What the grain is
Paper is made of fibres suspended in water and drained onto a moving screen. Most of those fibres settle lying along the direction the screen was moving, the way floating logs align in a current. That alignment is the grain. Paper is not the same material in both directions: along the grain it is stiff and obedient; across the grain it resists, springs back, and wants to curl. It also grows and shrinks more across the grain than along it when humidity moves, which is why a whole book can warp from one careless cut.
A signature is folded before it is sewn, and the fold must run with the grain. Folded with the grain, a crease stays sharp and flat under the bone folder. Folded against it, the surface breaks — you can see the crackle in the fibre and hear it faintly — and the folded edge turns wavy. Sew that signature into a book and the waviness travels: the text block fans open, the spine rounds unevenly, and the case will rock on a flat shelf.
Three tests at the bench
None of these needs equipment, and none damages a sheet if it is done on an offcut or a corner you were going to trim.
The fold test
Fold the sheet halfway in one direction, crease it lightly, open it, and fold it the other way. The direction that folds easily, with a crisp crease and little spring-back, is with the grain. The direction that fights you and bulges at the crease is across it.
The tear test
Tear a small offcut from an edge, slowly. The tear runs with the grain: a tear that travels straight and long is following the fibres; one that wanders and steps sideways is crossing them.
The damp test
On a corner you can spare, lay a wet fingertip or a damp sponge on one face of the sheet and set it down for a minute. The paper curls, and the axis it curls around is across the grain — that is, the sheet curls so that the fold parallel to the curl's length runs with the grain. This test is the most reliable on stubborn stock, and the slowest.
| Test | How it is done | What it tells you |
|---|---|---|
| Fold | Fold both ways, crease lightly, compare the spring-back | The easy, crisp direction is with the grain |
| Tear | Tear a small offcut slowly from an edge | A straight, long-running tear follows the grain |
| Damp | Wet one corner of the sheet, wait a minute, watch the curl | The sheet curls across the grain; the flat axis is the grain |
Grain decides the whole book
In a case binding, the grain of the text block, the endpapers and the boards must all run the same way: head to tail, parallel to the spine. If the boards are cut across the grain, they will cup toward the pasted side as the paste dries, and the case will pull the book open or shut on its own. If the endpapers run the other way from the text, they fight the signatures at the joint every time the book is opened, and the hinge fails early — which is most of the broken books that arrive at this shop for repair.
Machine-made paper bought by the ream has a grain whether the label mentions it or not. Ream wrappers usually mark it — a number underlined, or the phrase "grain long" — and where a supplier cannot tell you, a fold test on the top sheet takes a minute. Handmade and mould-made sheets are the exception: their fibres lie every which way, which is part of why they behave so gently, and why they forgive a binder more.
The bench rule, entered in the ledger every time stock is cut: find the grain first, mark it with a light pencil line along the edge of the sheet, and never let a fold, a board or an endsheet cross it.
If you are binding at home
Test the grain before you cut anything to size, not after. Cut your text block first, find the grain in the offcuts, and then choose the board and endsheet stock to match. When in doubt, fold a spare corner: the sheet will tell you the truth every time, and it tells it before the knife, which is the only moment the answer is still useful.
Related shop practice: Shelves, light and humidity: keeping bound paper. For the tools and stock this shop keeps, see the work, and for questions about a particular sheet or book, write to the shop.