The scanning electron microscope allows imaging of a honed blade’s edge (or apex) at sufficiently high magnification and contrast to assess the polish of the bevel, the uniformity of the edge and to make relative comparisons of sharpness.īelow, two SEM images taken edge-on of honed blades. Correlation of the microscopic edge characteristics to the shaving performance is also a topic to be investigated. This provides an added layer of complexity, identifying the properties of a blade that affect the selectivity of cutting whiskers over cutting skin. The intriguing aspect of a straight razor edge is the fact that it can be evaluated in a especially sensitive way, slicing hard whiskers from some of the softest and most sensitive skin. At the same time, the limit of what can be achieved with honing and stropping of a steel blade is on the order of 50nm. I will show that the apex of the blade must be thinned to about 100nm (one tenth of a micron) to comfortably shave facial whiskers. The expression razor sharp undoubtedly refers to the fact that the keenness required of a functional straight razor is very near the limits of what the physical properties of steel permits. In our experiments, the use of a straight razor will allow us to fix the honing angle at the value determined by the spine thickness and blade width. The steel used in a straight razor is hardened and tempered to optimize the achievable keenness. Honing on a flat surface with the bevel and spine contacting the hone fixes the angle of the apex. The centuries old design of a straight razor provides the ideal system for scientific study of sharpening. The goal is to provide an understanding of what is happening at the blade’s edge. My approach will be to use electron microscopy to physically observe the geometry and polish of the edge and to quantify the edge width and bevel angle. To a Scientist, this phenomenological approach begs the questions of why? and how? and provides little insight into how the process can be improved. Such comparisons are more than sufficient to allow a practitioner to develop and evaluate a honing procedure. Comparing the force to cut, the smoothness of the chiseled wood, the thinness of the sliced vegetable, or the closeness of the shave provides a relative quantification of sharp. The simplest and most common is through comparison and evaluation of use. In principle, there are two general approaches to quantifying “sharp” or the keenness of a blade’s edge.
Undoubtedly, the modern preference for mechanized and disposable sharpening is the choice of convenience rather than a confirmation of quality. Whether sharpening by hand with hones and abrasives can produce a finer edge than industrial scale, mechanized sharpening seems likely, but it is something we will investigate.
With the proliferation of disposable utility blades and cartridge razors, what was once a commonplace skill has become a lost art, practiced mostly by knife enthusiasts, hand tool woodworkers and men who shave with straight razors. For centuries, men have sharpened tools, knives, swords and razors.
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