Why does the blue paint look like this?

[ReneZ]

The blue pigment consists of tiny crystals, but there is some kind of a liquid medium needed to apply it to the parchment. I have the feeling that this medium is changing or has changed colour, and went through dark green to dark grey. It has also stained opposite pages more than any other pigment.



I suppose there can be different reasons for this frequent staining, but I lack the knowledge to explore that.


(Image removed, I already posted it before)