I am relatively new to making cyanotypes and have begun simply by using kits from Bostick Sullivan. After a lot of exposure tests, I've made some images I really love.
While I was washing some of the prints, dark blue splotches appeared in some of the highlights, but these went away when the prints dried. After hanging on my wall for several weeks the splotches are reappearing.
I'm guessing that the problem is that the paper may be alkali. Is it too late to re-wash the prints with vinegar, lemon juice or something else? If I can re-wash, what concentrate should I use, for how long, and should I follow with a water wash?