SHAPTON - Japanese made ceramic honing "stone" fused to a sheet of tempered glass which allows the grit to be displayed. These cut remarkably quickly and are less prone to cupping than Japanese waterstones.
A hard bond is particularly suitable for high-alloy tool steels. The coarse-grained alloy constituents (e.g. chromium and vanadium) in tool steels require a stone that wears slowly.
 
The premium range from Japanese company Shapton is the glass-stone series. The sharpening particles are highly pure and homogeneous. This is noticeable when changing to finer grits: The traces from the previous grit are quickly ground out. A special bond allows quick sharpening on a flat surface. The sharpening stone has a base of tempered glass and is thus 100 % warp-free. Conventional sharpening stones may warp microscopically by absorbing water, but Shapton stones solve this problem with their extremely flat base of tempered glass.
Another advantage of the glass base is that the grit rating on the underside is always visible even after much use. Before use, spray the stones with water. It is not recommended to keep them in water permanently. White aluminium oxide abrasive.