Maintaining the blade of any kitchen knife is not only great for cutting efficiency and quality, but is also a must for maintaining safety. Dull knives are the most common causes of knife injuries. Blunt knives require more force to use, which increases the likelihood of injuries. Additionally, cuts from a sharp knife heal more quickly than those from a blunt knife.
Knife sharpening is a process by which a knife is made sharp by grinding the blade against a rough, hard surface like a stone, or a soft surface with rough particles like sandpaper. The smaller the angle between the blade and the stone, the sharper the blade will become. This angle between knife edge and sharpening stone is called the edge angle, which equals the angle at which the blade is held. The edge angle for very sharp knives can be as little as 10 degrees, while knives that require a tougher edge such as a chopping knife should be sharpened at 25 degrees or more.
The composition of a sharpening stone will affect the sharpness of the blade. For example, a finer grain produces a sharper blade. The metal composition of the blade also affects the sharpness and some blades take and keep an edge better than others. There are various types of knife sharpeners including sharpening or oil stones or honing steel. The sharpening stone consists of a carborundum stone, a block of ceramic, or a metal plate embedded with diamond dust. There are also generally three grades of stones: coarse for renewing damaged blades, medium for general work, or fine stones to but a final edge back on the blade. Often these stones require a lubricant like oil to carry away the metal cuttings from the edge while sharpening and preventing the pores in the stone from becoming clogged with metal and grit during the sharpening process.
Honing steels are generally the choice of professional chefs. A steel generally consists of a hardened steel rod with tiny grooves scored lengthwise down the rod. These are very effective for sharpening and honing the edge of knife blades but they do tend to wear away the knife more quickly than a sharpening stone.