I've read them years ago. It was a trilogy, or it was when I read it, of fantasy novels. There was a Will in it, and an Allison. They were two of the main characters, can't remember what the name of the main main character was. She was a witch by the way. The novels had something with either an iron witch or an iron sea, maybe both. And I believe it had something to do with a world behind a painting, though I'm not very sure about that. Anyone knows what I'm talking about?
Could it be the Madeline L'Engle books? She wrote "A Swiftly Tilting Planet", "A Wind in the Door" and I can't remember the title of the other one now.