There are many types of man-made water stones, which vary primarily in the durability of the abrasive particles and the strength of the bond between them. Tough abrasives cut quickly and lose aggressiveness slowly. Less durable abrasives may cut well initially, but the rate diminishes as the particles dull. Stones with strong bonds wear slowly, releasing fresh, sharp abrasive at a lower rate than those with weak bonds, which release abrasive at a higher rate but wear more rapidly. Formulating a stone is a balancing act, since the properties of the abrasive particles and the bonds holding them together combine to affect cutting speed and wear resistance. Selecting a stone depends on what you sharpen most often and how much you are willing to spend.
To help you understand the options, the following guide is based on our testing and observations.
Familiar standbys, King water stones were among the first introduced to the West. Except for the very coarsest 200x stone, they are aluminum oxide abrasive in a resin bond. In our testing, they were effective in O1 steel but noticeably slower in tougher alloys such as A2. The particles fracture and dull after a short period, performing like progressively finer grits, and allowing you to move from a medium grit straight to a finishing stone. They are economically priced, require only a quick soaking before use, and are a good choice for honing softer tool steels, or when cost is a concern.
Norton water stones also use aluminum oxide abrasive, but our testing indicates they likely have weaker bonds than King because they abrade and wear more quickly. Though comparable in speed to King stones when sharpening O1 steel, Norton stones are noticeably quicker in A2 and M2. The faster release of fresh abrasive means that they polish less than King stones, making it more important to work through a progression of grits. Effective for sharpening O1 and similar steels, or occasional use with tougher alloys such as A2 or M2, they have the benefit of being ready for use after only a short immersion.
Bester/Imanishi ceramic water stones provide a good balance of speed and wear-resistance. We found that they abrade O1 steel significantly faster than King and Norton stones, and perform even more impressively on tougher alloys such as A2, M2, and Japanese steels. The combination of a durable abrasive with a moderately strong bond enables them to retain their aggressiveness while wearing more slowly than stones with a weaker bond. Because it takes a long time for the particles to dull, each grit provides a consistent scratch pattern without polishing to a finer pattern, as stones with less durable abrasive or stronger bonds do. Bester stones require about 15 minutes of soaking, but fine Imanishi stones need just a spritz, a good choice if you regularly sharpen tough steel or if a minimum of maintenance is important.
Sigma Power Select II stones are all about speed. Regardless of the alloy, we found they cut more quickly than even Bester/Imanishi stones; the difference is most apparent in very hard material, such as high-speed and Japanese steels. The durable abrasive is released more readily than with stones with a stronger bond, ensuring a steady supply of sharp particles. These stones wear at a more rapid rate than those with a stronger bond, but this is offset since their cutting speed minimizes use. Like Bester/Imanishi stones, each grit provides a consistent finish without polishing to a finer scratch pattern. The 1000x and 3000x need a few minutes of soaking prior to use; the 10000x needs only a spritz. These are our most costly water stones, and are highly prized by those who want to minimize the time spent sharpening.
All of these stones are easily flattened on a lapping stone, using silicon carbide grit, or with a diamond plate.