Because the two processes mentioned in the OP are so very slow and by slow we are talking about exposure times for cyanotype prints of from several minutes to several hours. Trying to get that much UV light thru the small aperture of an enlarging lens would take a very long time. This is also in addition to the fact that most glass formulations do not pass much UV light. UV spectrophotometers use cuvettes (special liquid containers) made of fused silica instead of glass. Remember too that UV light degrades most plastics including those used for film base. So one needs to limit the exposure time. If a copy negative is lost it is only an inconvenience not the loss of a precious image.
Originally Posted by MDR
Any silver halide emulsion is orders of magnitude faster than the two processes mentioned. BTW emulsions do not have to be sensitized to UV light which is in their normal sensitivity.
Todd Gangler moved into his carbon printing work as a result of working with the Fresson lab on an early project.
learn something every day thanks
Originally Posted by Hexavalent