The chemical mix that includes Prussian blue, Ferric ferrocyanide, and gives its mesmerizing dark blue colour to cyanotypes has a bewildering behavior. It’s “alive”. Magic ? Better, chemistry ! Exposing a cyanotype to light will slowly fade its colour and make it loose its contrast. Store it away for a while in a dark room and, ta-dah, it’s nearly back to its original glory.
This intriguing propriety isn’t endless though. Paper degradation combined with the colour consuming effect of light will eventually put an end to it. However, the first cyanotypes created, around 1842, still manage to regenerate somehow.
Therefore, with a little care, there’s a solid chance that your precious pieces will adorn your walls for a long time.