Bookbinding

Grain direction: the reason your notebook will not lie flat

A notebook that springs shut, pages that ripple after gluing, a cover board that curls within an hour of being covered: almost always the same fault, and the fault is grain. It is the piece of theory that separates books that behave from books that fight you.

What grain actually is

Paper is made from a slurry of water and cellulose fibre poured onto a moving wire mesh. As the water drains, the web of fibres forms while being carried in one direction, and long fibres in a moving fluid line up with the flow. They settle parallel to that direction, and the alignment survives pressing and drying. That is the grain.

Every machine-made paper and board therefore has a direction and behaves differently along it than across it: stiffer along the grain, more willing to fold along it, tearing more predictably along it. Cellulose fibres also swell far more in diameter than in length, so a sheet taking on moisture expands mostly across the grain and barely at all along it.

The rule

In bookbinding, the grain must run parallel to the spine. Not usually, not preferably: in every component. The text block, the endpapers, the cover boards and the covering material all have to agree, and they all have to agree with the spine.

There is nothing arbitrary about it. A book flexes at the spine, and paper flexes willingly along its grain. It also lives in a room where humidity rises and falls, and paper moves across its grain. Line the grain up with the spine and both facts work for you: pages turn easily, and seasonal movement runs harmlessly across the width.

What goes wrong when it is wrong

Pages cockle. Apply paste anywhere near a wrong-grain sheet, or let it sit through a humid week, and it expands across its width. Held at the spine, it cannot expand freely, so it buckles: the waves along the gutter that no amount of pressing permanently removes.

Boards warp. Gluing covering material to one face wets it, so the board expands on that side and curls. With the grain parallel to the spine, the curl bends the board across its width, which the inner lining counteracts. Get it wrong and the board bows along the spine axis, which nothing inside can pull straight.

The book resists opening. A cross-grain text block is asked to bend against its stiff direction every time it opens. It feels springy, will not stay open on a table, and snaps shut the moment you let go. Most people notice this fault first and blame the sewing.

Three ways to find the grain

The bend test

The everyday test, and the only one that leaves the sheet usable. Hold the sheet by two opposite edges and bow it gently towards yourself without creasing it, feeling how much it pushes back. Turn it ninety degrees and bow again. One direction gives noticeably less resistance: in that direction the fold line runs parallel to the grain. On thin papers the difference is subtle; on board it is unmistakable.

The tear test

Tear a strip from an offcut in one direction, then another at right angles. A tear running with the grain travels between the aligned fibres and comes away comparatively straight. A tear across the grain has to break fibres, so it wanders and feathers.

The moisture test

Cut a small square from an offcut, dampen one face with a sponge or a wet finger, and set it down. The wetted side expands, mostly across the grain, so the square curls into a shallow tube whose axis runs with the grain. It is the most definitive test and the most destructive, so keep it for a board that will not answer the bend test clearly.

Grain-long and grain-short

Paper is grain-long, or long grain, when the grain runs parallel to the longer edge, and grain-short, or short grain, when it runs parallel to the shorter edge. The same sheet size is sold both ways, which is why the terms exist.

Notation follows one of two conventions. Some suppliers underline the dimension running with the grain, so a sheet listed as 640 x 900 with the second figure underlined has its grain running the 900 mm way; others write the grain dimension last. Neither is universal, so confirm with a bend test.

Planning the cut

Work backwards from the spine. Decide the finished book's spine direction, then cut every component so its grain lies that way, remembering that folding halves a sheet and the fold becomes the spine. A folded signature is grain-correct when the grain runs along the fold, not across it.

Ordinary office A4 makes the point. Most cheap copy paper is cut grain-long, with the grain along the 297 mm edge, because printers feed more reliably that way. Fold it in half for an A5 book and the fold runs at right angles to the grain: exactly the arrangement that produces a springy, cockling notebook. Fold the same sheet the other way, long edges together, for a tall 105 x 297 mm book, and the fold runs along the grain. For a proper A5, buy grain-short A4 or cut from a larger parent sheet.

Board deserves the same attention. Greyboard has a pronounced grain; dense millboard has a weaker one, but still bend-test the offcut.

Folding, cracking and scoring

A fold along the grain separates fibres already lying parallel to the crease, so it goes down cleanly. A fold across the grain has to break every fibre it crosses, which is why cross-grain folds on heavy or coated stock crack into a ragged white line.

Scoring is the remedy where a cross-grain fold is unavoidable, usually on a cover. Run a bone folder firmly along the fold line against a straight edge, on the face that will end up on the outside of the fold. That crushes the fibres into a channel and pushes a raised bead out on the opposite face; fold so the bead sits on the inside, and the fold bends around a controlled line rather than tearing along a random one.

With the grain sorted, the next step is a book you can sew: the three-hole pamphlet stitch. The bookbinding box is in development, with grain-correct paper for the format it makes.