Well, my experiment with pre-acidification of Rives BFK for doing palladium/platinum/Ziatypes was a success. I got a flawless Ziatype over which I will now try several gum layers. My pre-acidification consisted of a 5 minute bath in 5% Oxalic Acid. I sized the paper AFTER the acidification bath. Image to follow.
Here is the image with the first two layers of gum over Ziatype. Colors are Alizarin Crimson and Sepia. I’m planning on doing at least two more layers, probably another sepia or burnt Sienna and then another red, maybe something deeper red.
dcphotoartist 
I wonder, if that will affect the archival stability of the BFK?
To the best of my knowledge it does not. Most watercolor papers are buffered to make them somewhat basic. The pre-acidification gets them back to pH neutral.