Grain direction decides whether a book opens flat, permanently
Finding the grain
Tear a scrap both ways. It tears straight along the grain and raggedly across it. Do this once per batch and note it.
Which way
Grain must run parallel to the spine, head to tail. Every sheet, the boards, and the cover material all follow the same rule.
Why it matters
Against the grain, the folds resist and the book springs shut. There is no way to fix it afterwards short of rebinding.
