Honing slates are an interesting thing.
You can pay $1300 for an Escher or $1 for a piece of landscaping slate.
What are the differences? How good are slates you find in your yard or random unidentified slates from a century old toolbox?
Quite a few modern hone vendors have started hawking slate hones in the past few years. They seem to spring up near where slate was already being mined for construction and other purposes. How does this come about?
Well, basically. They understand something most honers don't seem to about slate.
Slate is, almost by its definition suitably fine-grained for honing. And frequently suitably consistent. Both of these do have some variance of course and that can be noticeable in honing... but pretty much any slate you pick up isn't going to be "too coarse" for a finishing hone.
What CAN make a slate a poor or challenging stone to finish on seems to be silica content (too low and the hone is either too slow or just plain ineffective as the silica is too obstructed to effectively hone). Is this a problem for a lot of slate? Yes. Solution? Use slurry. Is it a perfect solution? No, it adds additional management of the hone and doesn't change the fact that there's a bunch of useless material interfering with honing, it just makes that material mobile enough the silica can work around it to some extent. But it is a solution for a LOT of slate that would be far less effective as a hone without it, and can even turn some slates that are quite bad hones into passable ones. What it can't do is turn a bad slate into a good one or a good slate into a great one. Slurry with slates helps correct for the stones shortcomings and can often increase speed when necessary. It is useful in situations, but isn't a magic tool to increase a slates refinement outside of quite specific circumstances. Related to and compounding this problem can be other traits of the slates makeup. Overly friable and soft stones can crumble away at the microscopic level rather than providing a consistent plane for the razor to be ground against and overly hard slates can become worn in at the surface to such an extent that their abrasion can't keep up with the wear on the edge from the act of honing... leaving the honing process treading the water of a perpetually damaged edge the hone is incapable of fixing.
Thuringians may be the go to example of an exceptional slate, both for their general suitability as a hone, and imperceptible qualities specific to them making their edges especially suitable for shaving. Still, I've had hundreds of perfectly usable slates of all sorts pass through my hands, and frankly the majority were quite useful and very reasonable options for a razor finisher if nothing else were available. Ironically, they sell for almost nothing unless mistaken for a Thuringian, La Lune, or similar iconic hone. While it's unlikely any random vintage honing slate will match a Thuringian, in my experience they tend to quite handily best the avg you'll get from the slate being sold currently as honing slate, and about one in six to one in ten seems to get up into the realm of quality that sets it apart as a quite good finisher. My suspicion is that likely slate hones were made from just about any slate that was being mined in a given region, and the ones that survived lean towards survivors bias... meaning they're the ones that were good enough to be taken care of, while the lesser examples tended to be used until something better came along and were tossed. Modern slates being dug up for paving and repurposed as "razor hones" don't have this advantage... and let's not even get into the nightmare of "barber" hones... where you'll buy twenty for every halfway useful one you get.
You can pay $1300 for an Escher or $1 for a piece of landscaping slate.
What are the differences? How good are slates you find in your yard or random unidentified slates from a century old toolbox?
Quite a few modern hone vendors have started hawking slate hones in the past few years. They seem to spring up near where slate was already being mined for construction and other purposes. How does this come about?
Well, basically. They understand something most honers don't seem to about slate.
Slate is, almost by its definition suitably fine-grained for honing. And frequently suitably consistent. Both of these do have some variance of course and that can be noticeable in honing... but pretty much any slate you pick up isn't going to be "too coarse" for a finishing hone.
What CAN make a slate a poor or challenging stone to finish on seems to be silica content (too low and the hone is either too slow or just plain ineffective as the silica is too obstructed to effectively hone). Is this a problem for a lot of slate? Yes. Solution? Use slurry. Is it a perfect solution? No, it adds additional management of the hone and doesn't change the fact that there's a bunch of useless material interfering with honing, it just makes that material mobile enough the silica can work around it to some extent. But it is a solution for a LOT of slate that would be far less effective as a hone without it, and can even turn some slates that are quite bad hones into passable ones. What it can't do is turn a bad slate into a good one or a good slate into a great one. Slurry with slates helps correct for the stones shortcomings and can often increase speed when necessary. It is useful in situations, but isn't a magic tool to increase a slates refinement outside of quite specific circumstances. Related to and compounding this problem can be other traits of the slates makeup. Overly friable and soft stones can crumble away at the microscopic level rather than providing a consistent plane for the razor to be ground against and overly hard slates can become worn in at the surface to such an extent that their abrasion can't keep up with the wear on the edge from the act of honing... leaving the honing process treading the water of a perpetually damaged edge the hone is incapable of fixing.
Thuringians may be the go to example of an exceptional slate, both for their general suitability as a hone, and imperceptible qualities specific to them making their edges especially suitable for shaving. Still, I've had hundreds of perfectly usable slates of all sorts pass through my hands, and frankly the majority were quite useful and very reasonable options for a razor finisher if nothing else were available. Ironically, they sell for almost nothing unless mistaken for a Thuringian, La Lune, or similar iconic hone. While it's unlikely any random vintage honing slate will match a Thuringian, in my experience they tend to quite handily best the avg you'll get from the slate being sold currently as honing slate, and about one in six to one in ten seems to get up into the realm of quality that sets it apart as a quite good finisher. My suspicion is that likely slate hones were made from just about any slate that was being mined in a given region, and the ones that survived lean towards survivors bias... meaning they're the ones that were good enough to be taken care of, while the lesser examples tended to be used until something better came along and were tossed. Modern slates being dug up for paving and repurposed as "razor hones" don't have this advantage... and let's not even get into the nightmare of "barber" hones... where you'll buy twenty for every halfway useful one you get.