I have just acquired a Philips solarium to use to expose cyanotypes. I have done a search and found widely different guidelines for timings and distances (anything from 55 seconds to 30 minutes and 1" to 12" distance from the negative).

I am thinking the best bet will be to try a kind of maximum black (or rather maximum blue) test with a few strips of paper and a blank negative say starting at 6" distance and exposing for longer and longer as one would with an enlarger and paper. Does that make sense to anyone to establish a base time?

My second question concerns the maximum size of print. If you pull the lamp back far enough (it has 12" tubes) could you conceivably expose an 11x14" print with a suitably longer time. That is the maximum size I would ever intend to go (and not for a good while yet). Does the inverse square law apply to UV?

My final question concerns making my own unit. Can one use ordinary fluorescent units with black light bulbs? I have some 24" aquarium fittings but don't know whether it is OK to put UV intense bulbs in place of the normal aquarium lights.