This is a 4 volume set of books written in the 1850's with a ton of info.
Well worth browsing.....
Turning And Mechanical Manipulation | Charles Holtzapffel
A very good section on honing razors and a section on natural stones.
Interestingly the Coticule was referred to as a German waterstone and regarded as the best of the readily available stones. The Charnley Forest was regarded as a stone to use just before the Coticule. The Thuringen stones
are also mentioned but referred to as a blue or gray slate. The Arkansas stones were briefly mentioned and referred to the white translucent as the best. The authors son revised/updated the books 45 years later and was much more positive about the Arkansas stones.
Have a good read!,:)