Yes, fingerprints and/or contamination also could be the cause of the problem.
Just wanted to mention that not always you get image loss; for instance, with Masa paper and traditional cyanotype I get stronger image where I touch the paper! Puzzling... Anyway, you somehow get image loss or insensification (therefore uneven sensitizing) when you touch the image area while handling the paper. So, avoid it.
Stonehenge as I know it should be a good paper for Kallitypes and Vandykes, but I have quite old stock on hands (> 5 years). Maybe the paper have changed since I last purchased it???
I think you'll definitely find the remedy. We have all supplied good hints/suggestions. I never ever got such marks in my practice. Please return back to us if you manage to sort out the problem.
P.S. Change "ilfosol" to "ilfotol" in my first message. That was a typo...
Originally Posted by snallan