Sewn vs Glued Book Binding: How Signatures Become a Book

Every bound book starts as a stack of folded sheets. What happens next, whether those sheets are sewn together with thread or held by an adhesive along the spine, shapes how the finished book opens, how it handles repeated reading and how it ages on a shelf. For print shops producing short runs, choosing between sewn and glued binding is a practical decision about the life the book is expected to have.

From printed sheet to signature

A large printed sheet is folded several times to create a group of pages called a signature, also known as a gathering or section. Library conservators use the word gatherings when they describe how a book is made. In the training notes published by the University of Reading’s Special Collections Service, a graduate trainee describes learning bookbinding as a way to understand repair, and producing a simple book made of several gatherings of paper.

The number of folds determines the format. Terms such as sextodecimo (16mo) or 64mo describe how many leaves come from one sheet, and therefore how small the resulting pages are. Once printed and folded, signatures are collected in order in a gathering step so that the book block reads correctly from first page to last.

How thread sewing joins the gatherings

In thread-sewn binding, often called Smyth sewing after the machines that popularised it, each gathering is stitched through its fold and linked to its neighbours. The thread runs along the inside of each fold, so the pages remain physically attached to the spine through the paper itself rather than through a single glued edge.

Historically this work was done by hand. The Reading conservation post notes that while gatherings in new books are joined together by machine, before the mechanisation of printing this would have been done by hand. The same post explains that sewing around pieces of tape gave the spine more strength, which illustrates a basic principle: the structure of the sewing is what carries the load when a book is opened and handled.

Modern equipment brings this structure to short-run and digital work. A book sewing machine such as the SF-3400DP from Digital Finishing Systems is designed to sew book blocks that have already been gathered in gathering machines, and the manufacturer states it was specially designed for digital printing and on-demand printing. According to its published specifications, it uses thin needles and dense needle sets, can sew formats from 16mo (horizontal and vertical binding) down to 64mo, handles sewing sizes from 100×100 mm up to 340×310 mm, runs at 45 cycles per minute and supports up to 8 needle sets at a 19 mm interval.

What glued (perfect) binding does differently

In perfect binding, the folded edges of the signatures are typically trimmed or roughened and a layer of adhesive holds the individual leaves together at the spine. It is fast and economical, which is why it is widely used for paperbacks, catalogues and reports. The trade-off is that the pages depend on the adhesive and the spine edge rather than on thread passing through each fold.

Adhesive also plays a role in sewn books, but differently. In the Edinburgh conservation example discussed below, the old volumes had sewn text blocks with animal glue on the spine. The glue consolidates the spine, while the sewing keeps the sections connected.

Why sewn books open flatter and last longer

Because each gathering hinges at its own fold, a sewn book can be opened with the stress spread across the thread and the folds. This is the reason sewn bindings are generally associated with books that open more comfortably and tolerate repeated use, such as reference works, cookbooks, manuals and books meant to be kept.

Even sewn books have limits. The University of Edinburgh conservation team describes a collection of Latin theses from 1726 to 1826 in which 46 volumes had broken sewing, leaving text blocks broken in half or in three or four separate pieces. The cause, according to the conservator, was repeated use and forcing the volumes open. Their repair involved removing the spine, softening the animal glue with wheat starch paste, then relining the spine with four layers of medium weight Japanese paper and a layer of archival paper for added strength. Even after repair, the books were digitised on an angle support at 90 degrees to put less pressure on the spine.

The lesson for producers is twofold: sewing is what holds a book together under heavy handling, and how a book is opened matters as much as how it is made.

Repairability and the long view

Conservators value structures that can be repaired. The Reading post stresses that the most important part of rare book preservation is using water soluble materials so that a repair can be reversed if necessary, which means Japanese paper and paste rather than superglue or adhesive tape. A sewn book that loosens can often have its gatherings sewn back in, as the Reading trainee describes learning to do with loose pages.

Choosing the right method for a job

• Expected use: books opened often or kept for years benefit from thread sewing.
• Opening behaviour: if readers need the book to stay open on a table, sewn signatures are the stronger choice.
• Run length and format: modern sewing equipment for digital and on-demand printing makes sewn binding practical for smaller runs and small formats.
• Budget and speed: perfect binding remains efficient for short-lived or high-volume items.

Sewn and glued bindings both have their place. When a book is expected to be read hard and kept, the conservation record suggests that thread through the fold, combined with careful handling, is what keeps the gatherings together over time.

Sources

• blogs.reading.ac.uk, Book binding for beginners: conservation training. https://blogs.reading.ac.uk/special-collections/2013/11/book-binding-for-beginners-conservation-training/
• libraryblogs.is.ed.ac.uk, A Book of Two Halves. https://libraryblogs.is.ed.ac.uk/conservation/2017/02/16/a-book-of-two-halves/

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