The Science of Knife Sharpening Explained


Do you know how to sharpen a knife blade correctly? Here are some invaluable science-led tips and secrets to keeping your kitchen knives on point.
The Science of Knife Sharpening Explained

Sharpening a knife blade is seemingly a simple task. When we try to do so ourselves, we obtain mediocre results, at best. In the worst-case scenario, we could irreparably damage the blade.

Today we are going to discover that sharpening is a scientific process that leaves little room for improvisation: here are some tips on how to sharpen a knife blade in the best way.


First, it is good to remember that a blade is sharp because its thin edge has numerous serrations at a microscopic level. With use, these notches are smoothed until they disappear, and sharpening is compromised: the blade then starts to become 'flat.' A little at a time, the serrations completely disappear and the blade is no longer able to cut the material. After all, a blade is a type of micro-saw. This is the time when it must be sharpened.


'Sharpening' means restoring the thin serration of the blade, as much as possible. It is not a simple task, as it is difficult for the naked eye to truly see how much a blade is sharpened. It is therefore worth putting some technical parameters into place in order to guarantee resistant and unparalleled sharpening.

There are essentially two types of sharpening: 'maintenance,' which can be done with another knife or sharpener, and true sharpening or 'grinding,' which is necessary when the blade cuts badly. In this case, a whetstone or sharpener is generally used.

A whetstone is a tool, usually of a ceramic or diamond-plated material, which sharpens the blade by means of rubbing. Even the classic 'wheel' of the knife grinder falls into this category, with the difference that it must be lubricated with oil or water compared to the manual version. It is good practice to also lubricate a manual whetstone with a little bit of sharpening oil. At this point, the blade should be slid on the whetstone in the opposite direction of its cutting edge. The work begins on the coarser side, which is used for grinding and then to the finer side, which is used for sharpening.


Speed is not as important as the consistency of movement, and, above all, the angle. Thousands of pages in physics books discuss the matter, and legends were born. We try to simplify our life: the smaller the sharpening angle between the whetstone and the blade, the sharper the blade becomes.

So is it necessary to sharpen at a very small angle? No, because sharpening also corresponds with greater fragility. As such, the sharper the blade is, the more often it has to be sharpened. This is why, with experience, it is necessary to find an angle that offers just the right compromise. A tip? According to many, the angle for perfect sharpening is 20°.


The sharpener is another tool, which is generally used for maintenance sharpening. It offers a lighter action compared to the whetstone, which is called 'realignment': in practice, its function is to put the microscopic indentation of the blade back in line after having been bent in different directions with intensive use.

Using the sharpener is simple: hold it firmly and slide it along the length of the blade with a linear and continuous movement. In this case, as well as the angle of the blade with respect to the tool must be approximately 20°.

Maintenance sharpening can be performed often, as soon as the blade starts to lose its 'cut.' When the sharpener is no longer enough, move on to the whetstone.

A final trick: use a coffee cup. In an emergency and if you find yourself without tools, take a ceramic coffee cup, turn it upside down and pass the blade a dozen times on the edge of the bottom of the cup, always at a 20° angle.