Japanese waterstones have a reputation for rapid sharpening. The loose bond between the individual grains means that as they become blunted they are washed out rapidly and give way to new, sharp grains.
Waterstones do require water to perform their magic! Never use oil, for it will ruin your stone. Never expose wet stones to temperatures below 0 ° C - they may break. Never leave Japanese waterstones permanently in water.
Before you use it, put the sharpening stone into water - five minutes will usually suffice, ten minutes are acceptable for coarse stones. Rest the stone on a non-slip base or wedge it between two pieces of wood. Use as much of the surface of the stone as possible, so that you postpone as long as possible the inevitable hollowing effect. Although the scum formed in grinding should be rinsed off regularly, it can be left on at the stage where you need a finer sharpening effect - as with a finer stone, which is useful towards the end of the sharpening process. Before changing to a finer stone, clean the tools to avoid carrying coarse grit into the next step of the sharpening process.
Select the stone according to the purpose. You can take as a guide the following:
1. For coarse work - grinding out notches or starting on a very blunt tool - a 120 - 400 grain stone is recommended.
2. For ordinary sharpening the right stone will have an 700 - 2000 grain size.
3. To hone away the fine burr and to polish the surfaces, use the 3000 - 12000 grain stones.
The stone must be plane. A stone that is worn and has become concave will never give a good result. In this case it must be flattened before you can use it. Japanese water stones are easy to get plane because they are soft, with a loose composition. They do, of course, require the process more often for this reason. There are various ways of doing this:
1. Rubbing two stones together is the oldest and commonest method.
2. Take a flattening stone which is specially manufactured for the purpose, dribble a little water onto its surface, add a teaspoonful of silicon carbide powder, and you can then work the stone round with circular movements under slight pressure.
3. A third possibility is to use wet-or-dry sandpaper, placing it wet on a plate of glass or other plane surface, where it will cling. If the stone is very hollow you can take as big a grain size as 80 or 120, and then a finer type to improve the surface. Here, too, you can add silicon carbide powder and you will double the speed of the word.
4.Wash the stone thoroughly after you have flattened it to avoid scratches on your tools.
Important advice for combination stones: Because the Japanese stones derive much of their effectiveness from the fact that the grit is only loosely bound together, it is only logical that the glue holding the stones together cannot be bombproof, and it is not at all uncommon for combination stones to separate. This is not a ground for complaint or return. One can simply take a water-resistant household glue, and rejoin the two halves, or just leave them separate, and use them as regular, single-grit stones.