The two pieces of cardboard, wrapped in paper or cloth, that make a hardcover book hard. The term board is used because originally, the boards were made of wood. In about the middle of the 18th century, as cardboard became available, book binders began using it, as it was much easier to work with, and almost as strong as wood. Some of the books with wooden boards have bindings that are just leather and exposed wood, showing the beauty of the tree. Good imitations, some even surpassing the beauty of the trees, have been done with leather made to look like a maple burl.