With the discovery of metalworking, mankind developed methods to sharpen and maintain knives by grinding. In the process, some particularly well-suited abrasives crystallized in all parts of the world. Some volcanic stones and special methods are still used today.
History of grinding
With the malleability of metals through heating, the art of blacksmithing emerged. A knife blade for war and kitchen use had to be made as sharp as possible. While in Europe flint, garnet and shale were recognized as ideal abrasives, wet grinding methods on rocks of volcanic origin developed in Japan and China.
Both methods, refined thousands of times, are still the definitive ways of sharpening knives today. This was joined by the invention of abrasive paper in the middle of the 19th century. With the production capability of abrasive synthetic products, aluminum oxides and silicon carbides also gained acceptance as artificially produced abrasives. Metal and ceramics are used in individual cases.
Knife types and blade shapes
At the beginning of grinding, almost exclusively straight blades had to be sharpened. In the course of time, more and more special grinds and types of knives have been developed. Thus, today’s knives can be divided into three main groups:
Apart from the razor, several blade shapes exist in all knives. In addition to smooth blades, which are straight or curved or rounded, serrated blades and sawing blades are common, as in meat, bone and bread kn ives.
The grinding can consist of a single bevel on one or both sides of the metal edge. Normally, a straight back side, the blade face, meets a bevel on one side, the chamfer. In the case of so-called double chamfers, the grinding angle is broken into two parts. The flat angle from the center of the blade experiences a steeper “tilt” toward the edge of the blade. With serrated and saw grinds, regular horizontal bevel interruptions or troughs are placed between the cutting tips of the blade.
How to sharpen a knife
The original sharpening techniques evolved from smooth blades. Grinding on a whetstone has proven to be the most effective method. If the blade has an interrupted course, the knives must be sharpened without a whetstone or specially prepared abrasive forms.
Depending on the individual shape of the blade course, whetstones or rod-shaped tools are used. For this purpose, there are delta-shaped whetstones and sharpening rods made of ceramic or metal. The so-called sharpening rod made of metal, which has a file-like surface structure, is a typical “hollow tool”. However, it has limited sharpening capability.
To achieve optimal sharpening in bar form, diamond files in different sizes and shapes are the best choice. When knives are given to professional sharpening shops for sharpening, special machines with diamond or stone grinding attachments are usually used. When considering who grinds knives, the sharpness limit of this method should be taken into account for suppliers who use grinding machines with rotating wheels only.
Physical and chemical concomitants
Experts and experienced grinders swear by water stones of Japanese or Chinese origin. Conditionally, artificially produced water sharpening stones are similarly efficient. A knife is a result of individual forging work, apart from machine “pressed” mass-produced goods. Each blade acquires a unique profile both during manufacture and in use.
Therefore, when manually sharpening a knife, professionals treat the blade almost as an individual. In addition, there are initial requirements of the unique blade such as the material or alloy and the shape and thoroughness used in tempering the knife. Both smooth blades and blades interrupted by hollows cannot develop their optimum sharpness when rigidly adhering to a uniform angle when sharpening according to instructions.
Sharpening potential and grinding burr
During “everyday” sharpening of a knife in a private household, usually only a reduced sharpening potential is achieved. The actual cutting ability depends decisively on the basic sharpening of the knife. Basic sharpening is recommended at least once a year for normally used household knives. A razor should be sharpened two to four times a year according to perceived sharpness.
Often not considered by laymen is the inevitable formation of a grinding burr. It not only impairs the degree of sharpness, but also transfers metallic “flour” to the cutting goods such as food. The burr should be removed after a sharpening operation, even during “everyday” sharpening, by appropriate finishing such as honing.
Maintain sharpness with storage and care
To make sharpening a knife worthwhile in the long run, the blade should be exposed to the least possible stress. Storing the knife unprotected in a drawer with other knives or kitchen tools will inevitably cause the blade to bump into metal and other materials. Any contact “hurts” the edge, and blunt impact literally “dulls” the sharpened steel edge.
Tips such as a protective coating over knife blades or a knife block will protect the grind. Magnetic retaining strips always require controlled attachment of the knife without blade contact. When cleaning and caring for the knife, always work in the direction of the blade.