A knife is a sharp-edged hand tool used for cutting. A knife usually consists of a blade (usually less than 30cm in length) attached to a handle. The blade of a knife is usually pointed and may have one or two cutting edges. Knives have been used as weapons and tools since the Stone Age.
The first knives were flint or other rocks (geology), 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 West since the Middle Ages. In the West, multi-purpose pocket knife are probably the most common knives carried today, and the importance of the knife as a weapon is declining.
A knife consists of a blade, a tang and a handle. The tang is an extension of the blade into the handle. Some knives have a handguard, so that fingers cannot slip onto the edge and be cut.
A blood groove or fuller is a groove up the side of 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 larger knives and swords lighter; on most knives its function is purely decorative.
Some knives also have a shoulder in which the blade thickens as it meets the handle. This helps keep the knife from jamming in bone. In kitchen knives, it keeps chopped items from moving back toward the hand.
The handle of a large knife should be made of a non-slip material, such as Kraton, and should be thick enough that one's fingers just meet one's palm when the knife is gripped as tightly as possible. A hole in the end of the handles allows the knife to be hung or placed on a lanyard.
Blades are usually either stainless or high-carbon steel, though there are a few knives using materials like high tech ceramic and titanium, but these are very uncommon. Stainless steels have gained popularity in the latter half of the twentieth century because they are highly resistant to corrosion (though they can rust under extreme conditions). There's a trade-off between edge-holding and resistance to corrosion, but newer semi-stainless steels like D2 may offer the best compromise. Modern stainless steels include S30V, 154CM, ATS-34, 440C, though . Chromium is the major alloying element in stainless steels, it causes them to be 'stainless'.
High carbon steels, as their name implies are a high carbon, low chromium alloy, and are very prone to rust and pitting if not kept dry. They are generally used for their excellent edge-holding ability.
As of 2004 there are a variety of exotic steels and other materials used to form blades. Knife manufacturers such as Spyderco and Benchmade typically use 154CM, VG-10, S30V, and CPM440V, as well as several high-speed high-hardness tool steels like D2 and M2. Other manufacturers sometimes use titanium, stellite, talonite, and other 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 the latter two alloys' cobalt content. Damascus steel, which is layered and instantly recognizable by its beautiful patterns, is typically used in high-end knife blades and has respectable edge retention. There is typically more demand for stainless steels and exotic alloys in the utility, outdoor, and tactical knife categories than there is in the kitchen knife category.
Kitchen knife blades tend to fall into two categories. Some use stainless steels to prevent users from having to pamper their blades and to be more forgiving on those who put chefs' knives in the dishwasher. Others are high in carbon for edge-holding ability, the presumption being that kitchens are not the wilderness and that chefs are willing to clean knives properly in exchange for better edge retention. Forschner/Victorinox makes decent cheap kitchen knives; higher-end manufacturers include Wustoff, Global, and Henckels. Some manufacturers, particularly of kitchen knives, make ceramic blades; these stay sharp longer but due to their hardness chip more readily, and an accidental drop may chip, crack, or shatter the blade.
There are several basically different types of knife blades: normal, spey, clipped, sheeps-foot, tanto and ulu.
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A normal (1) blade has a curving edge, and flat back. A dull back lets one use fingers to concentrate force, and makes the knife heavier and stronger for its size. The curve concentrates force, making cutting easier. Therefore, it can chop as well as pick and slice. A curved or trailing-point (2) 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. A Double edged (3) blade has two edges. The idea is to make a blade that cuts in either direction, with a strong sharp point. It's used for fighting knives (dagger, bayonets) because it can cut in both directions, has a sharp point and is strong. A clip point (4) 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 knifes effectiveness in fighting. This is another favourite blade shape. The Bowie knife is a clipped blade that's good for fighting, and strong. A sheepsfoot (5) knife has a straight edge, and a curved dull back. It give the most control, because the back, dull edge is made to be held by fingers. It's good for whittling, including sheep's hooves. A tanto style (6) knife is thick. It is superficially similar to the points on most Japanese long and short swords (katana and wakizashi), although is a bit of a misnomer as the traditional Japanese tanto (dagger) does not share this point style. The edge is straight. The point is actually a second edge on the end of the blade, swept back from the point at 80-60 degrees. |
An ulu knife is a sharpened half-circle. It's all edge, with no point, and a handle in the middle. It's good for scraping, and sometimes chopping. It is the strongest knife-shape.
A drop-point blade is very similar to a clip point, but it features the black convexed down, rather than having a clip taken out of it. It's handing characteristics and overall form is very similar to the clip-point.
For whittling (artistic wood carving) a blade as short as 25mm (1 inch) is common.
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.
Knives can be categorized based on either form or function.
Knives exist in several styles:
In general, knives are either working, or everyday use blades, or fighting knives. Some knives, such as the Scottish Dirk and Japanese Tanto function in both roles. Many knives are specific to a particular activity or occupation:
A sharp knife is a safe knife. Dull knives lead to excessive use of force to cut materials, increasing the chance that the blade may slip and the force will be transferred to an unintended destination such as yourself or another person or object. In Boy Scout parlance, an area within the radius of the arm and blade length combined is called the 'blood circle'. Also, a dull or damaged knife will inflict a worse wound than a relatively 'clean' cut from a sharp knife.
Knives proffered to another person should always be offered handle first.
A knife should be kept clean, dry and sharp. Steel blades rust easily, but oiling will prevent pitting due to oxidation and tarnish. Most knives are not intended as pry bars or screwdrivers. Either use is likely to break off the tip of the blade, or to bend or break the knife beyond repair. Most high quality knives are also tempered very hard, so that they will retain an edge longer. However, this also makes them brittle.
Knives are sharpened by grinding against a hard surface, typically stone. The smaller the angle between the blade and stone, the sharper the knife will be, but the faster it will dull. A guide is very helpful. Very sharp knives sharpen at 12-15 degrees. Typical knives sharpen at 22 degrees. Knives that chop may sharpen at 25 degrees. In short, 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).
Examples of sharpening tools are the clamp-style systems, which 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 variant is the crock stick setup, where two sticks are put into a plastic or wooden base to form a V shape. When you pull a knife up the V, the angle is held for you, as long as you hold the blade perpendicular to the base.
Remove a wire edge (burr) if one forms during sharpening. Use a slighly steeper angle with very light pressure to do so. If not removed, it will break off in use, and the knife will instantly become dull. An alternate method of removing a wire edge is stroking from side to side on a very fine stone, using light strokes. This will flip the burr back and forth as it is ground off.
To feel for a wire edge, move your thumb lightly across the edge. It should come off with no resistance. If you feel a little bit of pull at the edge or the nail is sightly abraided, you may have a wire burr.
Traditional stones are arkansas stones, which come in soft (coarse) and hard (fine) varieties. These are traditionally used with water or honing oil, but any oil compound, including olive oil, will do. India stones are also similar to arkansas stones in function and end result.
Ceramic stones are also used very often. Unlike natural stones, they will not wear, and are very often used without any type of oil.
Water stones (both artificial and natural) come in very fine grits. They are stored in water, and develop a layer of slurry which helps polish off the edge. Generally, these are more costly than oilstones. Needless to say, oil should not be used on these.
Oil is used to lift the metal dust, called swarf, off the stone. This is usually recommended for natural stones, but some say that detergent and a brillo pad will have the same effect. Ceramic stones do not need oil, they can be cleaned off with detergent. Diamond stones should NOT be used with oil, rather, they can be washed off with water.
The best sharpening stones are industrial diamonds embedded in plastic or metal. These are more expensive, but still affordable. They cut about twice as fast as other stones. Also popular, and rather expensive, are sharpening blocks made from corundum.
Stropping a knife is an excellent 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.
Steeling isn't actually sharpening nor honing. All you are doing with a sharpening steel is realigning the edge. Realigning the edge goes a long way in keeping the knife sharp, as often times, a rolled edge will make an otherwise sharp knife dull. There is no reason to remove excess metal if the edge can be fixed with several strokes on a sharpening steel.
Even small knives are forbidden on all commercial airliners and are among the illegal imports that may be confiscated at airports by customs staff even if packed in luggage. The knife laws of different countries vary, but are generally strict in Western countries.
Knife laws in U.S. cities 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 knives (balisong 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 pocketknives 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, carrying even small 3" folding knives can be problematic. Other restricted areas in the U.S. include court buildings and federal property (the latter of which technically has a limit of 2" for blades).
Carrying knives in public is generally 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. Balisongs (butterfly knives) are only slightly less stigmatized, and tend to be treated as switchblades by unfriendly law enforcement agencies. Most Western European nations are very unfriendly toward all knives other than small pocket knives and similarly small tools, which are nonetheless not allowed on planes 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.
Knives can be sometimes be customised to the user and/or application:
"Knives" is also an episode of the science-fiction television series Babylon 5; see Knives (Babylon 5).
As a verb, to knife is to use a knife to injure or kill by stabbing, slashing, or otherwise using the sharp edge of the knife as a weapon.
