The Mortensen Pigment Process
From Mortensen's extensive handwritten notes it is evident that he and George Dunham worked closely in the myriad experiments to develop the pigment process for which WM became famous. The following pages reveal, in Mortensen's own hand, some of the painstaking steps that were taken to find just the right set of ingredients and proportions for coating the paper. In Chapter V of Robert Balcomb's book, Me and Mortensen: Photography with the Master, Robert writes:
During the time for washing and drying the diapositive and paper negative, Mortensen did preliminary work. He attached a sheet of Strathmore watercolor paper (any good paper will do) to a wooden board with a pin in each corner. He then painted on a mixture of gelatin and Vano starch so that no moisture would soak into the paper, similar to an artist applying gesso to a canvas. After it was dry, he coated the paper with a mixture of watercolor pigments and a sensitizer.
He took it into the darkroom to dry (this kind of sensitized emulsion becomes light sensitive when dry). He then placed the paper negative face-down on the face-up pigmented paper, sandwiched them between two sheets of heavy glass, clamped it all together with strong rubber bands, took it outside into the hot southern California mid-afternoon sun, and laid it on the ground, paper negative on top. By his experience, he guesstimated a 2-1/2-hour exposure (this emulsion is extremely slow).
Sunlight has a high degree of UV for its reaction to the sensitizer in the pigment emulsion. The sensitized pigment receives UV to the same degree as the lights and darks in the paper negative. Dark areas in the paper negative prevent the light from penetrating through to the coated pigment paper. Light areas allow the light to go through to expose the sensitized pigments.
Back in the darkroom under room light, Mortensen removed the paper negative, dampened the exposed pigment paper, turned on the hot water, and, with a fan-spray, sprayed the paper gently, back and forth. Where heat of sunlight reached the emulsion, it hardened those areas, so they did not wash off. Where no light-heat reached the emulsion, the water washed off the pigment, leaving areas of the white of the paper to the same degree of light hitting the surface. Gradations of tone are preserved. What is left is the pigment print. Traditional developing needs chemical developer—this pigment process does not: Water is the developer. Retouching is simply with charcoal pencil. The result is a beautiful print similar to a bromoil or a fine lithograph. [excerpt ©2012 Amphora Editions]
In the following notes, certain letters and words appear which may not be familiar. Here is a key to identifying some of them (others are a complete mystery):
Knox = Knox Gelatin
Dist. = Distilled water
Vano = Vano starch
Wold = Wold Lamp Black
W.N. = Winsor & Newton