Furthermore, the angle of conformation of the spine caused by backing probably provides for better vertical standing support of the text block.
Backing may be accomplished by hand with the use of a BACKING HAMMER or, in the case of edition and library binding, by means of a ROUNDING AND BACKING MACHINE . In some cases e.g., very large books, backing may be done in a BACKER as a separate operation.
Some authorities consider the backing of a book to be the most important and difficult of all the processes in the craft of hand bookbinding, and poor or inadequate backing is certainly one of the major sources of problems in the processes of edition and library bookbinding.
Although books dating from at least as early as the beginning of the second half of the 15th century were often rounded, backing for the purpose of forming shoulders seems not to have been an established procedure before 1500, or perhaps somewhat later. It is uncertain when bookbinders discovered that rounding and backing was a superior bookbinding technique. The swell caused by sewing sometimes causes books to assume a slight round with no effort on the part of the bookbinder, and, over a long period of time, the pressure of the boards perhaps even results in the effect of backing. (209 , 236 , 335 , 339 )