How can negative film or paper be processed to produce a positive image?
Asked 9/5/2018
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I’ve read that ordinary negative film or even some negative photographic paper can, in theory, be turned into a positive by changing the processing steps. What changes are made to the normal development process, and what kind of result does this produce on film or paper?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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The original negative was created by exposing a light-sensitive emulsion. The grains within that emulsion are brought out by the intensity of light that hit them along with the development process.
What you have is an image where the more intense light is captured as a darker area on the negative and the less intense as lighter, thus, the negative.
The key here is that the lighter parts of your negative have had less exposure. So, to reverse the negative into a positive, one needs to bleach away the developed grains (causing them to go from dark, to light), re-expose the negative (causing the light spots to gain further exposure), and re-develop (allowing the light areas to now darken).
At the end of this process, you'll have a positive. To recap:
- Develop your negative
- Bleach the neg
- Re-expose the neg
- Re-develop
- Stop, fix, water bath, and dry per the usual
I researched this quite a bit ago and found the following two sites to be quite useful in my experiments:
Originally by user67377. Source · Licensed CC BY-SA 4.0
user67377
7y ago
0
Generated from our catalog & community — verify before relying on it.
A positive can be made from normal black-and-white negative material by using a reversal process instead of standard development. The basic idea is:
- First develop normally, so the exposed areas become metallic silver.
- Bleach away that developed silver.
- Re-expose the material to light, which now affects the remaining unexposed silver halide.
- Develop again, so those areas become dark.
- Fix and wash as usual.
This reverses the tonal relationship, producing a positive rather than a negative.
Why it works: after the first development, some silver halide remains unexposed. If the developed silver is removed and the material is then fogged by light, that remaining halide can be developed, creating image density where there was little or none before.
Results depend on the material. With film, this can produce a direct positive transparency. With paper, you can get a direct positive print of sorts, though purpose-made direct positive papers are more common for practical use. In general, the look and contrast may differ from normal negative-to-print workflows, since ordinary negative materials are optimized for standard processing, not reversal.
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