Which of your papers are unbuffered and do not have gelatin sizing? Any paper with Calcium Carbonate is not usable for cyanotype, Van Dyke or other iron-based processes. This means these papers are not considered ISO archival. ISO standards call for Calcium Carbonate. So by default, if a paper is ISO archival it isn't suitable.

Thanks!

We recommend the Revere Platinum paper as this was created to be used with alternative photo processes. Revere Platinum is synthetically sized and contains no calcium carbonate. Here is some more information about the paper:

https://legionpaper.com/revere-platinum/

We'd be happy to send you samples. Please send us your shipping details to info[at]legionpaper.com