Bookbinding 101: Bone Folder
A bone folder is your friend. You can probably make books without one, but it's just so darn handy, we wouldn't want to. It performs essential functions that could be done with your hand or some other tool, but it works so well, has so many uses, and costs so little, it's a no-brainer to add it to your tool kit.
It creases pages when you fold them, smooths out leather or paper when adhering them to the cover, creases in leather corners (inside the cover), tools paper or leather when creating embossed designs, burnish edges, make a temporary mark in fabric or leather, or any number of similar uses where you need to flatten, crease, or smooth something out.
A bone folder is traditionally made from bone, but can be made from a variety of materials, including plastic, teflon, and wood. Randy J. Arnold makes beautiful bone folders from wood, including this one made of rosewood, and this one made of ebony. Note: these are some of the exceptions to the "costs so little" statement made above, but considering that it's handmade with such beautiful craftsmanship, as is the box it comes in, it's a bargain.
We have and love to use folders made with real bone. They don't cost much and have a great feel. Two of our favorites are a 5" taper shaped, and Hollander's 8" (17-20 cm).
Teflon folders are supposed to not mark delicate paper and leather when burnishing, but being a bit pricy, we find the bone to work just fine. Teflon supposedly does not leave marks on paper however, Teflon can mark some papers, so it's a good idea to test before you burnish.