling works on a silver image. In effect, you are going to produce a "stain" image similar to "pyrogallol"/"Pyrocatechin" developed images
- The first developer works to provide the negative silver image.
- Stop development at the appropriate time with stop bath.
- Bleach the existing negative metallic silver image which will make it water soluble.
- Expose the film to light or chemical fog to render the remaining undeveloped silver image (which is positive).
- Re-develop the re-exposed image in colour developer (one with colour couplers) to completion. You have already removed the negative image. At this point, you are developing all the remaining silver that has not been bleached.
- Fix to remove all the remaining silver leaving the dye image that was coupled to the silver in the second (colour) development.
- Stabilize with "stabilizer" (whatever that is and does)
- Wash and dry.
- Admire your unique and beautiful work.
Have fun. Good luck.