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Two-Bath Pyrocat HD

Sandy King, August 2014. This page is a summary of his article, rewritten here. The original is by the author.

Two-bath development has a long history, dating to the 1880s, and was popular with 35mm and roll film in the 1930s and 1940s. This method simplifies the use of Pyrocat in two baths for black-and-white film, aimed at photographers who scan their negatives for digital printing.

For the step-by-step processes, see the Methods page.

Theory

Solution A holds the reducing agents without alkali, so little or no image forms in it. Solution B supplies the alkali, and development happens there. With Pyrocat, the sulfite in Solution A is not alkaline enough to activate the reducers, so highlights exhaust quickly in Solution B. The author reports full effective speed, strong compensation for high-contrast scenes, a long straight-line curve and high acutance.

Advantages for Scanning

  • No field notes are needed to identify individual sheets
  • Film of the same type can be developed together at the same time and temperature
  • Negatives develop to a lower average gradient, which the author links to finer grain and better sharpness
  • The negatives scan well on consumer flatbed scanners

Film Behaviour

Different films respond differently because of emulsion hardening. The author notes the contrast differences are small enough to correct in Photoshop.

Contrast Control

In order of efficiency:

  1. Change the working-solution dilution. Weaker dilution lowers contrast, stronger dilution raises it.
  2. Lengthen or shorten development time.
  3. Raise or lower the temperature slightly.

Metering

Base exposure on an incident reading taken in the darkest area where you want shadow detail, with the meter dome pointed at the camera lens.

Film Test Data

The article includes CI charts showing average gradient and effective film speed for each film at set development times, using Pyrocat-HD at 1+20 and 75°F with constant agitation. The author recommends choosing a time that gives an average gradient of about 0.52 for scanning.

The author advises testing with your own film and fresh developer before developing important negatives.