I've used ceramic rods, diamond plates, and leather strops for our sharpening needs. And, like most, I've tried a dozen little gimmicky sharpeners that, while some work, those that do often remove way too much material from the edge, making your blade wear down faster. I've also used oil stones, grinders and buffers for less meticulous sharpening of axes and such. These two stones from Unimi (600/1000 and 2000/6000) served as my introduction to whetstone sharpening. And I must say I like it. Though, I'm not sure of the need for investing in more expensive stones.

An important but often confusing area of sharpening is knowing when you're done with one stone and ready for the next finer grit. On coarse stones it is very easy. When you sharpen one side you will notice a burr forming on the opposite side of the edge. This burr is hard to see but is easy to feel. Very carefully feel for the burr by gently running your hand from the spine to the edge. (Do not run your finger along the knife edge from heel to tip, that's only asking for trouble!) A burr is formed when your stone removes material directly at the edge. The burr will move from one side of your knife to another as you alternate sharpening sides. Make sure you have felt the burr jump between both sides before you move on to the next finer stone. That will ensure that you have sharpened both sides effectively. The finer grits are done the same way but the burr is much smaller. On the finest grits you may not be able to notice the burr at all. Testing the knife sharpness will tell you when you're done. (Learn how you can test to see if your knife is sharp.)
Last, it should be noted that dual-sided Coticule/Belgian Blue whetstones are also sometimes available which have a layer of Belgian Blue stone on one side and a layer of Coticule on the other. Thus, these whetstones provide a softer, more coarse, grit on one side and a harder, finer, grit on the other. Plus, due to the inherent toughness of the Belgian Blue stone, these dual-sided stones do not require a substrate layer.
There will be a drawer that extends into the mechanism under the abrasives. Any detritus from the sharpening process drops into this drawer. Exactly where the drawer is located will differ from sharpener to sharpener but it shouldn’t be hard to find. Remove the drawer flick any material into the wastebasket and then wipe out the drawer with a damp cloth or tissue. You may want to use work gloves and goggles to protect your hands and eyes from any loose metal shavings. Once the drawer is clean and dry replace it. The exact means by which the sharpening mechanism itself is cleaned will vary from manufacturer to manufacturer. Consult your owners guide for specific details. Make sure you don’t introduce any grease or other lubricants into the sharpener unless specifically directed to do so by the owner’s manual. Also, the outside of the sharpener should come perfectly clean with just a damp cloth. Avoid using commercial cleaners or abrasives of any kind.
Your immediate goal is to raise a burr on the side of knife opposite to the side you are sharpening and depending on the steel, the grit of stone and how you are doing, it will be either a very quick process or it will seem like it takes an eternity. Patience here will reward you, believe me. The sharpening process is incomplete with no burr creation on your first stone. (Yes, it is possible to stop at that magic moment without the burr forming but we are not there yet, we don’t even need to go there, ever, I am just mentioning it so those gifted sharpeners will be happy) . Think of the burr as the debris that is making the knife dull being forced down the blade towards the edge and over to the other side of the by your sharpening prowess. You form the burr, that knife will get sharp, no burr, you just need to look at your work. A Loupe is handy here, an inexpensive magnifying device with a light that allows you to see the edge very well, if you are not forming a burr, you are not reaching the edge. (Having a loupe also makes you look cool and scientific, like a Sharpologist).
Also natural stones have a random grit size that gives a long lasting edge. Basically the random grits create varying sizes of micro-serration in the blade that wear down at a different rate, therefore longer edge retention. Whether this is true or not we really like natural stone, especially for sharpening tradition single bevel Japanese knives. Use natural stones with water – it’s far cheaper than sake.

Once sufficiently wet, it's time to position the stone on something solid, so it doesn't move about during sharpening. Many come with holders, but you can just place it on a slightly damp tea towel on the table. The stone should be roughly perpendicular to your body, though Warner told me it is sometimes easier to angle it ever so slightly to the right (if you're right handed). 
A: That depends almost entirely on how often you use them. If you are a professional chef who uses his or her knives every day then you should hone them every time you use your knives. But honing has its limits and over time your edge is going to become dull no matter what. Therefore your knives will need to be sharpened at least several times a year. Some chefs, in fact, will use a whetstone on an almost daily basis in order to ensure their knives are always razor sharp. Most of us, however, are not professional chefs and may not even touch our kitchen knives for days at a time. In that case, it’s probably a good idea to hone the edge after every couple of uses and have your knives sharpened once a year.
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