Knife

 
Traditional Finnish puukko knife
Traditional Finnish puukko knife

A knife is a sharp-edged hand tool used for cutting. A knife consists of a blade, usually sharpened to a point with one or more edges, attached to a handle. Knives have been used as tools and weapons since the Stone Age, in the dawn of humanity. Specialists recognize the knife as one of the first tools designed by human beings in order to survive.

The first knives were flint or other rock, chipped or ground to an edge, sometimes with a handle. Later on with advances in smelting and metallurgy the blades were made of bronze, iron, then steel. While the materials have changed over time, the basic design remains the same.

Together with the fork and spoon, the knife has been a common eating utensil in the Western world since at least the Middle Ages. Today, these are not frequently sharpened, and most sharp knives are used in kitchens. In the West, multi-purpose pocket knives are commonly carried, to be available anywhere. The importance of the knife as a weapon has declined as more specialized weapons have been developed, but the knife remains the universal tool.

Anatomy of a knife

A knife consists of a tang, a bolster, a blade and a handle. The tang is an extension of the blade into the handle. The bolster functions as a balance point and handguard, to prevent fingers from slipping onto the blade. The blade in turn consists of a tip, a spine, an edge and a heel.

A fuller, sometimes called a blood gutter or blood groove, is a groove on the side, along a blade. According to a popular myth, it lets bleeding occur from an artery without removing the knife. In reality, its only function is to make knives and swords lighter while sacrificing little strength; on most knives it has more decorative worth. Additionally, a groove on the blade can reduce surface tension between the blade and the item being cut, thereby allowing easier movement or removal of the blade.[1] Some knives also have a shoulder in which the blade thickens as it meets the handle. In piercing, this helps keep the knife from jamming, for example in bone. In kitchen knives, it keeps chopped items from moving back toward the hand.

The handle of a knife should be made of a non-slip material. For a large knife, it is desirable that the handle is thick enough that one's fingers just meet one's palm when the knife is gripped tightly. A hole in the end of the handles allows the knife to be hung or placed on a lanyard.

Blades

Forschner/Victorinox make inexpensive kitchen knives; high-end manufacturers include Wüsthof, Global, Henckels, Kershaw Knives and Böker (Tree Brand).

Materials

Knife blades are typically made of steel. All knife steel is tempered martensite, which means that a fine-grained crystal structure with lattice irregularities that make it hard. It is formed as it is quenched, changing it from the austenitic structure that it has at high temperature to a hard, but brittle martensitic structure. The blade is then tempered by heating to an intermediate temperature for a period to make it less brittle. Knife steel has fairly low nickel content, because nickel tends to keep steel in the austenitic structure, even when cold. Steels having high carbon but low chromium content ("carbon steel") are prone to rust and pitting if not kept dry and oiled.

Stainless steel knives have gained popularity in the latter half of the twentieth century. Stainless steel is steel with very high (12–18%) chromium content — stainless knife steels are high in carbon, but "carbon steel" means there is not also a lot of chromium. Stainless steel is highly resistant to corrosion (though knife steel is less so than higher nickel stainless steel) because, except in acid, one of the metals or one of the oxides is always stable Stainless steel knives usually only rust under extreme conditions. Stainless steel usually has particles of chromium (or other alloy metal) carbides. These explain its reputation for long wear (the carbides are harder than the metal) and for being harder to sharpen and not taking as good an edge as rustable, low alloy ("carbon") steel (the ceramic particles themselves cannot be sharpened easily.), although tests indicate that stainless steel knives hold an edge better than regular steels.[2] The bulk hardness and toughness of stainless steel tend to be lower than those of low alloy steel. Stainless and semi-stainless steels include D2, S30V, 154CM, ATS-34, and 440C.

A variety of exotic steels can be used to form blades; other materials may be used, although these are far less common than steel blades. Knife manufacturers such as Spyderco and Benchmade typically use 154CM, VG-10, S30V, and CPM440V (also known as S60V), as well as high-speed high-hardness tool steels like D2 and M2. Other manufacturers sometimes use titanium, cobalt, and cobalt containing alloys. All three are more ductile than typical stainless steels, but have quite a vocal support group despite concerns about health effects of cobalt content. The original craft of Damascus steel may be lost, but not being a registered trademark, the name is today used to apply to the equally old but less exotic pattern welding, which creates layered and admired patterns. The cost of the process restricts it to high-end knives. There is typically more demand for exotic alloys in the utility, outdoor, and tactical or combat knife categories than there is in the kitchen knife category.

Vanadium and molybdenum are important alloy metals because they make the grain size smaller, which improves hardness and toughness. Vanadium, and perhaps molybdenum, also increase corrosion resistance, although work by CATRA ( the World's cutlery technology centre) has found no corrosion benefits from vanadium.

Some manufacturers, particularly of kitchen knives, make ceramic blades; these are harder and stay sharp longer, but because of their brittleness, chip and break more readily.

Shapes

There are a variety of knife blade shapes; some of the most common are listed below.

Blade types

(1) A normal blade has a curving edge, and flat back. A dull back lets the wielder use fingers to concentrate force; it also makes the knife heavier and stronger for its size. The curve concentrates force on a small point, making cutting easier. Therefore, the knife can chop as well as pick and slice.

Clip Point blade
Clip Point blade

(2) A curved, trailing-point knife has a back edge that curves upward. This lets a lightweight knife have a larger curve on its edge. Such a knife is better for slicing than a normal knife.

Drop-Point blade
Drop-Point blade

(3) A double edged or spey blade has two edges. The idea is to make a blade that cuts in either direction, with a strong sharp point. This shape is primarily used for fighting knives (daggers, bayonets) because it can cut in both directions and point in line with the handle.

(4) A clip point blade is like a normal blade with the tip "clipped" to make the tip thinner and sharper. The back edge of the clip can have a false edge that can be sharpened to make a second edge. The sharp tip makes the blade exceptional as a pick, or for cutting in tight places. If the false edge is sharpened it increases the knife's effectiveness in piercing. The Bowie knife has a clipped blade.

A drop-point blade is very similar to a clip point, but it features the back convexed down, rather than having a clip taken out of it. It handles much like the clip-point.

(5) A sheepsfoot knife has a straight edge, and a curved dull back. It gives the most control, because the dull back edge is made to be held by fingers. Sheepsfoot knives are good for whittling, including sheep's hooves.

(6) An Americanized tanto style knife is thick towards the point. It is only superficially similar to the points on most Japanese long and short swords (katana and wakizashi). The traditional Japanese tanto knife uses the blade geometry of (1). The edge is straight. The point is actually a second edge on the end of the blade, with a total edge angle of 60-80 degrees.

An ulu (Inuit woman's knife) knife is a sharpened half-circle. This blade type has no point, and has a handle in the middle. It is good for scraping, and sometimes chopping. It is the strongest knife shape. An example is a head knife, used in leatherworking both to scrape down leather (reducing thickness), and to make precise, rolling cuts to form shapes.

Types of knives

Knives can be categorized based on either form or function.

Form

A fixed blade is a knife in which the blade does not fold and extends most of the way into the handle. This type of knife is typically stronger and larger than a folding knife. Activities that require a strong blade, such as hunting or fighting, typically rely on a fixed blade. Some famous fixed blade designs include the Ka-bar and Bowie knives.

A folding knife is one that has a pivot between handle and blade, allowing the blade to fold into the handle. Most folding knives are small working blades, and pocket knives are usually folding knives.

Some folding knives have a locking mechanism: The most traditional and commonplace lock is the slip-joint. This is not really a lock at all, and is found most commonly on traditional pocket knives. It consists of a backspring that wedges itself into a notch on the tang on the back of the blade. The lockback is the simplest true locking knife. It is found on most traditional locking knives. It is like a slip-joint, but the lock consists of a latch rather than a backspring. To disengage, one presses the latch on the spine of the knife down, releasing the tang. The linerlock is the most common today on knives, especially so-called "tactical" folders. Its main advantage is that it allows one to disengage the lock with one hand. It consists of a liner bent so that when the blade opens, the liner presses against the rear of the tang, preventing it from swinging back. To disengage, you press the liner to the side of the knife from where it is attached to the inside of the scales. The framelock is a variant of the linerlock, however, instead of using the liner, the frame functions as an actual spring. It is usually much more secure than a liner lock.

There are many other modern locks with various degrees of effectiveness. Most of these are particular to single brands, most notably Benchmade's AXIS™ lock and SpyderCo's Compression™ lock.

Many folding knives (particularly locking models) have a small knob or thumb-screw that allows the user to open the knife quickly with one hand.

Delta pocket knife
Delta pocket knife

In the Middle Ages, a dorsal meant a knife with a 'back', or a one-sided knife. An ansall was a two-sided knife, with a blade on both sides. These terms have since fallen out of use.

Function

In general, knives are either working knives (everyday-use blades), or fighting knives. Some knives, such as the Scottish dirk and Japanese Tantō function in both roles. Many knives are specific to a particular activity or occupation:

Indoor use

  • The main indoor use of knives is as piece of cutlery or as kitchen knife in various forms, including:
Old carving knife and carving forks, non-stainless steel.  Stag handles.  Note folding guards.
Old carving knife and carving forks, non-stainless steel. Stag handles. Note folding guards.
  • A bread knife is a special knife with a longer, serrated blade especially designed for easily cutting all types of bread. The blade is straight with a blunt end. The serrations (teeth) allow it to cut bread using less vertical force, so keeping the bread from being compressed. They also leave fewer crumbs than most other knives.
  • A boning knife is used for deboning meat, poultry, and fish.
For other kinds of kitchen knives, see the main article: kitchen knife.
  • A carving knife is for carving large pieces of meat such as large birds and roasts at the dining room table. Its appearance is, therefore, more emphasized than that of a kitchen knife.
  • A table knife is part of a table setting, along with spoons and forks. It can be a butter knife, more literally a small spatula, not intended to cut at all, or a steak knife, or it may serve both functions.
Old Swiss table knives with weighted ivory handles, non-stainless blades and forged guards. 24 centimetre (9½ in over-all length
Old Swiss table knives with weighted ivory handles, non-stainless blades and forged guards. 24 centimetre (9½ in over-all length
Old English table knife without original handle, non-stainless blade and forged guard. 15 centimetre length excluding handle
Old English table knife without original handle, non-stainless blade and forged guard. 15 centimetre length excluding handle
  • A palette knife is used by artists for tasks such as mixing and applying paint, and in cooking for spreading icing (in the U.S. this knife is referred to as a frosting spatula). Some palette knives have a serrated edge on one side.
  • For whittling (artistic wood carving) a blade as short as 25mm (1 inch) is common.
  • An electrician's knife is specially insulated to decrease the shock hazard.
  • A scalpel is a medical knife, used to perform surgery. It is one of the sharpest knives available.
  • Custom-made knives called microtomes are used to cut specimens for microscopy. The sharpest knives ever constructed are probably the ultramicrotomes with diamond edges used to slice samples for electron microscopes.

Outdoor use

Modern hunting knife (Rigid Custom Series) and sheath
Modern hunting knife (Rigid Custom Series) and sheath
1930s Remington hunting knife.  (The tip was broken and re-shaped.)
1930s Remington hunting knife. (The tip was broken and re-shaped.)
  • A hunting knife is normally used to dress large game. It is often a normal, mild curve or a curved and clipped blade. Note some hunting knives utilize a "gut hook" blade. This is a section on the top point of the knife which is specifically designed to cut skin in one clean motion (ie in gutting an animal).
  • A stockman's knife is a very versatile folding knife with three blades: a clip, a spey and a normal. It is one of the most popular folding knives ever made.
  • A dive knife or diver's knife is adapted for underwater use. Dacor dive knives have tough thermal plastic handles, durable sheaths, and a convenient push-button release, for example.
Machete blade
Machete blade
  • Utility, or multi-tool knives may contain several blades, as well as other tools such as pliers. Examples include Leatherman, SOG, Gerber, Wenger and Victorinox (The "Swiss Army knife") tools.
  • A kukri is a Nepalese fighting and utility knife with a deep forward curve.
  • A machete is a long wide blade, used to chop through brush. This tool (larger than most knives, smaller than a sword) depends more on weight than a razor edge for its cutting power.
  • A parang, bolo or golok is a knife very similar to a machete but heavier and with a blade designed to move the center of gravity further from the hand for increased chopping power in woodier vegetation.
Mexican Machete, from Acapulco, 1970.  Horn handle, hand forged blade taper (hammer marks visible.).  (Has been sharpened by owner.)
Mexican Machete, from Acapulco, 1970. Horn handle, hand forged blade taper (hammer marks visible.). (Has been sharpened by owner.)
  • A survival knife is a sturdy knife, sometimes with a hollow handle filled with equipment. In the best hollow-handled knives, both blade and handle are cut from a single piece of steel. The end usually has an O-ring seal to keep water out of the handle. Often a small compass is set in the inside, protected part of the pommel/cap. The pommel may be adapted to pounding or chipping. Recommended equipment for the handle: a compass (usually in the pommel). Monofilament line (for snares, fishing), 12 feet of black nylon thread and two needles, a couple of plastic ties, two barbed and one unbarbed fishhook (unbarbed doubles as a suture needle), butterfly bandages, halizone tablets, waterproof matches.
  • Special purpose blades may not be made of metal. Plastic, wood and ceramic knives exist. In most applications, these relatively fragile knives are used to avoid easy detection.

Serrations on a blade "saw" through the item being cut and stay sharp for a long time. The points protect the slicing areas from nicks. A good serration pattern will stay sharp several times as long as a straight edge.

The edge is sharpened at different angles for different purposes. 15 to 25 degrees is a good all-around angle. Slicing knives should have sharper angles, down to ten degrees. Chopping knives need blunter angles, out to thirty degrees.

Sharpening

Knives are sharpened by grinding against a hard rough surface, typically stone, or a soft surface with hard particles, such as sandpaper or a razor strap. The smaller the angle between the blade and stone, the sharper the knife will be, but the less side force is needed to bend the edge over or chip it off. Very sharp knives sharpen at 10 degrees. Typical knives sharpen at 15 degrees. Knives that require a tough edge (such as those that chop) sharpen at 20 degrees. For an extremely durable edge (such as a chisel or drawknife), blades can be sharpened to 30 degrees. In general, the harder the material to be cut the higher the angle of the edge. The composition of the stone affects the sharpness of the blade (finer grain produces sharper blades), as does the composition of the blade (some metals take/keep an edge better than others).

Clamp-style sharpening tools use a clamp with several holes with pre-defined angles. The stone is mounted on a rod and is pulled through these holes, so that the angle remains consistent. Another system is the crock stick setup, where two sticks are put into a plastic or wooden base to form a V shape. When the knife is pulled up the V, the angle is held so long as the blade is held perpendicular to the base.

Honing stones (also called whetstones) come with coarse and fine grits and can be hard or soft describing whether the grit comes free. Arkansas is a traditional source for honing stones, which are traditionally used with water or honing oil. India is another traditional source for stones. Ceramic hones are also common, especially for fine grit size. Water stones (both artificial and natural) come in very fine grits. They are stored in water, and develop a layer of slurry which dulls the edge if the blade is honed as if honing into the stone. Generally, these are more costly than oilstones. Coated hones, which have an abrasive, sometimes diamonds, on a base of plastic or metal are another kind of hone. Sharpening blocks made with corundum are available, but expensive.

Stropping a knife is sometimes a finishing step. This is traditionally done with a leather strap impregnated with abrasive compounds, but can be done on paper, cardstock, or even cloth in a pinch. It will not cut the edge significantly, but produces a very sharp edge with very little metal loss. It is useful when a knife is still sharp, but has lost that 'scary sharp' edge from use.

Other times the final step is done with a steel. This fine process can affect alignment of the edge. Realigning the edge can keep a knife sharp as often a rolled edge will make an otherwise sharp knife dull.

A very sharp knife has an edge that is too small to see with the eye and hard to focus in a microscope. As the knife dulls, a metallic glint can be seen when the edge is held below a bright light. Nicks and rolled edges can also be seen. The shape near the edge can be seen by rotating the knife and watching changes in reflection.

If a knife is used as a scraper or encounters hard particles in softer materials or is used asymmetrically, there may be a sideways load near the tip. In this case the knife should resist bending or breaking.

Legal considerations

Carrying knives in public is forbidden by law in many countries. Exceptions may be made for hunting knives, and for knives used for work-related purposes (e.g. chef's knives). Automatic knives (switchblades) are almost universally banned from civilian carry if not possession. Butterfly knifes (Balisong) are only slightly less stigmatized, and tend to be treated as switchblades by law enforcement agencies due to their connection with gang activity. One exception is Austria, where civilian possession of automatic knives including double-edged automatic OTF ("out The front") daggers is allowed. Most Western European nations are very unfriendly toward all knives other than small pocket knives and similarly small tools, which are also not allowed on commercial aircraft or in certain other venues. Even multitools like the SwissTool, Gerber multitools, and Leatherman multitools are often frowned upon, due to their having relatively large blades and/or locking ability.

Even small knives are forbidden from being carried onboard all commercial airliners, as are almost all items which could potentially be used as weapons, including scissors and nail-clippers. However knives can normally be transported by air travellers if securely packed in hold luggage, where they will be inacessible during the flight. Obviously, travellers should be aware of the legislation affecting knives in the country they are travelling to, which may ban knives which are legal in their home countries. The knife laws of different countries vary, but are generally strict in Western countries.

In the USA

Knife laws vary tremendously. In Texas, for example, individuals may carry knives openly or concealed so long as they are single-edged, and are not daggers, switchblades, or gravity knifes (Butterfly knife legality is questionable — there have been convictions). In some other States, fixed-blade knives are banned, open carry is banned, and sometimes concealed carry of anything except pocket knives is banned. Cities have ordinances further restricting these laws; in San Antonio, TX, it is a violation to carry a folding knife having a locking blade. In some metro areas such as Washington, D.C., going into office buildings or museums, or simply loitering while carrying even small 3" folding knives can be problematic. Other restricted areas in the U.S. include court buildings, federal property (the latter of which technically has a limit of 2.5 inch blades) and public school grounds.

In the UK

Knife possession is legislated in public places, and in private. In private, you can own any type of knife except automatic knives: flick knives, butterfly knives, and switchblades. In general, knives carried in public places are legally considered to be offensive weapons and the carrier can be charged with "possession of an offensive weapon". It is however legal to carry a knife if there is a bona fide reason to do so for example, if it is a tool required for ones trade (e.g. chefs) or if it is part of a national costume (e.g. sgian dubh), or if it is carried for religious reasons (e.g. Sikh Kirpan). A special exception exists for penknives (pocket knives) which are legal without reason for possession, but they must be non-locking and sub 3". Any other article with a blade or point is illegal to possess in a public place, except with a reasonable excuse. Even a folding pocket knife of less than 3" may still be considered an offensive weapon if carried or used for that purpose.

In Japan

With the exception of any type of switchblade, you may carry any knife shorter than 15cm (about 5.9in). To carry knives, the length of blades must be shorter than 6cm (switchblade 5.5cm). (It is strictly prohibited to carry them as defensive weapons.) If people need to carry their knives, they must be concealed and cannot be taken out easily from their sheaths. Japanese Guns and Knives Control Law is relatively tolerant toward knives which can be opened using a single hand. Any type of butterfly knife is legal. With the exception of possessing Japanese Katana, Japanese traditional swords are regarded as offensive weapons. However, if they have artistic values, people may possess one as long as it is registered. If you carry 6cm and longer blade(or deadly), you may receive up to 1 year in prison, or ¥300,000 or about U.S. $2,700 fine.

Knife modifications

Knives can sometimes be customised to the user and/or application:

  • The handle can be altered in shape (for better grip) or material (to prevent electric shock or burns).
  • The surface finish of the blade can be darkened or polished.

Knife superstitions

In some countries it is traditionally believed that the giving of a knife as a gift to a friend will cut or sever the relationship. To avoid such ill luck, the receiver should give a coin in return so as to "pay" for the gift. It is common to include a penny, often taped to the blade, with a knife given as a gift which the receiver is to return as "payment".

Stirring liquids or powders with a knife is considered unlucky; as the rhyme says, "Stir with a knife, stir up strife".

In some cultures giving a knife as a gift is considered a sign of respect and trust. This is especially true in Finland where various non-governmental organizations, clubs and even government agencies traditionally give a puukko (a Finnish fixed-blade hunting/outdoor knife) as a gift to trusted employers or contacts. The puukko is always presented handle first as a sign of trust and friendly intentions.

In many places in the United States it is considered bad luck to hand an open, folding blade knife to someone. This is especially true in more rural areas where carrying a pocket knife is as common as carrying a set of keys. This most likely stems from the fact that it is just not a safe thing to do. It is also believed that allowing someone to close a folding blade knife that you have opened is bad luck.

Just as with swords, several purported superstitions exist regarding the treatment of knives that are used in combat. In general, these superstitions state that it is bad luck to return such a knife from its sheath without using it to draw blood. In some cases, these supposed superstitions are associated with a particular ethnic group or nationality- such a myth exists, for instance, surrounding drawing a sgian dubh without drawing the blood of an Englishman. In many cases, these purported superstitions may not actually exist, but are rather an attempt to discredit or tarnish the reputation of those who the myth concerns.

Certain cultures believe that a knife does not belong to an individual until it has 'bit' them, or tasted their blood. Believers in such superstitions may intentionally prick a finger on the blade of a knife rather than risk a later, accidental cut. According to this superstition, the knife will stay sharp longer and is less likely to accidentally cut its owner once it has tasted his or her blood.

Further reading

References

  1. ^ http://www.agrussell.com/knife_information/knife_encyclopedia/articles/blood_groove.html
  2. ^ by Razor Edge Systems, described in their book "The Razor Edge Book of Sharpening".

See also

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