Marvellous as the currently available diamond products are for so many purposes, I am a little wary of them for lapping sharpening stones. My reasoning, which could be mistaken, is that something only a little harder than the grit of the stone (or equally hard, in the casew of disposable paper) is more likely to expose fresh grains where diamond would blunten them but leave them in place. It isn't like razor sharpening will require you to flatten a deeply hollowed stone in a hurry.

I wonder if you can still find old televisions with a front of thick, very flat plate glass? Most I've seen lately are either flat-screen or have a bare, convex cathode ray tube.