Skip to 0 minutes and 3 secondsAs you were learning about the process of rebinding earlier, some of you may have been surprised to hear that testuyōsō-style books, which have writing on both sides of the page , were rebound as scrolls , which usually have writing only on one side. You cannot simply cut the pages, line them up next to each other, and paste them together, so how do you do it? The answer is that sheets of washi paper can be split into layers to effectively make two sheets out of one. What you do is loosen the edge of the leaf like this. I have tried it myself to see how it works.
Skip to 1 minute and 19 secondsInsert your nail in the narrow gap and slowly run it along the edge, then, a paper will be peeled off into two pieces. You then gently pull apart to separate them. This is what it looks like now. In this case, I have left the layers partially connected to show that they are from a single sheet. Once this preliminary process is completed, the margins of each page are removed because they are no longer needed, the sheets are placed in sequence horizontally and pasted together. Thus, a scroll can be made from a tetsuyōsō book. The process of splitting paper into separate layers is known as aihagi or aihegi.
Skip to 2 minutes and 25 secondsNext, let us look at the opposite case, namely the conversion from “pouch” binding (fukurotoji) to tetsuyōsō or multi-section binding. In fukurotoji books, the writing is only on one side of the leaf whereas in tetsuyōsō books  it is on both, so quite a bit of work is required to change from one to the other. First, the fukurotoji book is taken apart. This is a leaf from a fukurotoji book. You first spread it open like so. As you can see, it is fairly simple to make a scroll by connecting the spread out leaves horizontally, although, of course, the margins first have to be removed (a scroll has no "pages" as such).
Skip to 3 minutes and 13 secondsTo rebind it as a tetsuyōsō, however, the leaves first have to be cut along the middle crease. If you remember the characteristic of tetsuyōsō binding, the text "skips" between right side and left side of the leaf except for one leaf (the bottom leaf of each small "fascicle"). So if you are not very careful when you repaginate the book, the text becomes unreadable. Having carefully determined in what order to arrange the portions of text and cut them accordingly this is a copy I have made for illustration purposes, you then proceed to paste them onto a thin sheet of white paper like so. The red marks here show where the original binding holes were.
Skip to 4 minutes and 50 secondsAs we saw earlier, you position the portions of text on the new sheet so that the binding holes appear on the outer edge. The process is then repeated on the back side, also making sure that the binding marks are on the outer edge. The result is a triple-layered sheet, which is then stacked on other sheets and bound normally as a tetsuyōsō. Some of you may be wondering why making the holes so visible In a standard tetsuyōsō book there are generous margins on both sides of the text, If you put pages on the other side of the paper (which is rather straight forward), It does not look right as the margins are too narrow.
Skip to 5 minutes and 58 secondsso in order to make the rebound book look as much as possible like a “real” tetsuyōsō book the portion of the page with the holes has to be included. By the way, this is also the part of the page that tends to get dirtier as one turns the pages. To sum up, converting from fukurotoji to tetsuyōsō is extremely laborious, and the fact that people were prepared to go to such lengths to do it is something that we as researchers need to consider very carefully.
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