27 Aug
16 page signature front and back diagram

What is a signature in printing?

In the printing world, a signature isn't only a scribbled name on a formal document. 

When offset printing books, we create a large sheet of paper to print at least four pages on each side. Using them decreases paper waste and increases efficiency by lowering the number of aluminum plates that must be created.

The flat signature layout can look confusing at first, but it folds neatly into proper page order. For long books, many signatures are created and bound together.

Positioning pages on a signature is called imposing. Creating a properly imposed signature is necessary for a book to come out in the proper order. One page being misoriented or out of place would require a complete reprint of the whole thing. The most common impositions have 4, 8, 16, 32, or 64 pages on them. Having numbers divisible by four simplifies the folding process. Signatures also allow for easy organization of spreads, two facing pages, after printing is complete.

Once the signatures complete their printing and folding, they are moved into our bindery. The pages are trimmed and bound there.

Signature imposition changes with the type of binding.

On saddle stitch books the signatures are nested inside one another and then stapled down the middle. To help this, the first and last pages are printed together, the second to last is printed with the second page, and so forth.

It is different for perfect bound books since the signatures are stacked on top of one another instead of being nested. The spine of the signatures goes through the “grinder” which creates a rough edge. This increases the surface area and depth that the glue used for binding can stick to. The signatures are then stacked on top of one another and glued together. The cover is a separate sheet of paper that wraps around them and holds them in place.

For coil-bound books, the signatures are still stacked on top of one another. The stack is then trimmed, and holes drilled or punched into it for the spiral.

The following diagrams show how a 16-page saddle stitch book is imposed and folded.






Saddle Stitch Signatures being nested into one another:



Perfect bound signatures being stacked on top of one another: