Quote Originally Posted by GGardner View Post
Are you sure that's right? I was hoping that reciprocity failure would (for once) be a big help in this kind of project.
Ok, I just crunched some theoretical numbers without considerung reciprocity, because it is very much neglectible for paper... Something around 0,001ASA (still around 12-13 steps below regular paper) might be good enough but it's still very unrealistic, considering modern papers have around 5-15ASA. It's also almost impossible to calculate the exposure reliably without massive testing. Reciprocity is documented for up to a few hours, but after that it becomes guesswork. More work than it's worth, in my opinion.

Cyanotypes might be an idea, though, with their relatively low sensitivity and easy processing. I haven't done them myself, so others will know a lot more.