The short-lived, and difficult to categorize, Pantachrom process may seem like a curiosity, with little lasting impact today. However, the process remains historically and didactically intriguing. It united principles of bipack motion photography (employing green and blue sensitized lenticular front film with red-sensitized back film, along with two-color band filters) for recording, and eventually contact-duplicating, the three color records – captured with said bipack – onto a print stock with three emulsion layers. In the latter printing step, the process combined the silver dye bleach process for two of the primary colors, with iron-blue toning of a conventional emulsion for the third primary – essentially bringing together two very different basic principles for both three-color recording (lenticular and bipack) and printing (chromogenic and toning), respectively.

Filming

As described by Eggert and Heymer, a lenticular bipack was employed in photography, with two strips of film sandwiched together in the film gate, emulsion-to-emulsion. The film was shot in a bipack camera where special attention was paid to the film transport, pressure, and registration of the bipack film for optimal results. The front B/W lenticular reversal film was sensitive to blue and green light, while the back B/W negative film was predominantly red sensitive. Both the front and back films of the bipack were optimized for reduced transmittance, to curtail the adverse effects of halation (diffusion of light).

Although working according to a two-color principle, the band filter attached to the camera lens employed three alternating yellow-magenta-yellow filters – resulting in alternating green and blue rows of color separation of roughly the same width. Following the additive principle, this use of the yellow (red + green) and magenta (red + blue) filter bands, allowed red light to pass through the front lenticular reversal film unaffected to reach the back negative film, ensuring the recording of the red part of the spectrum. This filter arrangement could also be altered to magenta-yellow-magenta bands – depending on whether the shooting used daylight, or carbon arc light sources, to optimize sensitivity. Furthermore, the lenticular front recording film was produced by a casting process that produced a 43µm spacing of the vertical cylindrical lenses – which was 54% larger than the 28µm spacing of 16mm Agfacolor lenticular film – combining enhanced color separation with the higher spatial resolution afforded by the 35mm stock.

The front lenticular recording film of the bipack was processed as a B/W reversal film to produce a positive image. This resulted in improved contrast of the screen process’ lines, and better compensation for color losses that were caused due to light scattering in the emulsion layers. The back recording film was developed akin to a usual negative. The sensitivities of the emulsion layers were adjusted to harmonize for both daylight and carbon-arc photography, as per shooting conditions. Any remaining differences were compensated for in the copying process.

Printing

After shooting, each of the color separations recorded on the bipack film were precisely contact printed onto the designated layers of the Agfacolor Tripo copy film (which contained two layers of emulsion on one side of the film and another layer on the reverse side) using subtractive principles. From the front lenticular recording film, the blue separation, intended for the red-sensitive yellow layer of the Tripo film, was copied with red light; and the green separation, intended for the blue-sensitive magenta layer of the Tripo film, was copied with blue light. The red separation recorded in the back negative of the recording film was subsequently copied to the layer on the reverse side of the Tripo film using blue light. In this case, the color of the light used for copying was not directly related to the color of the resulting dyes. These printing light wavelengths were intricately chosen in order to avoid interferences between the different layers of the Tripo copy film. The directionality of the copying light striking the front film, optimal placement of the copying filters, and accurate registration of the film during the copying process, were all critical to achieve the desired results. 

Following the silver dye bleaching process, the developed silver in the yellow and magenta dye layers of the Tripo film were bleached out, without affecting the unexposed silver bromide. Therefore, these areas represented a positive color image identical in proportion to the developed silver, removed in the process of bleaching and fixing. The rear emulsion of the Tripo was subsequently toned using iron blue, which was opaque in the infrared spectrum. This conveniently solved the problem of sound reproduction prevalent in subtractive processes of the time – which resulted from the transparency of the organic dyes in the red and the near-infrared spectrum. Although the Pantachrom process used the same Agfa Tripo film that had been developed for the Gasparcolor process, Gerd Heymer suggested that the lengthening of the processing time caused by the iron blue toning was compensated for by the simplified development of the backing layer – and, additionally, produced higher luminosity and color stability.

By early 1939, the sensitivity of the bipack films had further been improved, and the brilliance and light stability of the “Tripofilm III” led to considerable interest from the advertisement industry, with 98 copies ordered for a cologne commercial, and two hundred for a cigarette one, respectively – yet a comparative analysis, from January 1939, proved it somewhat inferior to Technicolor. Regardless of further chemical improvements, Pantachrom had to yield to the Agfacolor process and the comparative ease of its recording.