My Artists Handbook of Materials and Techniques claims that Prussian Blue watercolors “while generally lightfast are known to bronze with age and occasionally in acidic framing environments”.
I guess I’m not familiar with the term “bronzing”. Does this mean it will take on that iridescent metallic sheen you see when light glances off a butterfly wing? Will the blue merely be dulled or be completely compromised?
From what I remember in high school art classes, our teacher warned us that Prussian Blue mixed with any other color (yellow, for example) would produce the new color (deep green); however, over time, the Prussian Blue would overtake the mixture and turn back to Prussian Blue.
Don’t ask me how it happens; it was just drilled into us in art class. I’m sure there are some art people on the boards.
Ooooh, this one took me two whole minutes on Google. Turns out there’s a band called Prussian Blue, and I had to do a couple more refined searches.
But this page has exactly what you want to know: