[Note: This post is about the chemical known as "prussian blue," NOT about the neo-Nazi band Prussian Blue. Thank you.]
"The pigment is used in paints, and it is the traditional 'blue' in blueprints. It has been used as an antidote for certain kinds of heavy metal poisoning."
Can you think of any other gorgeous art supply that also saves lives? Pens with listening devices à la James Bond don't count.
Prussian blue, you're my hero.