I found this on Neil's site on a description of a Lyn Idwal hone:
Lyn Idwal Welsh Hone Stone / Oilstone

"In the literature available this stone is likened to a Charnley Forest hone, but harder. It is mentioned as far back as 1798. It would have been as popular as the Charnley Forest hones at the time, but for its price - it was a more expensive stone than the Charnley Forest. This particular example is a bit softer than the other Llyn Idwal stone I have listed, and it does not give quite as refined an edge. To the naked eye the bevel it produces is quite polished, but upon magnification lots of slight scoring is apparent - just like you would see left behind by a CF stone. I have shaved off the stone and got a reasonable shave, but not in the same league as with the CF I use for comparisons. This is possibly due to the fact that it has only been lapped to 325 grit - no doubt 600 grit or higher would improve its edge (or honing a few more razors - I have honed two on it and the dull surface is now getting quite shiny: these stones are at their best when it is quite glass-like) and using a light honing oil would improve it a little more."