I’ve been meaning to do black and white slides for a while now, but I’ve always found it too much of a hassle to perform. Recently, I’ve become intrigued with the idea of shooting and hand-processing 16mm video on a vintage camera (which I got over eBay for less than 20 bucks). Of course, the process for both still and movie film are the same, so I decided to do a first trial with a roll of HP5 plus that I had shot with my Argus C3. The camera was opened up once while the film was still in there, so there may be some complications to the results.
Principles of Reversal Process
The principles of the reversal process is fairly simple. First, a negative is developed normally. The resulting silver is then removed using a bleach step, resulting in an emulsion with regions of lower silver/halide content where there had been higher negative density. Finally, the emulsion is re-exposed and re-developed, giving and inverted image to the original negative – i.e. a positive image. The actual steps are fairly simple. However, it is a huge challenge to fine-tune each step.
The first development is arguably the most important step, since it determines how the latent image is processed, and can exercise the greatest control over the final image contrast and dynamic range. For my initial tests, I used the Ilford Multigrade paper developer (I haven’t actually seen anyone specifically recommending Ilford MG, which may explain the results). This was supplemented with sodium thiosulfate, which acts as a halide solvent. I have read that fine-grain development is unnecessary at this step since the developed image will be removed in the bleach step, though I have not tested this claim myself.
For the bleach step, I use a permanganate bleach (Potassium permanganate + sulfuric acid). After the bleach step, the film can (and in most cases, must) be exposed to light. At this point, the film appeared to have an image that is creamy in some spots and dark on others. There is a yellow stain on the emulsion, which has been attributed to the staining by permanganate. Typically, there will be a clearing step (to remove said yellow stain) followed by a fogging and redevelopment (to fully expose the remaining halide, and yield the positive image). However, I read somewhere that a toilet cleaner called Iron-Out can be used as a fogging developer, essentially combining the fogging and second development steps. Because it is a chemical process, it makes it much faster and homogeneous. After consulting the material safety datasheet (MSDS) of Iron-Out, I realized that it contains sodium metabisulfite, the chemical commonly used for clearing permanganate bleaches. I then decided to perform all three steps (i.e. clear, fog and redevelop) by inspection. The results are as follows:
I have to re-iterate that the film back had been accidentally opened on this roll of film so severe fogging is expected. The results show that, although there are some positive images on these frames, there was also a strange fogging of the highlights. In fact, in some areas you can see the image transition from positive to negative. This may be due to
- Insufficient bleaching – permanganate bleach has a tendency to cause emulsion lift-off. As a result, I am using a low-ish bleach concentration and duration.
- Insufficient first development – developer does not convert sufficient amount of halide into silver, and the residual halide gets developed at the last step. This has the effect of cutting off the highlights.
- Insufficient halide solvent in first developer – similar to #2, this also helps to explain the general muddiness of the tones.
I decided, at this point, that perhaps the first developer used is simply unsuitable for reversal processing. I then moved to Dektol as my developer of choice.