Sharpness refers to the ability of a blade, point, or cutting implement to cut through materials with minimal force, and can more specifically be defined as the capacity of a surface to initiate the cut. [1] Sharpness depends on factors such as the edge angle, edge width, and the fineness of the cutting edge, and is aided by material hardness. This quality is found in a variety of naturally occurring forms, including certain kinds of rock, in plant thorns and spines, and in animal teeth, claws, horns, and other structures serving various purposes. Sharpness is also a critical attribute for man-made tools ranging from kitchen knives and scissors to industrial cutting equipment, as it allows the user of a sharp implement to efficiently penetrate surfaces, or neatly divide other materials into smaller portions as needed.
A balance must be found between the sharpness and how well it can last. Methods that can circumvent this include differential hardening. This method yields an edge that can hold its sharpness as well as a body that is tough. [2] Different methods have been developed to sharpen surfaces, and to test surfaces for relative sharpness.
Some materials in the environment naturally break with extremely fine edges. A notable example is obsidian, a volcanic glass that fractures in a way that produces edges sharper than most metals can attain. Ancient civilizations utilized obsidian for crafting blades and tools due to its razor-sharp quality, which can be sharp enough to cut at the cellular level. Similarly, materials like flint and chert also fracture with sharp edges, making them useful as early cutting tools. Obsidian is still employed for its natural sharpness, with obsidian scalpels being experimented with in surgery for highly precise cuts. [3]
Sharpness is also a significant evolutionary trait in nature, providing various species with tools for survival. Predatory animals, such as big cats, sharks, and birds of prey, tend to evolve sharp teeth, claws, or beaks to efficiently capture and consume prey. These natural cutting implements are often optimized through narrow angles, and composed of hard materials like enamel. The sharpest teeth in nature are found in great white sharks, and viperfish, respectively, with the great white having serrated cutting teeth and viperfish having piercing needle-like teeth. Some prey animals such as deer and antelope, have similarly evolved sharp horns or antlers to deter attacks, while others, like porcupines and hedgehogs have spines or quills, which create a sharp, defensive barrier. Some herbivores have evolved sharp teeth or claws to access tough plants. For instance, beavers use sharp incisors to chew through wood.
Plants have also developed sharp structures, such as thorns, spines, and prickles, as defensive mechanisms to deter herbivores. These structures, found in species like cacti and roses, have pointed, sometimes serrated edges to maximize damage while requiring minimal energy to maintain.
Early humans made tools from both environmental materials such as sharp stones, [4] and biological materials such as plant spines and animal antlers, [5] for their sharpness. Obsidian scalpels older than 2100 BC have been found in a Bronze Age settlement in Turkey. [6]
Visually, a very sharp knife has an edge that is too small to see with the eye; it may even be hard or impossible to focus in a microscope. The shape near the edge can be highlighted by rotating the knife and watching changes in reflection. Nicks and rolled edges can also be seen, as the rolled edge provides a reflective surface, while a properly straightened edge will be invisible when viewed head-on. [7]
A very sharp tool can produce finer, more controlled cuts. This is particularly important in fields like surgery, culinary arts, and crafting, where precision can affect the quality of the outcome. The sharper the implement, the less pressure the user needs to exert to produce a cut, thus minimizing strain and reducing the risk of accidents. For this reason, sharper tools are often counterintuitively safer than dull ones. While an injury caused by a sharper tool is likely to be more severe, the chance of injury is reduced when the tool is sharp enough to avoid strain in its use. [8] The use of sharp tools also requires personal protective equipment to prevent accidental injuries to their handlers, such as cut-resistant gloves. [9]
Sharpness may be measured for various purposes. For example, with animal teeth, "tooth cusp sharpness is commonly measured by radius of curvature (RoC), where cusps with higher RoCs are duller and cusps with lower RoCs are sharper. During interactions between single cusps and food items, sharper cusps reduce the contact area between the tooth and the food item, leading to a reduction in energy and reaction force needed to induce a fracture in the food item". [10]
The sharpness of a forged blade can be quantified according to the Blade Sharpness Index (BSI), which categorizes blades based on the force required to make a cut through a standardized material. This index provides a comparative measure, helping users assess and compare blade sharpness with precision. A higher sharpness index generally indicates a finer cutting edge, which requires less force to penetrate or slice through a test medium. [1]
A knife is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced by the Oldowan tools. Originally made of wood, bone, and stone, over the centuries, in step with improvements in both metallurgy and manufacturing, knife blades have been made from copper, bronze, iron, steel, ceramic, and titanium. Most modern knives have either fixed or folding blades; blade patterns and styles vary by maker and country of origin.
Obsidian is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Produced from felsic lava, obsidian is rich in the lighter elements such as silicon, oxygen, aluminum, sodium, and potassium. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows. These flows have a high content of silica, giving them a high viscosity. The high viscosity inhibits diffusion of atoms through the lava, which inhibits the first step (nucleation) in the formation of mineral crystals. Together with rapid cooling, this results in a natural glass forming from the lava.
In woodworking and carpentry, hand saws, also known as "panel saws", are used to cut pieces of wood into different shapes. This is usually done in order to join the pieces together and carve a wooden object. They usually operate by having a series of sharp points of some substance that is harder than the wood being cut. The hand saw is a bit like a tenon saw, but with one flat, sharp edge.
A scalpel, lancet, or bistoury is a small and extremely sharp bladed instrument used for surgery, anatomical dissection, podiatry and various handicrafts. A lancet is a double-edged scalpel.
A blade is the sharp, cutting portion of a tool, weapon, or machine, specifically designed to puncture, chop, slice, or scrape surfaces or materials. Blades are typically made from materials that are harder than those they are intended to cut. This includes early examples made from flaked stones like flint or obsidian, evolving through the ages into metal forms like copper, bronze, and iron, and culminating in modern versions made from steel or ceramics. Serving as one of humanity's oldest tools, blades continue to have wide-ranging applications, including in combat, cooking, and various other everyday and specialized tasks.
Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force.
A Japanese kitchen knife is a type of kitchen knife used for food preparation. These knives come in many different varieties and are often made using traditional Japanese blacksmithing techniques. They can be made from stainless steel, or hagane, which is the same kind of steel used to make Japanese swords. Most knives are referred to as hōchō or the variation -bōchō in compound words but can have other names including -kiri. There are four general categories used to distinguish the Japanese knife designs: handle, blade grind, steel, and construction.
A file is a tool used to remove fine amounts of material from a workpiece. It is common in woodworking, metalworking, and other similar trade and hobby tasks. Most are hand tools, made of a case hardened steel bar of rectangular, square, triangular, or round cross-section, with one or more surfaces cut with sharp, generally parallel teeth. A narrow, pointed tang is common at one end, to which a handle may be fitted.
A blade's grind is its cross-sectional shape in a plane normal to the edge. Grind differs from blade profile, which is the blade's cross-sectional shape in the plane containing the blade's edge and the centre contour of the blade's back. The grind of a blade should not be confused with the bevel forming the sharpened edge; it more usually describes the overall cross-section of the blade, not inclusive of the beveled cutting edge which is typically of a different, less acute angle as the bevel ground onto the blade to give it a cross-sectional shape. For example, the famous Buck 110 hunting knife has a "hollow ground" blade, with concave blade faces, but the cutting edge itself is a simple, flat-ground bevel of lesser angle. It would be difficult, if not impossible, to put a "hollow grind" onto the actual cutting edge of the blade itself, which is a very narrow and small bevel.
A bandsaw is a power saw with a long, sharp blade consisting of a continuous band of toothed metal stretched between two or more wheels to cut material. They are used principally in woodworking, metalworking, and lumbering, but may cut a variety of materials. Advantages include uniform cutting action as a result of an evenly distributed tooth load, and the ability to cut irregular or curved shapes like a jigsaw. The minimum radius of a curve is determined by the width of the band and its kerf. Most bandsaws have two wheels rotating in the same plane, one of which is powered, although some may have three or four to distribute the load. The blade itself can come in a variety of sizes and tooth pitches, which enables the machine to be highly versatile and able to cut a wide variety of materials including wood, metal and plastic. Band saw is recommended for use in cutting metal as it produces much less toxic fumes and particulates when compared with angle grinder and reciprocating saw.
A kitchen knife is any knife that is intended to be used in food preparation. While much of this work can be accomplished with a few general-purpose knives – notably a large chef's knife, a tough cleaver, a small paring knife and some sort of serrated blade – there are also many specialized knives that are designed for specific tasks. Kitchen knives can be made from several different materials.
In cooking, a chef's knife, also known as a cook's knife, is a cutting tool used in food preparation. The chef's knife was originally designed primarily to slice and disjoint large cuts of beef. Today it is the primary general utility knife for most Western cooks.
A serrated blade has a toothlike rather than a plain edge, and is used on saws and on some knives and scissors. It is also known as a dentated, sawtooth, or toothed blade. Many such blades are scalloped, having edges cut with curved notches, common on wood saws and bread knives.
A glass knife is a knife with a blade made of glass, with a fracture line forming an extremely sharp cutting edge.
Sharpening stones, or whetstones, are used to sharpen the edges of steel tools such as knives through grinding and honing.
Sharpening is the process of creating or refining the edge joining two non-coplanar faces into a converging apex, thereby creating an edge of appropriate shape on a tool or implement designed for cutting. Sharpening is done by removing material on an implement with an abrasive substance harder than the material of the implement, followed sometimes by processes to polish/hone the sharp surface to increase smoothness.
Knife making is the process of manufacturing a knife by any one or a combination of processes: stock removal, forging to shape, welded lamination or investment cast. Typical metals used come from the carbon steel, tool, or stainless steel families. Primitive knives have been made from bronze, copper, brass, iron, obsidian, and flint.
Knife sharpening is the process of making a knife or similar tool sharp by grinding against a hard, rough surface, typically a stone, or a flexible surface with hard particles, such as sandpaper. Additionally, a leather razor strop, or strop, is often used to straighten and polish an edge.
This glossary of woodworking lists a number of specialized terms and concepts used in woodworking, carpentry, and related disciplines.
A boot and shoe clicker is the person who cuts the uppers for boots or shoes from a skin of leather or piece of man-made material. This includes all components of the upper, including linings, facings, stiffeners, reinforcements for eyelets and zip-protectors.
A sharp knife's edge will reflect no light because the two sides of the knife come to a razor fine edge. Conversely, a dull knife's edge will appear shiny because the two sides of the knife form a blunt rounded edge which reflects light.