I recently finished working as an Artist-in-Residence at RayKo Photography in San Francisco, and my instructable is based on the work I was making there. RayKo has the only large-scale color processor that is publicly accessible on the west coast - and with my time at RayKo I was interested in experimenting with different ways of utilizing it. The processor keeps all of the color darkroom chemistry at exactly the correct temperature, allowing for consistent results from one print to the next. It also makes color printing much easier; you load a print into the machine on one end (the end you don't see here which is in the dark) and then after five minutes it arrives on this other side, dry and ready for inspection.
It would be possible to make Chromogenic prints without a fancy enlarger and processor, but your results (focus, exposure, and colors) would all be harder to control, and to make large prints you would need a considerable amount of space. Here is a good instructable on creating a home darkroom, to help get you started.
Step 1: The Very Dark Room
Here is a diagram of a typical 35mm enlarger, and then a photo of me loading the negative carrier into a large format (8" x 10") color enlarger. Although the size is very different, the basic idea is the same. From top to bottom you have: a light / lamp house > negative carrier > lens > space for the light to travel > plane where you put your paper for exposure / easel. The space between the enlarger head and the easel (and the size of lens used) decides the amount of magnification. The amount of space between the negative carrier and the lens adjusts the focus. The main difference between these two enlargers is size, which allows for making a print from a larger negative, and also allows for making a larger print.
Step 2: Chromogenic Paper
The processed used to make most traditional photographic prints (non-digital) is called Chromogenic. Like Black and White darkroom printing, silver halides are exposed in the paper, but with color paper they are coupled to one of three different colors of light: Red, Green, and Blue.
Chromogenic paper has become harder to find, but is still sold both in sheets and in rolls. I am lucky to live close to a warehouse in Oakland, CA where quite a variety of paper is sold and stored. Because I am interested in creating large mural prints, I buy my paper in 30" rolls. Kodak "N" surface is the most matte surface available. The rolls I buy are 30 inches wide, and 164 feet long. Roll paper is also cheaper as they charge a premium for having it cut down.
Step 3: Working in the Dark
Color printing must be done in complete darkness, which makes basic things like cutting paper, finding tape, or walking a few steps in the correct direction challenging and new. Before turning out the lights to make a print, I like to double check that I know where everything that I might need is - once the paper is out it is can be pretty frustrating to grope around in the dark.
In this photo are two pieces of important equipment. The smaller black rectangular box is the processor for the color enlarger, it is where you can adjust the color and general exposure of the image (more on that soon). The lower, larger gray box is a paper dispenser - it holds a roll of photographic paper light-tight, making it easier to access when working in the dark. The other things you see here - rulers, a step latter, scissors - are all helpful tools when printing.
Step 4: Timing = Exposure
Once setup, the first thing to do is to create a test strip to get a sense of your exposure time. Here is a test strip showing 5 second increments of 20, 25, and 30 seconds. I created this test strip by covering the paper with an opaque piece of cardboard for 5 second increments. This strip is about 6" tall and 15" wide. It can be tricky to judge the exposure by a section of the image, as my final image will be about 30" x 55". In general, I will try to place the paper in a high-contrast area; allowing me to see the highlights and shadows in one section. In most cases I am looking to keep the highlights from being "blown out" (bright white) while also not wanting to loose detail in my shadows.
Step 5: Color
Getting the color right can be tricky. The three colors that can be controlled in Chromogenic printing are Cyan, Yellow and Magenta. What is actually being controlled is the amount of filtration for each color, which means that by raising the amount of magenta filtration, you are actually lowering the amount of magenta in the print. In addition, It is standard procedure to leave the cyan at zero. By controlling the amount of magenta and yellow in a print, you can actually control all the color in the image.
In this test strip you can see the image has become significantly less red than it was for the "time" test strip. I accomplished this by raising the amount of magenta filtration, as well as lowering the yellow. Unfortunately, there is no easy way to test multiple color filtrations on one test strip, and so the process can be time consuming.
Step 6: Onion Rings
Where my process parts from traditional photography is in what I am choosing to make a print from. Traditional photographic enlargers were created to enlarge a photographic negative. I have been experimenting with putting different objects into the enlarger head where the negative would traditionally go. After much experimentation I have been most excited by enlarging objects from everyday life - things that most of us interact with on a regular basis, yet rarely consider for their beauty. My first moment of excitement came when I foolishly put some onion rings into the enlarger, and created this celestial print from them.
For the most part I am treating the onion ring like a traditional negative - the colors that print are the inverse (negative) of the original. Where the onion ring is yellow, it will print blue. Where it is green, you will get magenta. Each image I make has an element of discovery and surprise for me as I print it.
Step 7: The Final Product
I am delighted to be making these unique old-school prints created directly from different aspects of daily life. That said, this process of creating work is available to everyone. Chromogenic printing is an interesting and viable way to create unique works that will withstand the test of time. I hope that I made the process and technique more available to you through these instructions.