Updated: Apr 16, 2019
The first hints of the Australian summer have appeared. In this season the care of full leather bound books is important.
I recently left a leather bound book in a car, in the sun, on a mid-30's day. It didn't like it very much. Overall, integrity of the binding held well, but the warping of the covers was still an issue. These severe conditions can bring to the fore some problems that librarians and conservationists have been dealing with for generations.
When exposed to moisture and heat, materials can expand and they can shrink. Sometimes, this can result in unbalanced forces being applied, and warping of a book's structure. During binding the outside surface of book-boards have leather or book-cloth glued onto them. At first, the boards soak up the moisture, then the moisture breaths out, and a bit of shrinkage occurs. This would pull the the boards into a convex shape. However, binders counter this but with an equal force to the other side, by gluing a layer of paper on the inside surface of the boards. The end papers are then also glued down on the inside surface. Usually, this results in a very slight concave shape, which may dissipate as the book is continually handled
The boards themselves have a structure that likes to be flat. Warping means that a significant force is being applied. I have sometimes found that fairly stable boards, with balanced force on either side, might warp a little bit, but over time as temperatures change and moisture is breathed in and out according the the atmosphere's humidity, the boards are able to return to their original, flat shape. I have seen oak boards take days to come flat again after gluing, but then remain stable for years. Each material is a little different. Some are are good at keeping flat, others good at returning to their shape, and some materials tend to exert a lot of the force that leads to these issues.
Leather is a material that can exert a lot of force. The leather binding left in the car was getting hot, changing shape, and the board warped accordingly. The outside surfaces of the book will always feel the severe conditions first, resulting in uneven pulling forces. The best way to countermand this is to re-balance the forces, and then encourage the boards to return to their flat configuration. Preferably this can be done throughout gentle changes in humidity and temperature, so the materials can 'breathe into' their flat configuration. For leather books, one method is to re-hydrate the leather, and let the book 'reset' into it's original shape.
What to Do When the Boards Warp
I am happy to supply appropriate leather conditioner and assistance to anyone with a Pilgrim. Just get in touch to let me know.
Begin by undoing the closure tie around the centre of the book, if it has one. These ties are practical for travel, but they are still a force vector on the book and you will want to give the covers a break from that.
Then, use a small amount of tallow-based leather conditioner, applied with a clean cotton cloth, to re-hydrate the outer surface of the leather. Apply several light layers to help the leather slowly drink it in, being careful to cover all of the surface without getting it on the pages. You may want to use a lose sheet of paper as a shield to help with this.
Leave the book for about twenty minutes and then buff off any excess conditioner.
Position a clean sheet of paper on either side of the book, place it on a flat surface (like a table), and rest under gentle weight over-night. I use old national geographic magazines, and find that about four or five of these is appropriate. If available, a few flat layers of cloth placed on either side of the book while it is weighted is ideal.
Handle the book, open it and close it. Let any changes in shape work themselves into the binding. If possible, let it rest under gentle weight for another night.