Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

back cornering

The process in bookbinding of cutting away a small triangular piece of the head and tail edges of the boards of a book at the joints. The cut is made at two angles, one to the board edge and the other to the thickness of the board. The amount removed and the angle of the cut are determined by the width of the leather turn-ins and their thickness where they meet the edge of the board. The purpose of back cornering is to relieve the strain on the joints of the book when the covers are opened; otherwise, a strain would occur because of the additional thickness of the leather caused by the turn-ins. Back cornering also facilitates setting and shaping the headcaps. Back cornering was at first done on the inside of the boards, allowing for "laced-in" headband cores or tabs. By the late Middle Ages, back cornering was a standard procedure for books with folded-down or stubbed cores. The modern method of cornering on the outside surfaces of the boards facilitates the current method of headcapping and probably stems from the 18th century. (237 , 335 )