A Belgian Blue Waterstone works by releasing microscopic garnets, far harder than steel, that are carried in the ‘slurry’ that builds up on the stone surface in use. This slurry is actually made up of a mixture of hard, fine clay (the body constituent of the stone) and garnets.
This stone, because it is non-porous, cannot clog or become glazed. The obtuse facet edges of the round and oval garnets abrade the steel without the gouging that is common with more acutely angled abrasives. This leaves the steel with a much smoother polish and a noticeably finer edge.
This combination of speed and fine finish is unique. I find it a great hone to use and a very fine edge can be obtained by using progressively lighter pressure on the stroke. It has a distinctively different ‘feel’ and does cut rather more slowly than the yellow Coticule but gives an equally good finish. The slower cutting cuts the risk of over-honing. Specific slurry stones are available to help create a slurry and so speed up the process.