Folding and nesting signatures neatly

A signature, or section, is a group of folded sheets nested together and sewn through the fold. Almost every sewn book is built from them. It took me longer than I would like to admit to realise how much the quality of a finished book depends on folding them carefully. Here are the habits I have settled on.

How many sheets per signature

The number of sheets in a signature is a balance:

• Too few sheets, and the book has many sections, which means more sewing and a spine that can feel lumpy.
• Too many sheets, and each signature becomes thick. The inner pages stick out further than the outer ones at the fore-edge, and the fold resists closing.

For ordinary writing paper I use four sheets per signature, which gives sixteen pages. For thicker drawing paper I drop to three. For very thin paper I sometimes go up to six. If in doubt, fold a test signature and see how it feels.

Fold one sheet at a time

The single biggest improvement in my folding came from folding each sheet individually, rather than folding the whole stack at once. Folding a stack creates a rounded fold that never sits flat, and the outer sheets are stretched more than the inner ones.

I fold each sheet separately, crease it, and then nest them one inside another.

The fold itself

• Check the grain direction first. The fold should run with the grain.
• Line up the corners of the sheet carefully, holding them together with one hand.
• Press down at the centre of the fold with the other hand, then slide the bone folder from the centre to each end.
• Finish by running the flat side of the folder along the fold once more, firmly, with a scrap of paper on top to avoid shiny marks.

Keeping everything square

Even with careful folding, sheets end up a millimetre or two out of line. To square up a signature, I hold it loosely by the spine fold and tap the top edge gently on the table. Then I tap the fold itself, so everything settles into place.

I stack finished signatures with their folds alternating direction, then put a board and a heavy book on top. Leaving them pressed overnight before sewing makes them noticeably crisper and easier to handle.

Marking the order

When I fold a large batch, I make a small pencil mark on the spine fold of each signature, in a slanting line across the whole stack. If the signatures ever get shuffled, the diagonal line tells me the correct order at a glance. It is an old trick and very handy.

Trimming afterwards

Thicker signatures will have a stepped fore-edge, with the innermost pages sticking out furthest. Some binders trim the whole text block after sewing with a guillotine. I do not have one, so I either trim each signature with a ruler and knife before sewing or simply leave the edge as it is. A slightly uneven, deckled edge suits a handmade book well.

The payoff

Neatly folded signatures make sewing easier, help the book open well and give a much tidier spine. It is a quiet, repetitive task, and I have come to enjoy it as a way of settling into a project: an evening of folding, with music on, before the real binding begins.