Thanks to Cambridge's Bob Groser, I'm able to offer an inside look at how a Bible's book block is assembled and prepped for "casing in" (i.e., for having the cover attached). Bob provided a trio of book blocks in various stages of completion and stepped me through the process. The Bible in question is the Clarion ESV, but the process illustrated is common to quality Bibles.
1. THE LOOSE SIGNATURES
The Clarion is printed on a Timson web press "specially configured for accurate lightweight printing." An interesting geographical note: while the sheets are printed in the Netherlands, the Timson is actually manufactured about fifty miles from Cambridge in Northampton, which is also the manufacturing center for English shoemaking.
After printing, the sheets are folded into signatures -- in this case, 80 pages per booklet, which works out to twenty folded sheets. The tick marks on the spines of each signature are designed to ensure proper order. They're numbered -- twenty-six, not counting the maps -- and the marks form a diagonal line for easy visual confirmation.
If the Kingdom of God is already and not yet, the same might be said for this Bible. Holding the loose signatures tightly at the spine, you can flip through it and envision the finished book it will become. At the same time, the pages are untrimmed, which means the front edge hasn't always been separated. There are grayscale guides along the bottom and, of course, the whole thing is easier to part than the Nile River.
The signatures are Smyth-sewn together. The trick is to do this loosely. As I learned in my bookbinding class, when a book block is bound too tightly, the pages don't open as easily as they ought. Before binding, a sewn text block will show gaps between the signatures when opened, the stitches clearly visible. The process of binding tightens things up a bit and closes those gaps.
Note that these blocks are machine-stitched. The result is a little different in appearance from hand-stitching. The former looks stronger to me -- perhaps because there are so many more holes! I've hand stitched books together, punching six to eight holes in each signature. With the machine there seem to be more points of connection. Someone with more knowledge of both processes would have to say whether one is stronger than the other. Suffice to say, Smyth-sewn bindings are very good.
Endpapers are sewn on, too, while the endsheets are "tipped on" -- i.e., they are glued. Cambridge typically uses imitation leather endsheets. In a paste-off edition, which is the traditional method, the text block is connected to the cover by pasting the endsheets down onto the back of the cover.
At this point, the book block feels very much like a book. There are still some details missing, however. The bare spine will have to be prepped before the cover can be attached. The three edges will need trimming before they can be gilded. And we'll need decorative headbands and some ribbon to finish the look.
3. THE FINISHED BOOK BLOCK (READY FOR CASING IN)
There are two types of binding common on Cambridge Bibles, the traditional paste-off edition mentioned earlier and the more labor intensive edge-lined edition. The text block illustrated here is prepped for a paste-off binding -- specifically, the brown calfskin cover. Hence the brown ribbons and the brown-and-gold headbands.
First, the sewn book block is compressed prior to gluing -- "a rather alarming and noisy process," according to Bob. In the parlance of binding, the text block is said to have been "nipped" or "smashed." Now that the signatures are nice and snug, glue is applied and the book block is rounded, which gives the spine a gentle curve. Then it's ready to be backed. Backing consists of applying a thin layer of glue, then wrapping the spine in a net-like wrap called mull. This strengthens the spine, in particular the bond between the block and its endsheets.
"Three passes through the gilding machine (one for each side) then round cornered trimming and corner gilding with gold metallic foil (occasionally real gold is also used) followed by the art gilding process to give the 'red-under-gold' effect if required."
Somehow, I'd always imagined three swipes and you're done. Rounding the corners and re-gilding them came as a surprise. I also thought of gold gilding and art-gilding as two completely different processes, so the workflow interests me quite a bit.
Applying ribbons is quite simple: they are positioned by hand then affixed with glue. The decorative headband goes on top, giving both ends of the book block a finished look. In the old days, headbands were sewn by hand, but now the near-universal practice is to use pre-made ones, even in handbound books. A wide varity of colors are available.
For those of you interested in Bible hacks, such as adding additional ribbons, the photos above help illustrate the cleanest way to achieve a result. The easy method is to slip the ribbons down the spine and glue them in place, but this results in them traveling over the headband, which doesn't look correct. Ideally, you would need to use a tool to separate the headband from the book block, then pass your additional ribbons through the gap, pasting the headband back in place when you're done. It's much trickier, but results in a better outcome.
Now we have a book block ready to be cased in. In every respect but one, this is a finished product. In fact, I have used it in its unbound state on a number of occasions for reading. Trust me, no cover at all is the limpest binding you can imagine. (Sadly, you do end up fraying the backing, as you can see in some of the photos above.)
I'd like to offer special thanks to Bob Groser for the time he invested in illuminating the process. Needless to say, any errors in the recounting are mine alone.