Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

rounding

The process of molding the spine of a text block into an arc of approximately one-third of a circle, which in the process produces the characteristic concave fore edge of the book. Rounding takes place after the spine has been given a light coat of adhesive, and is accomplished by means of light hammering along the spine with a round-headed hammer. It may also be done by pushing in on the fore edge while holding the sides of the text block firmly, or, in the case of library or edition binding, by means of a rounding—or more commonly, a rounding and backing machine. Edition bindings are generally rounded after the spine lining has been applied.

A book is rounded to help prevent the spine from falling in, i.e., assuming a concave shape (and a convex fore edge), which would result in severe strain on the hinges of the book. It also facilitates the outer sections being knocked over to form the backing shoulders, and, in conjunction with this backing process, helps accommodate the swell in the spine resulting from the bulk added by the sewing threads.

The practice of rounding the spines of books dates back to at least the middle of the 15th century, and, during the course of years, the "proper" shape of the round has ranged from a nearly flat spine to a highly exaggerated arc. See a/so: BACKING ;ROUND BACK . (161 , 196 ,236 , 335 )