1. Diamond Stones. I’ve used two, many years ago, to sharpen steel knives & found that the diamond coating wore away. They did work well at first, but then I was sharpening on the backing material. This puzzled me, because diamond is harder than steel, but have only recently read that the diamond particles are torn off the backing material because they stick to the softer steel. Diamond stones are recommended for sharpening ceramic knives only. This info about diamond stones & steel knives I got from an Edge-Pro article.

On the other hand, the surfaces of knives that have been looked after may blacken a little, but this is a different type of iron oxide than ordinary reddish rust. This black oxidation is mainly triiron tetraoxide (Fe3O4). It coats the surface of the metal and prevents ordinary rust from getting in. It will not discolor food and poses no threat to hygiene.
The truth is that there is no one recommendation that we can make that will meet everyone’s needs. Every sharpener’s needs are different and every sharpening toolkit will be different. In order to help beginning sharpeners get started with good sharpening stones to build around, we need to understand their individual needs. So with that in mind, let’s look at the basic needs of a beginning sharpener.
In addition, there are three broad grades of Japanese Water Stones consisting of the Ara-to (rough stone), the Naka-to (middle/medium stone) and, the Shiage-to (finishing stone). However, it should be noted that the various grades of natural Japanese Water Stones vary widely in both density and grit size from stone to stone and thus, they do not translate well to American or European abrasive standards. Furthermore, because they are significantly softer than Novaculite, Japanese Water Stones must be flattened more often and do not last as long as a either Novaculite or Coticule stones. But, because they form a slurry of fine particles when used, they also do a superior job of both cutting and polishing.
When you apply a sharp knife to the surface of a tomato, cucumber, carrot or other food item it should - if you are holding it firmly and applying minimal pressure - sink into the particular item without effort. As such all you really need to work on is your technique and making sure you keep your fingers out of the way. With a dull knife however things aren’t quite so simple. When you apply a dull blade to, say, a tomato it’s not going to slice into the skin. Instead the skin will be able to push back meaning you’ll need to apply ever more pressure to get the knife to penetrate. Increasing the pressure on the knife increases the likelihood of the knife slipping off the offending food item to one side or another. And if it slips to the side where your hand is attempting to hold the vegetable steady you could be in store for a very nasty cut. Because even a dull knife will cause injury if there’s enough force behind it.
Visually, a very sharp knife has an edge that is too small to see with the eye; it may even be hard or impossible to focus in a microscope. The shape near the edge can be highlighted by rotating the knife and watching changes in reflection. Nicks and rolled edges can also be seen, as the rolled edge provides a reflective surface, while a properly straightened edge will be invisible when viewed head-on.

Ye olde tomato test - After you have sharpened using one of the above sharpeners grab a firm tomato and try to slice it. If the blade is properly sharpened it will slice through the skin with virtually no effort and without pushing the skin inward first. If the skin is able to fight back against the blade then your knives are not properly sharpened yet.

"Sharpening is like a hangover cure," says Laurie Timpson, founder of Savernake Knives in Wiltshire. "If there was a cure and you knew about it, I'd stay at your house, crash on your sofa and have whatever it was when I woke up. Everyone would have it and there'd be no discussion. Everybody says they've created a perfect sharpening technique, and they haven't." 

I've been using these stones for the past day, and they work great. Once you get the technique down that works for you, you can sharpen any knife to the point it can cut through news paper. Tip: make sure you count the amount of times you pass through the stone on one side and do that same amount on the other side. What I usually do is if I know the knife is very dull or chipped, I do 100 passes on each side using the 400 grit. I test the blade on thick paper and if it cuts through I test it on news paper. If it doesn't cut through the news paper I do another 50 passes on each side. Repeat this until the blade can cut through newspaper. After, on the 1000,3000, and then the 8000 grit stone I do 50 passes on each side. This should make the blade very smoothe cutting and polish it. I plan on getting a strop or piece of leather to further polish the blade. The only thing I don't like about this is that this package is that it does not come with a dressing stone so you can re flatten/level the stone after using them.

Every few months, you'll notice that your chef's knife has a harder time yielding perfectly thin slices and precise dices. You might even find your knifework is slipping—literally. And aside from being annoying to cut with, a dull knife can be seriously dangerous. To keep your fingers (and your dinner) in good shape, you'll want to learn how sharpen a kitchen knife by using a whetstone or a sharpener, and maintain that edge by honing it with a steel rod.
Finally, once you've refreshed the edge on your knife, you need to hone the edge to make it true. What happens when you grind a new edge onto your knife is that the extreme edge of the blade becomes microscopically thin. That is why it's sharp. But being so thin means that it is easily bent to one side or the other, causing the knife to seem dull. It isn't dull, it's what's called out of true.

The newly designed dual-sided combination whetstone from Fallkniven features a super fine white ceramic stone (0, 1 micron) with a grit of 1400 to 2000 and the dark grey ceramic stone is made of synthetic sapphires (1 micron) and has a grit of 800-1000. There is no need to add any oil or water, just lay the blade on the stone, raise the blade's spine and deburr your blade on the grey side until it has a razor-sharp edge and then use the smooth white side to get a nice polished edge.
However, because the Belgian Blue stone generally occurs in relatively wide columns with much thinner layers of Vielsalm Coticule on either side adjacent to the slate, the Belgian Blue stone is more plentiful that Coticule and thus, it’s somewhat less expensive. But, it’s also somewhat softer than Coticule and is not divided into different grades as Coticule is. Furthermore, because it is a softer stone than Coticule, it is sold without a substrate layer.
Ease of use – Most people in search of a mechanical sharpener want one because they don’t want to be bothered with trying to achieve a perfect edge themselves using a stick or sharpening stone. They want predictable, first class results every time. In that case it’s important that the electric powered device is easy to use, achieves results quickly and with little effort and is designed with user safety in mind. Keep in mind too that it’s easy to apply too much pressure when using a mechanical sharpener and when that happens you’re likely to see unsatisfactory results. In addition there are subtle differences between mechanical devices designed for Asian-style knives and those designed for Western-style knives. This has to do with the sharpening angle discussed above. Don’t get an Asian sharpener if you don’t need precise control over your cuts.
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