Don't know. Not sure that I really care, as these stones definitely did the job that was asked of them, and did it with ease, even for a beginner whetstone user. I'll probably stick with them, at least until I get a lot more experience. Though, I do see a 10,000 or higher grit stone in my immediate future - more to play around with, than a feeling of genuine need.
Heres why I wasn't impressed at first. I only used it for a few minutes on each side, which resulted in nothing. I watched a video online with a master chef using his stone, and he sharpened his knife for 10 minutes on each stone before moving up to a finer grit. I took this hint, and used sharpened my knife on each side of this stone for 10 minutes, which led to perfection.
Now it's time to polish. This is when you'll swap over from the coarse grit to the finer grit (make sure this side is wet, too). I found the knife still had a bit of grime on it, so I gave it a wipe clean beforehand. The motion is exactly the same as with sharpening, but you can apply slightly less pressure, and limit to roughly 30 strokes on each side. 
It helps you get the knack for a consistently correct angle BUT the idea falls apart a bit when it comes to the curve and taper part of the knife and if your knife has an excessively narrow (slicer/boner) or wide (cleaver) width. It will also mark up the sides of your knife which may bother some who are obsessed with the cosmetic appearance of their $150+ Japanese knives--I could care less.
However, due to limited natural deposits and extensive quarrying over the centuries, true, high quality, Japanese water stones are now few and far between and are very expensive. Thus, various companies are now producing synthetic Japanese Water Stones which generally have a more consistent composition and grit size than natural stones as well as often begin somewhat harder and thus, lasting a bit longer; not to mention being cheaper to purchase.
We have been helping customers find the right sharpeners for more than a decade. Selecting a sharpener can be difficult if you're not sure what you need. Our staff is trained to listen to your needs and to help you find the right sharpener the first time. We understand that it may be your first time sharpening, so we're available to help you if you have questions. Even if you're already a sharpening professional, our staff is available to answer your tough questions. We use what we sell, so you can be assured that when you purchase from us, we're able to help you with your sharpener.
Made in the USA means a lot! It sharpens quickly, whether you need to remove a lot or just a "tune up" on the blade edges. Because it's manufactured flat, it is excellent for planer blades and chisels. The ability to sharpen dry or with only water creates less of a mess than other types of sharpening stones. The no-hassle guarantee is a definite plus, though I would be surprised if you ever needed it.

Selecting the right sharpening angle is the next step in sharpening. For more detailed instructions on selecting the right angle, try reading this article. Regardless of the method of sharpening, a appropriate angle should be selected. This angle doesn't need to be exact but following some general guidelines is a good idea. Most knife manufacturers recommend a roughly 20 degree angle. Depending on the use of your knife, you can move up or down from that angle. A fillet or slicing knife is never used on anything hard so an angle a few degrees less will produce a sharper edge. On the other hand, a survival knife with various uses can benefit from a more durable edge a few degrees larger.

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