In the early 1900’s photography was dominated by black and white, and color was uncommon to see in use anywhere.
Most color processes involved taking multiple separate color filtered photos on B&W film, which resulted in long exposure times, and hard to align images. Kodak wanted to improve this process and allow standard B&W single frame cameras to take color images without any special modifications.
Kodak engineer John Capstaff began working on a two-color subtractive process that could be loaded into the camera as a “bi-pack”, two emulsion layers that could be loaded into a single film holder together. In 1915 he released Kodak’s first color film, dubbed Kodakchrome though it bears only passing relationship with the Kodakchrome many of us know and remember.
This early Kodakchrome consisted of two sheets of emulsion on glass plates, one that was panchromatic(sensitive to all colors) and another that was orthochromatic(Only sensitive to blue/green). The back of the ortho plate was coated red and placed into the bipack first, with the emulsion side aimed towards the lens. The panchromatic plate was then placed behind the ortho plate and you were ready to shoot.
The panchromatic plate was filtered by the red coating on the back of the ortho layer, resulting in a blue/green filtered image on the first plate, and a red filtered image on the back plate. After shooting, the two plates would be separated and developed as positives, dyed blue and red, and recombined to form a color slide. Since only two of the three primary colors were used in this bipack, color reproduction did not cover the full spectrum, though surprisingly lifelike results could be had.
The reanimation of dead photographic processes has always fascinated me, and when I learned of the single image bichrome process, I set out immediately to see if I could reproduce it.
Typically I do this by reading patents and articles from the time of the process, but unfortunately many details of this process are scarce, and while I’m able at this point to reproduce the end results, my process isn’t using historically accurate chemistry or emulsions.
I started out using two sheets of 4x5 film. The first sheet is Ilford Ortho Plus, an ISO80 orthochromatic emulsion meant primarily for copy work. The second being Arista.EDU Ultra, an ISO100 panchromatic film chosen mostly because its very cheap and I can experiment without burning through my cash reserves. I placed the sheets into a 4x5 glass plate holder with a sheet of red acetate sandwiched between them(Three sheets won’t fit into a standard 4x5 holder) and took them outside to shoot a suitable color subject, my 1954 Plymouth Savoy.
Because the acetate acts as a red filter, the Arista 100 becomes effectively ISO12(A filter factor of around 3), which made my first several attempts end in failure as the red layer of my negative was massively underexposed and resulted in slides too dense to use. Currently I’m shooting at ISO25 and pulling development on the blue layer to bring it’s exposure closer to that of the red layer though a more effective plan would be to replace the Arista with something that is ISO400, which would bring it’s ISO to 50 after the filter.
I developed the two sheets of film with a basic B&W reversal process, which results in two B&W slides, one for the blue/green channel, and one for red. Development and reversal will be left up to the reader to investigate, as those processes are common to all B&W photography, and outside the scope of this article.
At this point there are two paths you can take to result in a color image. The first is simply scanning the two images, and combining them into two color channels in Photoshop. This will give you a nice digital bichrome image in color you can use as any other digital photo. For the majority of people working in a hybrid film/digital process, this will be the end result. But I’m crazy enough to want to take it to it’s natural end.
To produce a final color slide, the two layers must be tinted their respective colors and recombined into a single two layer image. I’ve so far been totally unable to find any documentation on what they used to dye the final emulsion layers so it was left up to me to find a way to tint them myself. The first process I tried to tint them with was a mixture of food coloring and vinegar. The vinegar helps the dyes in the food coloring to be more readily absorbed into the slide, resulting in more even and denser color. Unfortunately the food coloring is also absorbed into the non-image parts of the gelatin and gives you a LOT of extra density to your image and making the slide very hard to view under anything but the brightest of lights.
I quickly realized this wasn’t going to result in an image I could use, so I set about trying other dying agents I had on hand. It turned out that the Berg Blue Toner worked quite well for the blue channel, dying only the image itself and not the base, which gave me a much nicer blue layer to work with. Rockland’s Polytoner has a red toner that works well for the red layer.
Finally once your two layers are dyed the only thing left to do it place them back together in register with each other and watch as your blue and red images magically become a beautiful full color slide!!