That's right. The weathering begins!! Lots of research into verdigris has forced my hand to drastic measures! I've painted it digitally before, but over a fully painted model is hard.
So my formula for this is very simple.
Over a base of runelord brass washed with Agrax earthshade pick out the edges, and around a few choice bolts and points of interest, paint pure heavy temple guard blue.
Two parts temple guard blue to one part nurgling green to 1part clean water paint it all. The thinner the better, make it like a watered down ink. And you should get something like this!!