If I had one of Blake's printed books I would not write in it. But, any other book is to be highlighted, underlined, and annotated. I don't dog-ear the pages, but cut thumb indexes directly to vital passages--there aren't all that many in most books.
"(William) Blake, however, created his plates by first painting his texts and the lineaments of his illustrations and decorations upon copper sheets with a very fine brush dipped in a clear acid-resist liquid. (He said that the technique had come to him in a dream.) After painting the text and decoration, he immersed the plates in acid, which ate away their unpainted (that is, unprotected) areas."