1. What Do the Stacks of Folded Paper on a Book's Spine Show?
If you stand a book up and look at its spine, you may see several stacks of folded paper piled together [2]. These bundles are called oricho (signatures), and they are the basic unit used when making a book.
When you print multiple pages on the front and back of a large sheet and fold it in a specific order, you create an oricho. If you fold it into four parts, you get 8 pages; if you fold it into eight parts, you get 16 pages [2]. This calculation comes from folding the paper in half three times to make 8 faces, and counting both sides gives 16 pages.
However, 16 pages is just an example for an eight-fold signature. Not all books are made in 16-page units. So, what order are those 16 pages arranged in on the paper?
2. Why Pages Cannot Simply Be Laid in Order After Folding
Paper for printing is used by cutting or folding it in half. When you fold a full sheet of A-size or B-size paper, you create signatures that hold multiple pages [3].
To ensure the pages appear in the correct order after the paper is folded, you must decide how to place them on the large sheet beforehand. If you simply arrange page 1, page 2, and so on from left to right, the order will be wrong once the paper is folded. This process of arranging the layout is called "imposition" (or *menzuke*).
Imposition changes depending on how the book is bound [3]. Whether the pages inside a signature line up correctly depends on the binding method chosen for that specific book.
Yet, even if the folding and imposition are correct, some books still open poorly. The reason lies within the paper itself.
3. How Paper Fiber Direction Affects How Easily a Book Opens
Paper is made by filtering a mixture of pulp and water to create layers of fibers, then compressing them to remove water and drying them. The machine that makes paper has a wire section, a press section, and a drying section [5]. These machines are said to have originated from the long-wire papermaking machine invented by Robert in France in 1798 and put into practical use in Britain in 1808.
When this machine makes paper, the fibers align in the direction of the flow [3]. Because of this, paper has a "long grain" and a "cross grain." Long grain means the fiber direction matches the longer side of the sheet.
Books are made so that the spine and the direction of the paper fibers (the grain) are parallel. If they are not aligned, it is said that the pages will be hard to open and the edges may wave [3]. Materials on library binding also state that books are made with the grain running vertically so that turning pages along the grain makes them easier to read [4].
You can see the grain direction by tearing paper. Paper tears easily in the long-grain direction (along the fibers) and is harder to tear in the cross-grain direction (against the fibers) [3].
4. Why Proofreading Is Repeated Many Times Before Printing
Before printing begins, proofreading is done to find and fix errors in text. The first check is called the "first proof" (or *shoko*), the second is the "second proof" (or *saiko*). Once necessary corrections are confirmed and it is judged ready for printing, it becomes "final approval" (or *korryo*). For books, it is generally said that three rounds of proofreading lead to final approval [6].
As an example of the time involved, one publisher's self-publishing service flow involves organizing the manuscript and layout, then sending it to the printer. The first and second proofs are done by professional proofreaders and the author until final approval. After that, plate making, printing, and binding follow. It is said that about 4 to 5 months pass from submission to completion [7]. Completed books are also sent to the National Diet Library.
This 4 to 5 month period is just one example of a self-publishing service. Other books may not take the same amount of time.
5. The Three Stages of Printing After Approval
Printing is divided into three main stages [1]. The first is "prepress," where manuscript layout, typesetting, and plate making are done to create the original plates for printing. The second is "press," which is the actual printing stage. The third is "postpress," which includes finishing tasks like binding and gloss coating.
In the stage of making plates, there is a method called CTP (Computer-to-Plate) that creates plates directly from data without using film. It began being used in Japan around 1995 (Heisei 7). Because it reduces steps and shortens time, this method is now the most commonly used in offset printing [8]. As the word "around" suggests, not all companies switched at the exact same time.
The printed paper is folded into signatures and enters the final binding stage.
6. Binding Signatures: Sewing with Thread vs. Gluing
Binding means joining printed materials or manuscripts together to make one book [10]. One type of binding is "thread sewing" (or *itokagari*), where signatures are sewn together with thread. It is strong and opens easily, but the cost is higher [9].
Another type is "perfect binding" (or *musentoji*), which does not use thread or wire but hardens the spine with adhesive. It is cheaper to make, but it is said to be less strong and pages may fall out more easily [9].
Hardcover books (or *joseihon*) are made by wrapping the contents in a separately prepared cover. This creates a "tuck" where the cover extends beyond the text block. Paperback books (or *namiseihon*) wrap the contents in the cover and then trim all three sides, so there is no tuck [10].
7. How to Check Paper Grain with Items on Your Home Bookshelf
You can find the paper grain by tearing paper. Make cuts of the same length in the same spot on newspaper or unused copy paper, then tear in one direction. Next, rotate the paper 90 degrees and make a cut of the same length from the same spot, tearing it similarly to compare. The long-grain direction tends to tear more easily. Please tear slowly so you do not cut your hands on the edges.
Open a book gently near the middle and look at the center. Some books show visible thread. If you cannot see thread, it may be bound with adhesive. Do not force the book open, as this can damage it.
If you want to study further, explanations of paper grain, folding, and binding are summarized with diagrams by the Japan Federation of Printing Industries (Source [3]) and in the National Diet Library's binding guide (Source [9]). Comparing your own books by looking at the spine, edges, and how they open will help connect these explanations to real objects.