Structure of a commercially bound book

I've been interested in the many different ways to stitch a book's pages together. I started out by learning the structure of a book on cords, which I think is a fairly typical structure for a hand-bound book. It's far from the only one, though, with perhaps the most obvious alternative being the Coptic binding, which uses no cords. I've been compiling a gallery of spine structures in this flickr gallery, if you're curious.

Here's a structure which most artisans typically wouldn't bother to learn, since it's a mass-produced structure assembled by machine. It uses thread and is a little more sturdy than the ubiquitous glue-only perfect binding. I found it in a bonded leather Bible I was taking apart recently, and I suspect it's the structure behind most mass market hardcovers.

Why learn it? Only for re-binding purposes; in my case, the client wanted a section removed from the text block, and I had to figure out how to sew back together the two parts on either side that I had left.

As you can see, there are no cords or tapes. On the inside, at the center of each signature, lengths of thread are visible; in the book I worked on, there were four, though I've only drawn three here.

The structure has most in common with a Coptic binding insofar as the stitches are chained together by looping around each other, rather than passing around a cord or getting sewn through a leather spine.

Unlike in a Coptic binding, there are multiple leads instead of just one. Each pair of adjacent holes represents one lead of thread. The needle goes in the first hole of the pair, jumps down to the other on the inside of the book, passes out and forms a lark's head around the stitch below it, then passes in and jumps back up to the first hole. From there it passes out and into the next signature, then repeats.

This forms one chain of herringbone stitches and one chain of simple stitches for each pair of holes. On the inside, doubled lengths of thread are visible with short gaps between them. (In a Coptic binding, the threads are not doubled and there are no gaps.)

The binding I worked with seemed quite sturdy; though it was about a hundred years old, none of the stitches had broken, though the glued backing was cracked into two sections. It was also quite easy to work with once I found the pattern. I was able to cut out the undesired group of pages, then tie in new lengths of thread on the four leads to sew the one loose signature onto the rest of the text block. I then covered the spine with glue, added super, and cased it in to a leather cover.