1, different layout: Darkmouth means that at the mouth of a book with ink, because the central plane of the book is not carved, it is still at the same level as the lettering, columns and lines in the book, and the printed paper is painted thick black, so that the folded printed paper becomes a book with a thick black mouth or a big Darkmouth, and the white mouth means that it is white at the central crease.
2. Different functions: Darkmouth is used to decorate books, while white mouth is used to mark the contents of books or distinguish layout information.