I have tried exposing the paper and my highlights are just blue.
I've used several types of artists paper available in pads from Hobby Lobby. We don't have many options for paper near me. Although, in my limited past, I never experienced this on any type of paper. I can see some issues caused by paper but these look almost as if they have already been exposed and washed.
I picked up some Arches hot pressed water color on my way home from work and will try coating tonight and see how it goes. I also have some Hahnemuhle platinum rag on order.
First a confession... I am a paper snob! This snobbishness comes about from many years of alt process printing.
Generally, student or hobby grade papers that are commonly available at the big chains are not suitable for alt process printing. They are often made from inexpensive pulp and can contain all sorts of additives which interfere with alt process chemistry.
Mike Ware has a somewhat dated article describing the characteristics of a good alt process paper, see:
https://www.mikeware.co.uk/mikeware/Alternative_Printing.html
For alt process printing stick with higher grades of paper made from alpha-cellulose (a purified form of wood pulp) or cotton rags. How do you know when a paper is made from these pulps? The manufacture will tell you! These materials are the mark of quality papers and the manufactures will want you to know!!!
There is one hitch to worry about with these papers though. That is that many 'art' papers include calcium carbonate to protect them from long term exposure to acids in the environment. This carbonate is incompatible with most alt processes. However it is easy to remove by pre-treating papers with an acid (as others have mentioned).
One can also avoid the "carbonate problem" by (again, as others have mentioned) using a paper designed for alt process printing. Hahn. Platinum Rag, Arches Platine, Legion Revere Platinum and Bergger Cot are the four ''biggies" in this arena.
The Arches watercolor paper you bought is a carbonate buffered paper and thus is not likely to work with standard cyanotype procedures without pre-treatment with acid. However, if you 'develop' your cyanotype using acidic conditions instead of plain water it may work for you. See this post, by yours truly, for some additional information on this topic:
https://www.photrio.com/forum/threa...on-of-paper-for-traditional-cyanotype.176816/.
Additionally, you can find much more information about papers for alt process here:
https://www.alternativephotography.com/paper-and-artpaper/. Specifically, Chris Anderson's article (
https://www.alternativephotography....sic-cyanotype-process-1613-research-for-free/) will be of particular interest.
Regards,
--- Frank