I spent 10 years folding signatures by hand and finally made a bone folder from a deer antler
For about 10 years I folded every signature by running my thumbnail along the crease. It worked okay but my thumb would ache after a long day and the folds were never as sharp as I wanted. Then a guy at the Ohio Bookbinders Guild meeting in Columbus handed me a bone folder he made from a deer antler he found near his cabin. He said he just cut it, sanded it down, and polished it with beeswax. I tried it on a batch of 16-page signatures and the difference was instant. The crease came out crisp and flat with way less pressure, and my hands didn't hurt after 3 hours of work. I ended up making my own from a piece of antler I got at a flea market in Springfield for $4. Now I keep two on my bench, one for scoring and one for creasing, and I'll never go back to my thumbnail.