Sharpening knives on a weekly basis is essential for efficiency and safety when cooking. We will focus on sharpening with whetstones. The primary application we'll talk about is for knives, but this can be used for straight razors, wood planers, mandoline blades, scissors, and so on.
Once proficient with using whetstones, maintenance will take at most a couple of minutes each week. All of the necessary materials can be obtained for under $100.
Three basic characteristics of whetstones
I think these three characteristics are important to know about when evaluating whetstones:
1. Grit rating.
2. Does it require immersion in water?
3. Load up potential.
Grit rating is a number that measures the coarseness or the fineness of the material used in making the stones.
Soaking stones are stones that require immersion in water and splashing stones are stones that are ready to use right after putting some water on the surface. Pros and cons of soakers: They seem softer and less susceptible to loading up. Have to plan ahead because of immersion time. Pros and cons of splashers: Harder and more susceptible to loading up. Significantly more expensive.
Load up potential refers to the stone's ability to become dirtied with scrap metal which has been taken off in the sharpening process. The more a stone is prone to loading up, the more it will slow down the sharpening process as it will take time to clean off the surface.
Preparing for sharpening.
First, find out about the knife that's being sharpened. Knives which can be sharpened should have a proper blade and not some thin stamped sheet metal. Knives with a bolster guard are not ideal for whetstones as they get in the way of sweeping on a stone and can chip the stone. Most importantly, find the angle that the bevel was cut at and see whether the knife is double-edged or single-edged (almost all Western knives are double-edged).
Second, find out about the whetstones that are being used. Does it require soaking? Will it break if it's soaked? If it's susceptible to loading up, are you equipped with the tools (e.g. rust remover or whetstone flattener) effectively remove it?
Lastly, patiently practice maintaining the appropriate angle and make sure to not apply too much force when sharpening. Gradually move from coarse stones to finer stones. Be careful not to apply any pressure on edge-leading sweeps, as the knife may dig into the stone and chip it.
The sharpening process.
There are two parts of the process on each stone:
1. The sharpening phase consists of working one part of the knife at a time using back and forth sweeps.
2. The honing phase begins after a burr has developed on both sides of the knife, sweep the knife from the tip to heel a few times on each side.
Here's a demonstration by a very proficient knife sharpener. Check out their channel for detailed tutorials on sharpening single and double sided knives.
Which whetstones do I need?
Very coarse whetstones (below 1k) are not generally needed for dull kitchen knives that have been in regular use. I think that a 1k grit and intermediate stones up to an 8k grit stone should be sufficient for most uses. Anything above 10k is generally for things like wood planers, straight razors, and sushi knives with a high HRC rating. In addition to that, higher grit stones are difficult to maintain and very expensive.
The rest is a matter of preference. I personally own four stones in the 800 grit to 6k grit range. Naniwa Choseras (800, 3k) and King KDS (1k/6k combination). I also use a rust eraser, whetstone holder, and a leather strop (I'll add info about this if I find that it's useful).
Testing sharpness.
Sharpness tests should be conducted in scenarios which are actually relevant for the user (e.g. not cutting hair or paper). The most useful test for me has been julienning carrots. A that knife cuts through carrots like this is more than sufficient for all my needs.