The Fold Test: Finding the Grain of a Sheet

Grain runs in the direction the stock travelled on the paper machine, and almost everything a binder does with a sheet depends on knowing which way it lies. Fold with the grain and the fold is clean; fold across it and the fold cracks through the coating or the fibre. Sew a text block with the grain across the spine and the leaves fight the opening for the life of the book. There is no marking on a ream that reliably tells you, so the bench tests the sheet.

How the fold test is done

Take a spare sheet of the same stock, square and uncreased. Fold it in half one way and press the fold with a bone folder, then open it and fold it the other way and press that fold. Compare the two fold lines against a light. The fold that is smooth, and that lets the two halves fall together without resistance, runs with the grain. The fold that feels stiffer and shows a roughened or slightly cracked line runs across it.

The second reading is the hang test. Cut two strips about 50 mm by 200 mm, one cut along each suspected direction, and hold them by one end over the edge of the bench. The strip that bends over further, and stays bent, is the one whose length runs across the grain; the strip that stays straighter has its grain along its length. On a heavy board the hang test is more reliable than the fold.

Does the fold test work on coated and laid papers?

On a coated sheet the test still works, but it is read on the coating. Across the grain, the coating cracks at the fold and shows a fine white line; with the grain it does not. Handle the sheet by the edges, because a thumb crease in the wrong place will read as a grain crack and send the test the wrong way.

On a laid or a watermarked sheet the laid lines run parallel to the grain in most papers made on a Fourdrinier wire, so the test can be confirmed by eye: the chain lines cross the grain. On a handmade sheet formed on a mould, the laid lines run across the grain of the mould, so the eye reading is the reverse and the fold test settles it. Where a sheet is so heavy that it will not fold cleanly at all, the hang test and the tear test are the ones to use: a sheet tears more easily along the grain than across it.

Why the spine follows the grain

A book is sewn and glued along its spine, and the leaves bend there every time it is opened. If the grain runs across the spine, every leaf is bent against its own fibre direction, and the block opens stiffly, springs closed, and eventually breaks at the fold. If the grain runs parallel to the spine, the leaf bends with the fibre, and the book opens easily and stays open.

The rule holds for the case as well. Board for the covers is cut with the grain running vertically, in the same direction as the spine, so the boards do not warp with changes in humidity. A board cut across the grain will bow away from the block in a dry room and cup towards it in a damp one, and no amount of pressing will keep it flat.

What happens when the grain is wrong

Short of reprinting, a binder has three moves: bind the block so that the grain runs correctly and accept a slightly different trim, bind it against the grain and accept a stiff opening, or break the grain deliberately at the spine before sewing. The last is done by running a bone folder along the fold line of each section to soften the fibre. It improves the opening and it weakens the paper along that line, which is the trade it makes.

For a run already printed and cut with the grain the wrong way, the practical answer is a binding method that does not depend on the leaf folding at the spine: a stitched or a wire binding where the page turns around a wire rather than bending at a fold. That is why so many reports printed on a low grade stock end up in a wire binding, whatever the designer intended.

Write the grain into the specification

Grain direction belongs in the paper specification next to the grammage and the caliper, named as long grain or short grain against the finished size. On a run of any size, ask for a sample of the actual making, not of the paper grade in general: the same grade supplied by a different mill can be a different way round, and the fold test on the delivered stock is the only reading that describes the job in front of you.

Sources consulted for this folio: ISO 536 on the determination of grammage, ISO 534 on thickness, density and specific volume, and ISO 1974 on the tear resistance of paper.