Black and white reversal processing (to make black and white positives) has two additional stages. Following the first developer, the developing action is stopped by an ordinary stop bath, and the film is then bleached to remove the negative image produced by development.
The film then contains a latent positive image in the form of unexposed, undeveloped silver halide. The subsequent steps therefore fog the film, either chemically, or by exposure to light, after which all the remaining silver halide is developed in the second developer.
This allows the silver halide crystals that were not originally exposed in the camera to be developed into a positive image. Finally, the film is fixed, washed and dried conventionally.
The film then contains a latent positive image in the form of unexposed, undeveloped silver halide. The subsequent steps therefore fog the film, either chemically, or by exposure to light, after which all the remaining silver halide is developed in the second developer.
This allows the silver halide crystals that were not originally exposed in the camera to be developed into a positive image. Finally, the film is fixed, washed and dried conventionally.
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