i think calotypes refer to the paper negative that was printed out onto salted paper .. ( at least that is my understanding )
i do similar things as you do ... watch unfixed sun prints change over time ... and i would love to do that with salted paper
and silver nitrate .. i find it to be much in touch with my 19th century alter ego .. i gotta win the lottery though, salted paper prints
probably cost oodles more than old expired almost free photo paper ...
thanks for suggested readings !