Paper, Board and Binding Fundamentals: Grain, Weight and Structure
Domain 2 tests paper and board properties and the arithmetic that turns a flat sheet into a book block: grain, weight, calliper and spine width.
Paper and board properties
- GSM is weight in grams per square metre; calliper is thickness in millimetres. Two papers of equal gsm can differ in calliper because of bulk, so never use gsm as a thickness.
- Grain is the direction the fibres lie. Fold along the grain, and keep grain parallel to the spine so the book opens freely and the covers stay flat.
- Grain tests – tear test (tears straighter along the grain), fold test, float test (the curl tells you the cross-grain).
- Sizing and pH – sized paper resists water-based adhesive; acid-free paper is pH 7–8.5 with an alkaline reserve for long life.
- Board grain likewise runs parallel to the spine. Boards should square 3 mm beyond the block at head, tail and fore-edge.
Sheet to block
One A4 sheet folded once gives four A5 pages. Pages ÷ 2 = leaves.
Worked example. A book has 160 pages on 80 gsm paper, bulk 1.2, boards 2 mm. Leaf thickness = (80 × 1.2) ÷ 1000 = 0.096 mm, about 0.1 mm. Leaves = 80, so the block is 8 mm. Add two boards (4 mm) and 3 mm cover allowance: spine width 15 mm.
Traps
- Measuring the spine on a rounded, closed book instead of a pressed block.
- Forgetting board thickness when cutting the cover.
- Grain running across the spine: wavy pages, warped boards, cracked folds.
- Ignoring bulk when ordering paper for a fixed spine.
- Working from page count instead of leaf count.