Japanese water stones first became popular and more available in the West in the 1970’s and 1980’s, but the selection was limited. They are, perhaps, the most popular general sharpening medium, valued for their quick cutting speed, consistency of finish, and broad range of grits.
What Should I Do First?
Water stones should be soaked before use and kept wet during use with frequent splashes of water. A spray bottle is handy.
Some stones require more soaking than others. Soft, porous stones can require prolonged soaking (about half an hour); hard stones require very little, if any, and may just need a spritz before use.
What Routine Maintenance Do I Need to Perform?
Lap your water stones every 3 to 5 minutes of use to maintain a flat surface. Allowing them to get seriously out of flat will have a frustratingly negative effect on sharpening. Lapping also removes any accumulated swarf. Below is an image of what not to do!
There are many methods for lapping water stones. Because the objective is to make the stone flat, the lap itself must also be flat. Here are suggestions for what you can use.
- Commercial lapping stones
- Coarse wet/dry paper on tempered glass or a thick stone tile
- Drywall screen on tempered glass
- Silicon carbide on tempered glass; the glass used should be at least 1/4" thick and, because the work surface may not be flat, supported by flat plywood, MDF or similar so it does not flex
- Diamond lapping plate; be sure it’s specially designed for flattening water stones, as some types of diamond stones for sharpening won’t stand up to lapping
The first method is to lap each stone on the lapping medium, rinsing the lapping medium after each use to prevent contamination by transferring particles from coarse to finer stones.
The second method is to lap first the coarse stone on the lapping medium, then progressively lap each stone on the previously lapped stone. So, the medium is lapped on the coarse and the fine is lapped on the medium. The idea here is that you remove the least amount of material from the finer stones.
In both cases, use a squiggle of soft pencil to mark the stone so you can see what you are doing. Lap until the pencil marks have been removed, but don’t worry if the lapping does not reach all the way into the corners as those areas of the stone are not as critical.
A related issue is to minimize uneven wear on the stone. Do this by using as much of the surface as possible. This minimizes the amount of material you must lap away to make the stone flat. In the image below, you can see that the chisel has been working into the corners of the stone rather than just abrading in the middle of the surface. The stone will be turned end for end shortly to distribute wear.
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