A knife (plural knives) is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools.[1][2] Originally made of rock, flint, and obsidian, knives have evolved in construction as technology has, with blades being made from bronze, copper, iron, steel, ceramics, and titanium. Many cultures have their unique version of the knife. Due to its role as humankind's first tool, certain cultures have attached spiritual and religious significance to the knife. Most native Americans used them.[3]
Most modern-day knives follow either a fixed-blade or a folding construction style, with blade patterns and styles as varied as their makers and countries of origin.
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Today, knives come in many forms but can be generally categorized between two broad types: fixed blade knives and folding, or pocket knives.
Modern knives consist of a blade (1) and handle (2). The blade edge can be plain or serrated or a combination of both. The handle, used to grip and manipulate the blade safely, may include the tang, a portion of the blade that extends into the handle. Knives are made with partial tangs (extending part way into the handle, known as a "Stick Tang") or full tangs (extending the full length of the handle, often visible on top and bottom). The handle can include a bolster, which is a piece of material used to balance the knife, usually brass or other metal, at the front of the handle where it meets the blade. The blade consists of (3) the point - the end of the knife used for piercing; (4) the edge - the cutting surface of the knife extending from the point to the heel; (5), the grind, the cross section shape of the blade; (6) the spine - the thickest section of the blade; (7), the fuller, the groove added to lighten the blade; (8) the ricasso, the flat section of the blade located at the junction of the blade and the knife's bolster or guard; (9) the guard, the barrier between the blade and the handle which protects the hand from an opponent, and (10) the end of the handle, or butt. A choil, where the blade is unsharpened and possibly indented as it meets the handle, may be used to prevent scratches to the handle when sharpening or as a forward-finger grip. The knife's handle or butt may allow a lanyard (11) to be used to secure the knife to the wrist, or a portion of the tang to protrude as a striking surface for hitting or glass breaking.[4] Single edged knives may uitilze a reverse edge or false edge, in which the forward section of the knife's spine (opposing the sharpened edge) is thinned and left unsharpened.
Knife blades can be manufactured from a variety of materials, each of which has advantages and disadvantages. Carbon steel, an alloy of iron and carbon, can be very sharp, hold its edge well, and remain easy to sharpen, but is vulnerable to rust and stains. Stainless steel is an alloy of iron, chromium, possibly nickel, and molybdenum, with only a small amount of carbon. It is not able to take quite as sharp an edge as carbon steel, but is highly resistant to corrosion. High carbon stainless steel is stainless steel with a higher amount of carbon, intended to incorporate the better attributes of carbon steel and stainless steel. High carbon stainless steel blades do not discolor or stain, and maintain a sharp edge. Laminate blades use multiple metals to create a layered sandwich, combining the attributes of both. For example, a harder, more brittle steel may be sandwiched between an outer layer of softer, tougher, stainless steel to reduce vulnerability to corrosion. In this case, however, the part most affected by corrosion, the edge, is still vulnerable. Pattern-welding is similar to laminate construction. Layers of different steel types are welded together, but then the stock is manipulated to create patterns in the steel. Titanium is a metal that has a better strength-to-weight ratio, is more wear resistant, and more flexible than steel. Although less hard and unable to take as sharp an edge, carbides in the titanium alloy allow them to be heat-treated to a sufficient hardness. Ceramic blades are hard, brittle, and lightweight: they may maintain a sharp edge for years with no maintenance at all, but are as fragile as glass and will break if dropped on a hard surface. They are immune to common corrosion, and can only be sharpened on silicon carbide sandpaper and some grinding wheels. Plastic blades are not especially sharp and typically serrated. They are often disposable.[5]
Steel blades are commonly shaped by forging or stock removal. Forged blades are made by heating a single piece of steel, then shaping the metal while hot using a hammer or press. Stock removal blades are shaped by grinding and removing metal. With both methods, after shaping, the steel must be heat treated. This involves heating the steel above its critical point, then quenching the blade to harden it. After hardening, the blade is tempered to remove stresses and make the blade tougher. Mass manufactured kitchen cutlery uses both the forging and stock removal processes. Forging tends to be reserved for manufacturers' more expensive product lines, and can often be distinguished from stock removal product lines by the presence of an integral bolster, though integral bolsters can be crafted through either shaping method.
Knives are sharpened in various ways. Flat ground blades have a profile that tapers from the thick spine to the sharp edge in a straight or convex line. Seen in cross section, the blade would form a long, thin triangle, or where the taper does not extend to the back of the blade, a long thin rectangle with one peaked side. Hollow ground blades have concave, beveled edges. The resulting blade has a thinner edge, so it may have better cutting ability for shallow cuts, but it is lighter and less durable than flat ground blades and will tend to bind in deep cuts. Serrated blade knives have a wavy, scalloped or saw-like blade. Serrated blades are more well suited for tasks that require aggressive 'sawing' motions, whereas plain edge blades are better suited for tasks that require push-through cuts (e.g., shaving, chopping, slicing).
A fixed blade knife, sometimes called a sheath knife, does not fold or slide, and is typically stronger due to the tang, the extension of the blade into the handle, and lack of moving parts.
A folding knife connects the blade to the handle through a pivot, allowing the blade to fold into the handle. To prevent injury to the knife user through the blade accidentally closing on the user's hand, folding knives typically have a locking mechanism. Different locking mechanisms are favored by various individuals for reasons such as perceived strength (lock safety), legality, and ease of use. Popular locking mechanisms include:
Another prominent feature on many folding knives is the opening mechanism. Traditional pocket knives and Swiss Army Knives commonly employ the nail nick, while modern folding knives more often use a stud, hole, disk, or flipper located on the blade, all which have the benefit of allowing the user to open the knife with one hand. The wave feature is another prominent design, which uses a part of the blade that protrudes outward to catch on one's pocket as it is drawn, thus opening the blade; this was patented by Ernest Emerson and is not only used on many of the Emerson knives, but also on knives produced by Spyderco and Cold Steel as well.
Automatic or switchblade knives open using the stored energy from a spring that is released when the user presses a button or lever or other actuator built into the handle of the knife. Automatic knives are popular amongst law enforcement and military users for their ease of rapid deployment and their ability to be opened using only one hand. Automatic knives are severely restricted by law in most American states.[6]
Increasingly common are assisted opening knives which use springs to propel the blade once the user has moved it past a certain angle. These differ from automatic or switchblade knives in that the blade is not released by means of a button or catch on the handle; rather, the blade itself is the actuator. Most assisted openers use flippers as their opening mechanism. Assisted opening knives can be as fast or faster than automatic knives to deploy.
A sliding knife is a knife which can be opened by sliding the knife blade out the front of the handle. One method of opening is where the blade exits out the front of the handle point-first and then is locked into place (an example of this is the gravity knife). Another form is an O-T-F (out-the-front) switchblade, which only requires the push of a button or spring to cause the blade to slide out of the handle, and lock into place. To retract the blade back into the handle, a release lever or button, usually the same control as to open, is pressed. A very common form of sliding knife is the sliding utility knife (commonly known as a stanley knife or boxcutter).
The handles of knives can be made from a number of different materials, each of which has advantages and disadvantages. Handles are produced in a wide variety of shapes and styles. Handles are often textured to enhance grip.
More exotic materials usually only seen on art or ceremonial knives include: Stone, bone, mammoth tooth, mammoth ivory, oosik (walrus penis bone), walrus tusk, antler (often called stag in a knife context), sheep horn, buffalo horn, teeth, mop (mother of pearl or "pearl") etc. Many materials have been employed in knife handles.
As a weapon, the knife is universally adopted as an essential tool. It is the essential element of a knife fight. For example:
A primary aspect of the knife as a tool includes dining, used either in food preparation or as cutlery. Examples of this include:
As a utility tool the knife can take many forms, including:[5]
The knife plays a significant role in some cultures through ritual and superstition, as the knife was an essential tool for survival since early man.[2] Knife symbols can be found in various cultures to symbolize all stages of life; for example, a knife placed under the bed while giving birth is said to ease the pain, or, stuck into the headboard of a cradle, to protect the baby;[7][8] knives were included in some Anglo-Saxon burial rites, so the dead would not be defenseless in the next world.[9][10][11] The knife plays an important role in some initiation rites, and many cultures perform rituals with a variety of knives, including the ceremonial sacrifices of animals.[12] Samurai warriors, as part of bushido, could perform ritual suicide, or seppuku, with a tantō, a common Japanese knife.[13] An athame, a ceremonial black-handled knife, is used in Wicca and derived forms of neopagan witchcraft.[14][15]
In Greece a black-handled knife placed under the pillow is used to keep away nightmares.[16] As early as 1646 reference is made to a superstition of laying a knife across another piece of cutlery being a sign of witchcraft.[17] A common belief is that if a knife is given as a gift, the relationship of the giver and recipient will be severed. Something such as a small coin, dove or a valuable item is exchanged for the gift, rendering "payment."[8]
Knives are typically restricted by law, although restrictions vary greatly by country or state and type of knife. For example, some laws restrict carrying knives in public while other laws restrict private ownership of certain knives, such as switchblades.
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