If you make your own notebooks or sketchbooks, or want to add some removable items to an artist’s book, today’s fold is the simplest way I know of to make a pair of pockets. Assuming your book to be a rectangle with the height greater than the width, you will need a square of paper with a diagonal measurement a bit more than twice the height of your book.
Place your paper in front of you with a point at the top. Fold the bottom point up to the top one and crease firmly. Now fold the left tip of the triangle over to the right tip. Crease the new fold firmly. When you open your paper flat, the crease pattern should look like this.
The next image shows what the folded paper looks like in relationship to the book block.
Place your paper diamond-wise again. (The crease from your first fold should lie horizontally.) Fold the top tip down so that the distance from the horizontal crease to the new upper folded edge is equal to the height of your signatures. Fold the bottom tip up so that the distance from the horizontal crease to the bottom fold is the height of your signatures. Fold the left point toward the middle so that the distance between the folded edge and the vertical crease is equal to the width of your signature. Repeat with the right point.
Re-fold the horizontal fold —bring the bottom edge up to the top one— then the vertical one. The picture below shows the folded pockets on top of the book block.
You have created two pockets: you can add the pockets anywhere in your book by sewing them in as a single signature, or you can add the pocket fold as the outside layer of a single signature book.
If you want twice as many pockets, you can make a smaller version of the pockets, and sew them in at the same time.
The smaller pockets can go either on the inside or the outside of the larger pockets. The image below shows them on the outside.
Tomorrow I will show you how to fold a single piece of paper to produce six pockets.