a novel featuring a blind seer and a young girl, may include a shady salesman/magician with a name like Petrichor

I don't recall much about this book. But the cover may have featured the blind oracle, who was a young homeless boy, may have been bound to the shady salesman/magician. There's a scene with a box full of quicksilver, which the girl uses as a mirror and is enchanted by in a dangerous manner. She may have had a brother. There may have been a bird included that had been blinded so it wouldn't know when it was dark but that could be something else. The boy is described as pale with completely blank, empty eyes (no iris, no pupil).

I read it in the mid-2000s, I believe it was set in Victorian times

EDIT: the magician could have been named Malakir