Friday, May 11, 2007
Archaic non-silver printing processes
Some of the earliest methods of photographic printmaking are non-silver processes. While they are no longer used for everyday printing, most of these processes can be used to make prints by anyone willing to put in the time and effort to master them. There are too many archaic printing processes for me to describe here, so I’ll limit myself to short descriptions of some of the better known ones.
Cyanotype prints have a distinctive blue tone. The chemicals used to mix a cyanotype emulsion create Prussian blue pigment when combined and exposed to ultraviolet light. The prints shown in this post are cyanotypes that I made last summer.
The deep brown tones obtained in a VanDyke brown print also come from the chemicals used to mix the emulsion. Different chemicals result in the brown tones when the sensitized print is exposed to ultraviolet light.
Gum bichromate prints are also created by coating paper with a light sensitive emulsion. In these prints, however, color is determined by the addition of watercolor paint to the liquid emulsion. Different colors on the same print can be obtained by coating and printing the paper multiple times.
Cyanotypes, VanDyke brown prints and gum bichromate prints are contact printing processes. This means that the resulting print is the same size as the negative used to print it. Enlargers are not used as in traditional printing. If you desire an 8 X 10 inch print, you must print from an 8 X 10 inch negative. Currently, the easiest method of obtaining large negatives is to print them onto transparency film using a photo-quality inkjet printer. Creating the negative with the correct density and tonal range requires experience in intermediate to advanced level Photoshop skills.
To prepare a light-sensitive surface for printing, chemical solutions are mixed and brushed by hand onto paper or fabric (printmaking and watercolor paper are commonly used). The paper is then allowed to air dry. After the paper is dried, the negative is placed in contact with the sensitized paper, and exposed to ultraviolet light. Exposure times vary based on the intensity of the light source you are using. For cyanotype prints, an exposure time of 20 minutes in direct sunlight is not uncommon. I built a simple exposure unit equipped with ultraviolet bulbs, using this, my exposure time for a cyanotype is 11-13 minutes.
Development for these processes is usually more simple than it is for traditional photographs. The three processes I’ve described all develop in water. After a 3-4 minute rinse, cyanotype prints are submerged in a bath of diluted hydrogen peroxide, which oxidizes the Prussian blue pigment, resulting in a darker blue color.
A more detailed description of these and many other process can be found on the Alternative Photography website, along with many examples of work made using these processes. Follow the link to the right.