Hirth & Krause, Dealers in…Leather and Findings. Shoe Store Supplies, etc. Grand Rapids, MI: 1890.( p. 46)
Kevin Driedger , who writes the interesting Library Preservation blog, posted a useful comment a couple of months ago, wondering if I was making an erroneous assumption about how a Turkish bone was used. I guessed it was used for marking. Lately while reading a old supply catalogue for the shoemakers I realized it that shoemakers have two distinct types of bones, termed scratch bones and slick bones. Now I’m convinced that the Turkish cobbler’s bone I wrote about is a scratch bone. Turkish shoemakers now make European style shoes, not Ottoman.
Judging from the catalog descriptions, it seems the scratch bones (similar to a scratch awl?) were used for marking, and slick bone was used for burnishing or smoothing. I wonder if the right angles on the left end were also used to scratch a line? This shape, seems to have served as the template for the most common shape that bookbinders use, with one flat and one rounded or pointed end.
Below is a slick bone that I purchased with some other shoemakers tools. It is thicker than most of the cow bone folders that are commercially available to now, and has a pleasing natural shape. The facets of the somewhat crude shape are highly burnished, suggesting it was used with a far amount of force or speed, the accumulation of glue residue and deep scratches give it a gorgeous patina from use.
Peachey Conservation 
Maybe more than just two types: the shoemaker’s kit of tools was traditionally called “St. Hugh’s bones,” after one of the patron saints of shoemakers. The story is that on the eve of his martyrdom St. Hugh had nothing to leave, so he left his bones for other shoemakers to make tools of. I once took a workshop on making miscellaneous small tools (folders, knives, paste scrapers, etc) where some of the very divers raw materials available for people to play with included several human ribs, but I think no-one used them (too thin-walled and too strongly curved, is what I thought).
True enough. I wonder how long it will take for bookbinders to develop a specialized vocabulary for the various types of bone folders we use – folding, slitting paper, forming headcaps, turning in, etc….