I'm only half joking about the central role that the contact printing frame plays in alternative processes. The need for this piece of equipment illustrates some fundamental points in common for various popular processes.
First, many alternative processes are only sensitive to UV light. Because of the impracticality of producing a UV enlarger, you must have a negative the size of the print you want to create - and that negative (emulsion side) must be held tightly against the sensitized material. Enter the contact printing frame.
Second, there are some practical mechanical issues in constructing a simple contact printing frame. These devices are virtually unchanged since the early days of photography - a piece a clear glass in a wooden frame (I've been told you can sometimes find antique Kodak models at flea markets being offered cheaply as oddly constructed picture frames). Typically utilizing metal springs on the back to press the negative into contact with the sensitized surface, the ability to get a uniform contact is more difficult the larger the frame - with 16" x 20" being considered the practical limit for a mechanical frame. Given the difficulty of traditionally creating large negatives for contact printing, and the difficulty in ensuring good contact mechanically between the negative and the sensitized surface, it is the case that prints tend to be of a modest size (8"x10" or 11"x14" being popular standard sizes in the past).
Third, contact printing frames typically boast a hinged split back. "Why?" you may ask. The purpose is to allow you to check the progress of the exposure by loosening half the back, folding it away and looking at the emerging print. Many alternative processes exhibit either a partial print out (as in palladium printing) or a full printing out (as in Printing Out Paper - POP).
The third point is a matter of great practicality. I bounce back and forth in conversation between the terms "alternative" and "historical" printing processes. Most of these alternative processes were also some of the earliest practical means of reproducing multiple prints from an original image. The readily available form of UV light was of course the sun. The intensity of sunlight varies by time of day, by season, and by weather. It's a wonder that much early progress was made in England in photography given the weather I've seen there. With exposures often measured in many minutes, the progress of the printing was periodically checked by ducking indoors or into shade with the printing frame, opening up half the back, and taking a look. And then returning to complete the exposure.
Starting with cyanotypes, and a small used contact printing frame, one can enjoy the sun and explore alternative photography cheaply.
Enough of these asides - in the next entry, let's just simply make a print.