I recently bought a set of diamond sharpening 'stones' to try them out:
http://www.screwfix.com/app/sfd/cat/pro.jsp?id=10468&ts=58127

I've used them a few times now, mainly to sharpen knives. The first
couple of times they seemed to work pretty well, giving a nice edge
quite quickly. But now it seems that much of the diamond has rubbed off
the steel backing. They don't sharpen so well.

I've been using them dry, and in much the same way one would use a dry
stone to sharpen a knife. Is it my fault, or do they wear down quickly?
Experiences?


--
Grunff