I am making cyanotypes using the traditional formula and have been using Winsor & Newton sheet watercolor paper simply because I have a large supply of it. My understanding is that it is buffered with an alkaline filler to keep it acid-free, and while this is great for watercolor and other art media, this makes it bad for cyanotype and other iron-based photo processes. I am trying to figure out how bad, and if really bad, then what are alternatives that aren't as expensive and hard to get as Buxton.
In searching this site and others for recommendations for papers to use for cyanotype I am having trouble telling how important it is to use an unbuffered paper. Mike Ware goes into detail and has had Buxton paper created specifically to avoid this type of problem. However, I am finding that many experienced cyanotypists recommend Canson Montval, Stratmore 400, Arches Aquarel and Rives BFK, and as far as I can tell, most if not all of these papers ARE buffered.
So are these often recommended papers buffered with something that won't interfere with the cyanotype's sensitivity to alkalis? Are they buffered with calcium carbonate but it doesn't matter if you can get a good looking print out of them? Or will my prints, which look fine to me now, start fading alarmingly in five, ten, fifteen years due to the lurking menace of calcium carbonate?