I tried the Arches Aquarelle 90lb Bright White Hot Press tonight.

First attempt: Sensitize paper (New Cyanotype + tiny drop of photo-flo) turned green after 5 minutes. Fail.
Second attempt: Bath paper in citric acid bath for 5 minutes. Dry. Coat with sensitizer. Turned green. Fail.
Third attempt: Precoat with 40% Citric Acid w/v solution. Dry. Coat with New Cyanotype + tiny drop of photo-flo.
- didn't turn green
- no mottle or speckle in final image
- citric acid overcoat made even coating of sensitizer harder to do
- still some wash-off of Prussian Blue
- final density not so good (worse than regular cyanotype)
- my fingerprints would lift the Prussian Blue off the paper while it was wet.
- densities were better than Arches Platine. Absorption was better than Platine.

Hmmm.....

Buxton paper is out of stock until fall. Weston Diploma seems to be gone. Ideas on a non-buffered paper I might try?