Every time you use your knife the edge gets worn down. Exactly how and to what extent it is affected depends on what you cut and how you work with the knife. But basically, what happens is that the cutting edge bends one way or the other. When you sharpen a knife, you are aiming to re-align the cutting edge again so that it becomes straight and thereby as sharp as possible.
Whetstones and sharpening steels are excellent tools for re-sharpening knives. They come in many different models, materials and thicknesses. Today, most people who use sharpening rods agree that polished steel is the best method for maintaining the sharpness of a knife. The exception to this is in the fishing industry where tradition inherited from the boats means that grinding equipment was seldom available, so the rough serrated steels have to a larger extent remained.
When mastering the art of sharpening, the first step is to understand the effect of the sharpening rod on the blade. For quality sharpening, with a polished steel rod or one with a fine abrasive surface, the task of the rod is to push back the bits of the edge that have moved to the side during contact with harder materials. Imagine how the edge of a knife looks under strong magnification, it has a smooth, even, sharp edge… and then imagine how careless treatment of the blade, for example against rough steel, can result in fraying and loose particles of steel (known as burr ). However, if you use a polished sharpening steel the edge can be smoothed out and the result will be a smooth and sharp edge once more.
The most important thing when you use a sharpening rod is the angle of the knife against the steel. You need to place the knife against the steel at the same angle that the very outer cutting edge has been ground to, and simultaneously pull the knife all the way at the same angle, from the hilt to the tip of the blade. If the edge is very damaged, the pressure against the steel can be relatively hard to be able to push the edge back, then gradually decrease to a feather-light stroke towards the final stages. The key here is to keep control of the movement and not be careless about any strokes, which usually doesn’t have any effect on the edge. How you hold the sharpening rod is not the most important thing from the point of view of the sharpening, as long as you have control and don’t exaggerate the sharpening angle – that results in a rounded cutting edge. However, the knife-edge should be pulled against the sharpening steel in somewhat of a cutting motion. Alternate between both sides of the edge, and then test if the knife is sharp.
Use both your eyes and ears while sharpening your knife – your eyes to make sure that you are holding the knife at the correct angle, and your ears to hear when the sound from the sharpening reduces as the edge becomes even and sharp.
Remember that knife sharpening is absolutely not a speed test. Using calm and controlled movements is the foundation for learning to sharpen a knife. And there’s no magnetic effect on the edge or any other mystical force that impacts the result either. The purpose of the magnetism in the sharpener is to collect loose particles at the top so that these don’t damage the edge during sharpening.
With practice and reflection you’ll soon learn how to sharpen a knife so that it becomes finely sharp again.