One of my goals as a Lennox Foundation intern was to learn more about leather repair and, as an exercise, I’ve been dyeing and paring leather over the past couple of weeks for two leather rebacks done on library discards.
Before I was able to do anything with the leather, I had to learn a thing or two about paring knives and how to properly sharpen them. I started by reading Leonard Lee’s Complete Guide to Sharpening to get a better idea of the process. This book was extremely helpful by not only providing diagrams and explaining the action at the molecular level, but by illustrating it with scanning electron microscopy. Back in April, Melissa wrote about the lab’s recent acquisition of a Tormek T-7 grinding system (you can read that post here) and we recently had the opportunity to fire it up.
One of the handiest features of the Tormek is that the wheel is water-cooled. This is important because metal tools are created with a specific balance of hardness and ductility; if the steel is too ductile it won’t hold an edge, but if the steel is too hard it will crack when force is applied. During the manufacturing process, the specific properties of tool steel are determined by controlled heating and cooling (i.e. tempering). When sharpening the tool on a wheel, the friction that results from placing a thin piece of metal on a spinning stone creates a lot of heat. The very thin cutting edge of a blade, when put under those conditions, will change temperature much more rapidly than the rest of the tool. This fluctuation can change the arrangement of carbon molecules within the metal, altering the properties of the tool’s edge. In this case, introducing water to the process dissipates the heat and preserves the original physical properties intended for the blade.
An added benefit of the wet-grinding Tormek system is that sparks do not go flying about when you are working at the machine. A few small rare earth magnets on the side of the water tray also conveniently collect all of the material that is taken off of the tool.
I was pretty surprised at the amount of material that was collected in the end – when I was taking down the machine to clean it at the end of the day, it looked like a little sea urchin was starting to grow inside.
I had brought an extremely dull and expendable English-style paring knife with me to Iowa for sharpening practice. When used on leather, this blade just kind of pushed the material around instead of cutting.
Using an adjustable measuring device and a flat jig, we set the Tormek up to grind at a 13 degree angle. White painter’s tape was applied to the knife handle as a guide for consistent placement.
I admit that the process is not as easy as it looks. After the first couple attempts, I ended up with a couple of different curvy planes at various angles along the edge of the knife.
But with some practice and adjustments to the way that I was holding the tool, I managed to form a consistent edge. After refining it by hand on a series of aluminum plates covered in finer and finer 3M Microfinishing film (from Jeff Peachey), I honed the edge with a strop and chromium oxide honing compound. The result is a fully functioning paring knife!
Completing these leather rebacks has made me appreciate anew the breadth and depth of knowledge that library conservators and technicians must employ in order to accomplish their work. In order to finish a single repair, I had to read up on and experiment with the mechanics of book structures, the composition and manufacturing process of leather, dyes, and metallurgy. Considering the myriad of materials and formats of information objects that are often housed within library collections, the training and expertise required to be an effective caretaker of those items is rather daunting. It is for these reasons, that professional development opportunities like the Lennox Foundation Internship for Preservation Education, Outreach, and Training are so important. In this current economic climate, when the available resources for academic and cultural institutions are particularly sparse, having the proper facilities, guidance, and room to experiment at one’s disposal is certainly a unique gift.
Great post. Thanks for the book reference, I need to find a copy. Most of my knives have lost all of the temper, and I’m usually right behind when I try to keep them sharp!
Love the pic of the magnets, and another great tip.