The title of this is a bit more general than it should be, but because I don’t think each of the separate hone slates is worth a full post. Lumping everything into one covers a lot of territory. As far as I know, the Water of Ayr is a slate, the purple hones that originated in Wales (often with little light green streaks or specks in them) are slate, and slate is found all over the world, so there are probably many many different regional slate hones and some slates that just aren’t very good at all.
Water of Ayr stones in a size useful for woodworking are probably enormously expensive now. I’ve got a couple of unlabeled small hones that are probably that, and one large hone that may be (not categorized here, because I’m not sure that it’s WoA). The suddenly valuable Eschers are hone slates (thanks to shaving forums, what was a $100 labeled collector’s stone quickly went to $600-$900 – the usefulness of those stones for razors vs. anything else is closer to the $100 range, but they are very uniform in characteristics, which makes them safe for a newbie- at least safe other than price).
For this post, I’ve chosen to show the work of two hone slates – a lower value unlabeled black slate that leaves a cloudy surface on steel, and a dandy little purple hone slate that I got from a very generous forum user and that I treasure for razors (even though razors rarely need to be sharpened).
Before showing the pictures, what’s the deal with the slates? They have limited cutting ability for their level of fineness, but can be very fine. It is *always* the case that a fine stone can be set up by a prior stone that’s much faster and slightly less fine, and in the world of japanese stones, the dippy fascination with a stone that’s “really fast and fine” is often bettered by getting two old used stones – a prefinisher, and a very fine and slow finisher. The latter combination may cost 1/6th as much and work twice as fast in combination, and also result in a finer edge. This is the case with hone slates, though they do vary somewhat in cutting power.
They do also like a slurry – stones that are a little slower quite often work well with a slurry and the same relationship holds with all stones – generally the slower a stone is when not slurried, the larger the disparity slurried vs. “clear water” on the surface. There are a few stones that are slow even on a slurry (chinese agate comes to mind, and reminds me that the agate may make a good base stones for loose diamonds, as it’s punchless on hard tool steel).
What am I moving toward? Like coticules, there’s no great reason to buy slates. There’s no reason at all to buy random slate stones that may look like a black arkansas stone.
Another forum user also gave me the coarse stone in the following two pictures. So, on to the pictures.
Compare these pictures to an 8000 grit Japanese Waterstone
First, a coarse black slate
Compare that to a fine vintage purple hone slate (suitable for razors)
Fine purple slate honed edge. Also slurried. At first glance, this doesn’t look that much finer than the picture above, but look again at the crispness of the edge and lack of rounding.
I have the benefit of using these stones and learning what visual cues result in use differences. I realize looking at the picture above leads you to see mostly the bevel itself and not the edge. But just as a tip here, compare the evenness of the edge and the shadowing that occurs at the top edge. It’s not really a shadow – the coarse slurry slightly rounds the edge but without leaving it that fine – that’s an artifact of the rounding. That is, the light from the microscope isn’t reflected back. A little bit of rounding might be nice, but only when the edge is fine.
When the edge on one of these pictures looks completely visually uniform and there’s no shadowing at all, you are moving toward something that would probably win a planing competition.
If you’re out hunting flea market stones and you see older stones that are black with tiny little sparkly specks and extremely smooth, those could be Water of Ayr and are worth picking up if they are only a few dollars (you can always offload them on ebay). If you see a small very smooth purple stone (vivid purple), especially if there are little mint green bits in it, same thing – just buy it. Anything else that’s slate without a label is probably not worth your time.
Of Making by Hand with Wood and Steel 