How a book is made

Everything starts with a file. It holds the laid-out pages, the images, the fonts and a colour profile: a description of how the colours on screen should turn into ink on paper. Before anything is printed, the file is checked carefully, because problems are cheap to fix now and expensive later. The checks look for images with too little resolution, which would print blurry; fonts that aren’t embedded, which the printer can’t reproduce; text too close to the edge, which could be cut off when the book is trimmed; and colours that ink simply can’t reach. Only a file that passes moves on.

A book isn’t printed page by page. Many pages are printed together on one large sheet, arranged in a pattern called imposition. Some pages end up upside down and others side by side in a strange order, because the layout only makes sense once the sheet is folded. To be sure nothing is out of place, a quick first proof is printed and checked: every page in the right position and the right way up. Then comes a colour proof, printed to show as faithfully as possible how the inks will look on paper. Once it is approved, it becomes the reference the printer will match during the run.

Offset printing doesn’t print an image in one go. It splits it into the inks it will be printed with, and most colour images are built from just four: cyan, magenta, yellow and black. Each ink needs its own plate, a thin sheet of metal onto which its share of the image is transferred straight from the file. The areas that should print attract ink and the rest repel it, thanks to the simple fact that oil and water don’t mix. On the press, each plate is wrapped tightly around a cylinder and clamped in place.

In offset printing, the plate never touches the paper. It passes the ink to a cylinder covered with a rubber blanket, and the blanket passes it to the sheet. That indirect step is what gives the technique its name, and the soft rubber lets the ink settle evenly even on slightly textured paper. The sheet travels through one printing unit per ink, and the colours build up as tiny overlapping dots that the eye blends into a full image. Throughout the run, a strip of colour patches printed along the edge of the sheet is measured, so every sheet stays as close as possible to the approved proof.

The printed sheets are much larger than the book, because printing many pages at once is far more efficient. Before they can be folded, the sheets are stacked and taken to a guillotine: a cutter with a heavy blade that slices through a whole stack in a single, precise stroke. Each large sheet becomes several smaller ones, and each of those will turn into one section of the book.

Each of those smaller sheets is folded, usually two or three times, until it becomes a signature: a small booklet of consecutive pages. This is where the imposition pays off. Pages that looked scattered on the flat sheet now fall into reading order, the right way up. A small black mark is printed on the fold of each signature, in a slightly different position on each one. It looks insignificant, but it plays an important role in the next step.

The signatures are now collected in order, one on top of the other, to form the book block. This is when those little marks on the folds come into play. Each signature carries its mark a little lower than the one before, so together they form a neat diagonal staircase along the spine. If a signature is missing, repeated or in the wrong place, the staircase breaks, and the mistake can be spotted at a glance before the book is bound.

Some books are sewn. A thread runs through the fold of each signature, along the spine, and a small stitch at the head and the tail links it to the signature before, so the whole block is held together by thread. Sewing takes longer than gluing alone, but it pays off: a sewn book opens more easily, lies flatter and holds together for many more years of reading. That’s why it is often chosen for books that are meant to last.

Glue holds the block together and will also hold the cover in place. If the book isn’t sewn, a thin layer of the spine is milled away first, cutting through the folds so that every single page has an edge exposed to the glue. That is what lets a glued book hold its pages without any thread. Then a roller runs along the whole spine and coats it with an even layer of glue. From this moment on, the separate signatures behave as a single block.

The cover is printed on thicker paper and creased where it will bend, so it folds cleanly instead of cracking. It is placed against the glued spine, pressed firmly so the two bond, and then folded over the front and back of the block. Finally, the three open edges are trimmed. The cut makes them perfectly flush and opens the folded edges of the signatures, so the pages can turn. The book is finished.

A finished book is more delicate than it looks: corners dent and covers scuff. So books are packed into cardboard boxes chosen to hold them snugly, with no room to slide or rub against each other. Each box is filled, its flaps are folded shut and it is sealed with tape, ready to be handled many times on its way out.

The boxes are then stacked on a pallet, the wooden platform that forklifts and lorries are designed to move. They go on layer by layer, in an interlocking pattern like bricks in a wall, so the load doesn’t lean or shift. Once it is complete, the whole stack is wrapped or strapped so it travels as one solid piece.

Finally, the pallet is lifted onto a lorry and leaves the printing works. It goes to the publisher’s warehouse or to a distributor, who sends the books on to bookshops and libraries. From there, each copy sets off on a journey of its own.