Are there any coticules that are completely unusable for razor sharpening?
No. This is a myth, launched by people that don't know how to use them. It's easier to say that the fault is in the hone...
Coticules do take a different approach than synthetic water hones.Translating the methods for synthetic water hones to Coticules yields poor results.
During one of my visits at the quarry I have seen that sometimes (rarely) quartz inclusions can be present in the raw rocks. Should these inclusions be present in the hone, they would cause damage at the very edge. That's why the people at Ardennes Coticule cut the hones out of quartz free chucks, and if they do spot a small speckle of quartz in a hone they would never let that one to pass for sale.
Last update on 2009-08-29 by Bart Torfs.