Monday, August 30, 2010
2 routes to color
Both pictures here are made without a camera but they are in fact quite different, one from the other. The upper one is a chromogenic C-print, made in total darkness in the color darkroom. As a process, it could be termed a color photogram or more accurately a color luminogram, since no objects were interposed between light source and paper. It is printed on color paper, Fuji or Kodak Endura. The colors arise from what is called the chromogenic reaction. Silver halide in the photo emulsion is reduced by developer to silver particles, while the newly oxidized developer reacts with a 'dye coupler' found in each of three layers of the photopaper. These developer-coupler reactions produce dyes of the three 'subtractive' colors of white light, namely cyan, magenta and yellow or CMY. The silver gets bleached out and the dyes give the color.
The lower picture is a different beast entirely. It is a chemigram, made in daylight on black-and-white photopaper with a chemistry of black-and-white developer and fixer. Standard chemigramic methods were used: dipping and snatching. The element of luck, absent in the other picture, here was sought out and embraced; a number of attempts at achieving this image were discarded. The creation of a color picture from b & w materials cannot help but fascinate. What's going on? How does it happen? William Jolly spent many years at UC Berkeley trying to answer this and related questions. He attributes the color to the Mie effect, by which small particles - their size must be on the order of the wavelengths in the visible spectrum - reflect back incident light on a range of wavelengths from short to long, which our brain assigns the such names as 'blue' and 'red' (the references are in his monograph). These particles of course are grains of silver, reduced by developer from the silver halide in the paper's emulsion. There are not only grains of silver, there are silver-bromide complexes, silver atoms, and other short-lived forms of silver too, all of different sizes, all buffeted by an ever-changing environment of developer and fixer and the byproducts of their interactions. It is from this stew that we get our 'color'.
Chemigramists have noticed that colors may sometimes change even in the washing or drying phase of the process, when no obvious chemical assault is occurring. That is because within the emulsion, at a very local or nano level, the action between substances may continue, although at much slower rate, before equilibrating and finally damping out altogether.
There is more to be said on this, but we'll leave it for another time. It's enough to show that there's more than one way to get color with photographic materials.