Handmade papers like washi have always presented challenges for me, the handcoating emulsion dude. Did they have enough size? Would the paper fibers cooperate with the chemistry? One paper would work well with Vandyke brown, actually really well, but be horrible with cyanotype.
The latest struggle was when a good paper turned bad. For the last six or seven months I have been struggling with a change in my favorite paper. When I first started using the Kozo Unryu paper there sometimes were 2-4 pinholes on half a full sheet but the last batch would have 15 to 20. These pinholes would act like a drain in a sink by pulling the photo chemistry I was applying out the back side of the paper. The result was a larger, lighter spot on the front of the paper. On the backside of the paper, corresponding ovals of chemistry would show up, evidence of the drain effect. These would process out after fixing the image but the light spots on the front would remain.
When I first started using the paper, I could easily spot 1-4 spots that would occasionally show up. But the lates batch would easily result in up to 12 or 15 light spots that were too much for me to carefully touch up.