Print finishing / Binding
Perfect binding, the spine width, and the page that will not open
Sheets glued at a flat spine rather than folded, which gives a printable spine and a document that opens less flat than a stapled one.
What is physically going on
Perfect binding trims the folded edge off and glues the resulting flat stack into a cover. Two things follow. The spine has a width, which is a function of the page count and how bulky the paper is, so it is a measurement that cannot be known until both are fixed, and it is the measurement a cover design needs. And the pages are held along their entire inner edge rather than at a fold, so the document resists opening flat, more so as it gets thicker. That makes the gutter requirement larger than for a stapled document, and it makes anything spanning the spine a bad idea, because the part nearest the glue is the part that will not be seen.
The decisions
Reasons rather than a description of the code. Where a number depends on the stock or the press, the instruction is to get it from the printer rather than to quote one here, because spine width, creep and bulk are not constants.
- Get the spine width from the printer once the page count and the stock are fixed. It depends on paper bulk, which is a property of the specific stock rather than of its weight alone.
- Design the cover as one piece across front, spine and back, with the spine width as a measurement rather than a guess, and expect to redo it if the extent changes.
- Allow a larger gutter than a stapled document of the same extent, because the binding holds the whole inner edge rather than a fold.
- Do not run an image or a rule across the spine on inner pages. The middle of it disappears into the binding and what is left does not line up.
- Keep spine text clear of the edges by a comfortable margin, since the position of the spine relative to the trim moves slightly.
- Only put text on the spine if the document is thick enough to carry it legibly, which is a threshold the printer will tell you.
What it means for the page rule
The page rule is the part of this a document author controls. The binder decides the gutter and the printer decides the creep allowance; the document's job is to leave the room those decisions need.
/* The inner pages: a larger gutter than a stapled document needs,
because a glued spine resists opening flat. */
@page :left { margin-right: 34mm; }
@page :right { margin-left: 34mm; }
/* The cover is a separate page whose width includes the spine, so it is
a different page size rather than a variation on the inner one. The
spine measurement comes from the printer once extent and stock are
fixed. */
@page cover-wrap {
/* front + spine + back, plus bleed on all four edges */
size: 437mm 303mm; /* example only: measure yours, do not copy this */
margin: 0;
}
.cover-wrap { page: cover-wrap; break-after: page; }
/* Nothing important spans the spine on an inner page: the middle of it
is in the glue. */What people do instead
Designing the cover before the extent is final. The spine width changes with the page count, so a cover laid out against an estimated extent has the spine text and the front-to-spine fold in the wrong places, and the whole cover has to be redrawn rather than adjusted.
How to find out rather than assume
Ask the printer for the spine width in writing once the extent is fixed, and lay the cover out against that number. Then open a bound sample at the first page and the last and see how much of the inner margin is actually readable.
Where this API sits in it
Outside it. This API renders HTML to PDF: it produces a sequence of pages at the size and margins your CSS and the render options set, and everything on this page happens afterwards, to paper, in a bindery. There is no imposition option, no binding option and no finishing option, and there could not be, because none of those are properties of a file. What the render does decide is the two things finishing cares about most: how many pages there are, and how much room is left at the edges. Both of those are set before anything is printed, which is why a finishing constraint discovered late is expensive and one designed for is free.
Frequently asked
Can the API impose the pages into printer spreads?
No, and you should not want it to. Imposition is done by the printer with tooling built for it, against the specific press, stock and folding scheme, and the input that tooling wants is single pages in reading order, which is what a render naturally produces. Supplying anything else means somebody has to undo it first.
How do I get the page count to a multiple of four?
By deciding where the padding goes rather than letting it land at the end. Add the blanks deliberately, style them with the blank page rule so they carry no folio or running header, and mark them as intentionally blank if the document is formal. Counting the covers into the total is the step people miss.
Do any of these apply to a document that is only ever read on screen?
No. This cluster is about physical operations on paper, so if a document is genuinely never printed, none of it is your problem. It is worth checking that assumption rather than making it: delivery notes, permits, method statements and invoices all end up on paper more often than the people generating them expect.
Related finishing topics
The operations that constrain each other, then the rest of the same group.
The inner margin a bound document needs and the outer one it does not
The extra width on the bound edge, which exists because a fastened document does not open flat and the innermost part of the page curves away from the reader.
Why a stapled booklet has to have a page count divisible by four
A booklet made by folding sheets and stapling through the spine, where every sheet carries four pages and the arithmetic is therefore not optional.
Supplying single pages, and letting the printer impose them
The rearrangement of pages into the order they have to be printed on a sheet, which is the printer's job and is made harder by supplying pages already paired.
page (named pages) in paged output
The property that expresses this in the page rule.
Every finishing topic
The full list, grouped by binding, folding and trimming, and collation.
None of this is a render option, and none of it could be. What the render controls is that the page count and the margins are the ones the finishing needs.