Place the thin leather on a table with the outside surface downward. Place the book on top of the leather. Measure the outside border of the book. Draw an outline of the book onto the leather, including the front, back and spine.
Measure the top to the bottom of the book and add an extra inch to the measurement. Measure the width of the book and multiply by two. Add an additional inch to this measurement, along with the measurement of the book's spine. Trace the line measured. There should now be an outline of the book on the leather, along with a 1/2-inch border all the way around the outline of the book.
Cut out the outline. Lay the leather out flat. Locate the center of the leather and mark where the spine of the book will be. Mark it with a pencil.
Apply glue to the plastic backbone and place it where the markings are made. Turn the leather around and rub the backbone through the leather until the glue has dried. Flip the leather again, so the backside is facing upward.
Apply glue to the front side of the leather binding, keeping the glue inside the lines. The glue should not cross the lines into the border. Place the book on the glued part and slightly press down.
Glue the backside of the leather binding. Fold the book so the leather binding fits with the backside, automatically hugging the spine. Press down on the book until both sides with glue have dried. The spine should not be glued to the leather.
Cut each corner of the leather at a 45-degree angle. Make the cut in the border section so the borders can fold inward without overlapping each other.
Apply glue to the top border of the book and fold it down so it hugs the outline of the book. The glue should be on the inside of the book. Open the book widely so the spine separates from the leather binding. Fold the border down so it is inside the book. Push the fold into the book's spine with a small screwdriver. Repeat this step for the bottom border, including the spine trick.
Apply glue to the side borders and fold the corners. Fold the sides inward so they are glued to the inside of the book. Make sure the corners are folded so they do not overlap or are left incomplete.
Place the book somewhere dry and under a heavy weight. If the book is not placed in a press, the borders might curl, ruining the overall look. Once the glue has dried, the book is ready for use.