Van Dyke/Kallitype process 3 - Exposure

Exposure of the coated paper requires a full-size negative and ultraviolet light. The enlarger just won't work for this process! You must produce a contact print, and thus a neg that is the same size as the image you want. This process calls for negatives with quite a wide density range (up to 1.85). You can create the negative through the usual photographic steps in a darkroom on large format sheet film (I have been using 50 x 60 cm film).

Another method which I am using is to create the large negs using Photoshop and inkjet printing onto transparency film. It works surprisingly well if you are proficient with computer graphics software and have the equipment. I scan images on my Minolta Dimage II high resolution film scanner. The major limitation is the output size of the inkjet printer. I'm limited to 8x14 for these negatives unless I do mosaic printing, spreading the image over two to six 8x10s or 8x14s. If done carefully, this has worked fairly well, though there may be a slight line where the sections come together.

I constructed a large UV exposure unit using eight 48" UV blacklight bulbs mounted on a large frame. The negative and coated paper are sandwiched in a glass exposure contact unit which I also built. My exposure times range from 2 minutes to 6 minutes. Your exposure times will mostly depend on the intensity of your UV source and the overall density of the negative. For Van Dyke/Kallitypes underexposure is preferable to overexposure (the opposite of cyanotype).

The paper can be inspected during the exposure if the negative and paper are taped down securely. After many kallitypes, I have begun to get a feeling for how long is needed. Since the print will darken considerably in development and fixing, you need to stop exposing when the image is still quite light. The best thing is to coat some test strips and try several exposures before proceeding.

Van Dyke/Kallitype process 4 - Development and Processing