Description
This is a Belgian coticule bout (“bout” = polygon), bonded to slate. One axis has been aligned to a ~6.5’Ø form, with a ~25’Ø shape affected across its the axis which is 90° to the ~6.5’Ø-shaped axis. Relative to the slate basis, this little guy did not form its curve “parallel” to the slate; that happens sometimes with natural stones, their density varies across the strata and just as a river develops a meander, some (natural only) stones will shape convex 1/parallel to their base.
You can work with a little stone like this with the razor and stone in hands, or with the razor stationary in a vise and rubbing the stone on the razor’s edge that way. The only function of this little stone is to carve in its 6.5’Ø effect to razors or other fine cutlery’s bevels, and you can either use it to create some concavity in the rear of the bevel and then leaving the front of the edge alone, or you can set the razor/knife entirely with this stone’s shape and then finish on a hanging strop or a flat/hard/fine finisher so that your actual apex is a more durable object. There would indeed be some straight razors that can hold a 6.5’Ø all the way through their bevel and shave just fine without any damage for many shaves, but that would be true of only the best kinds of razors, metallurgically speaking. It is more practical to use this in conjunction with another shape and abrasive mechanism.
For the primary shape of your bevel, face the stone’s length toward the spine-to-edge axis of the razor, and rub it along the length of the cutting edge while aligned in that fashion to the razor. Remember, there is a 25’Ø axis *across* the stone, so as you rub, when you’re nearer to the heel angle that border of the stone closer to the heel, and when you’re nearer to the toe angle the facet that’s closer to the toe a bit. This leaning effect will give sufficient grinding to the heel and toe without overcooking the middle. Don’t stop your work until you see the marks from this little stone overtaking at least 50% of your bevel’s width from spine to edge, and ~60-70% is likely a better target (but as I said, it varies by the knife at hand).
