Coltello

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Il coltello è un utensile di uso manuale utilizzato per il taglio. Solitamente consiste in una lama ad una punta con uno o più bordi affilati fissata ad una maniglia. Le lame sono state utilizzate come attrezzi ed armi dall'età di pietra, all' alba dell' umanità. Gli esperti riconoscono la lama come uno dei primi attrezzi progettati dagli esseri umani per sopravvivere.

Le prime lame erano di silice o di altra roccia, scheggiata o levigata ad un bordo, a volte dotato di una maniglia. Più tardi con gli sviluppi della fusione e della metallurgia le lame sono state sostituite dal bronzo, il ferro, e infine dall'acciaio.

Mentre i materiali sono cambiati con il tempo il disegno di base rimane lo stesso. Insieme alla forchetta ed al cucchiaio, il coltello è stato un utensile comune di largo consumo nel mondo occidentale almeno dal Medio Evo. Oggi la maggior parte delle lame taglienti sono utilizzate in cucina. Nei coltelli a serramanico o " folder " e multi-lama da tasca sono trasportati comunemente, per essere disponibili dovunque. L'importanza dei coltelli come arma è declinata mentre le armi specializzate sono state sviluppate, comunque le lame rimangono un attrezzo universale.

Indice 1 Anatomia di un coltello 1.1 Lame 1.1.1 Materiali 1.1.2 Disegno 2 Tipi di coltello 2.1 Forma 2.2 Funzioni 2.2.1 Uso in casa 2.2.2 Uso Fuori-casa 2.3 Affilatura 3 Considerazioni legali 3.1 Negli Stati Uniti 3.2 In Inghilterra 3.3 In Giappone 4 Altre particolarità dei coltelli 5 Superstizioni sui coltelli

[modifica] Anatomia di un coltello

Un coltello consiste in una lama, di un codolo, di un ramo di guardia e di una impugnatura. La lama è un'estensione del ramo di guardia inserito nell'impugnatura. Il sostegno funziona come un punto e handguard dell'equilibrio, per impedire alle barrette di slittare sulla lamierina. La lamierina a sua volta consiste di una punta, di una spina, di un bordo e di un tallone. Un più pieno, a volte denominato una grondaia di anima o una scanalatura di anima, è una scanalatura dal lato, lungo una lamierina. Secondo un mito popolare, lascia lo spurgo accadere da un'arteria senza rimuovere la lama. In realtà, la funzione è fare l'accenditore delle spade e delle lame mentre sacrifica poca resistenza; sulla maggior parte delle lame ha valore più decorativo. Ulteriormente, una scanalatura sulla lamierina può ridurre la tensione superficiale fra la lamierina e l'articolo che sono tagliati, quindi permettendo il movimento o la rimozione più facile della lamierina. [1] Alcune lame inoltre hanno una spalla in cui la lamierina si ispessisce mentre viene a contatto della maniglia. Nell'affondo, questo aiuta la conservazione la lama dall'incepparsi, per esempio in un osso. In lame da cucina, mantiene gli articoli tagliati dallo spostarsi indietro verso la mano. La maniglia di una lama dovrebbe essere fatta di un materiale antisdrucciolevole. Per una grande lama, è desiderabile che la maniglia sia a strati e che le sue barrette vengano a contatto appena della sua palma quando la lama è afferrata strettamente. Un foro alla fine delle maniglie permette che la lama sia appesa o disposta su una cordicella.

[modifica] Lame

Forschner/Victorinox costruisce coltelli da cucina economici; costruttori di coltelli di alta qualità sono Wüsthof, Global, Henckels, Kershaw Knives e Böker (Tree Brand).

[modifica] Materiali

Le lame dei coltelli sono normalmente di acciaio. Tutto l'acciaio per coltelli è temprato, ossia martensite costituita da una struttura cristallina molto fine con irregolarità del reticolo cristallino che indurisce il materiale. Si forma per rapido raffreddamento in acqua od olio di acciaio portato ad alta temperatura; a queste temperature l'acciaio assume la struttura cristallina austenitica e, per effetto del rapido raffreddamento passa alla struttura martensitica, molto dura ma fragile. Per ridurne la fragilità, la lama viene sottoposta al processo di distensione che consiste nel riscaldare nuovamente la lama ad una temperatura inferiore a quella di tempra per un tempo adeguato e raffreddandola in maniera meno violenta. L'acciaio per coltelli ha un basso contenuto di nichel, perché questo elemento tende a stabilizzare l'austenite anche a basse temperature. Gli acciai con alto contenuto di carbonio, ma basso di cromo forniscono lame molto dure, ma che arrugginiscono e vanno soggette a corrosione localizzata di tipo pitting se non vengono mantenute asciutte ed oliate.

I coltelli in acciaio inox hanno guadagnato molta popolarità a partire dalla seconda metà del XX secolo. L'acciaio inox per coltelli è acciaio con un tenore in cromo molto elevato (12-18% peso), associato ad un alto tenore di carbonio e ad un relativamente basso contenuto di nichel. L'acciaio inox è molto resistente alla corrosione (sebbene quello per coltelli sia meno resistente dell'acciaio a maggior contenuto di nichel) perché cromo e nichel formano degli ossidi molto stabili; tali ossidi formano una pellicola superficiale che impedisce un ulteriore attacco.

L'acciaio inox solitamente contiene particelle di cromo (o di altre leghe metalliche), carburo. Questo acciaio è famoso perchè ha una durata superiore agli altri (i carburi sono più duri del metallo), è più difficile da affilare ed arrugginisce con più difficoltà, low alloy ("carbon") steel (le stesse parti ceramiche non possono essere affilate facilmente.), nonostante i test dimostrino che i coltelli in acciaio inossidabile mantengano il filo meglio dell'acciaio normale.^[1] 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.

Una buona varietà di acciai esotici può essere usata per la fabbricazione delle lame; altri materiali possono essere utilizzati, nonostante questi siano molto meno comuni delle lame in acciaio. Fabbricanti di coltelli come Spyderco e Benchmade solitamente usano 154CM, VG-10, S30V e CPM440V (conosciuto anche come S60V), as well as high-speed high-hardness tool steels like D2 and M2. Altri fabbricanti utilizzano a volte titanio, cobalto e leghe di cobalto. Tutti e tre sono più duttili dei normali acciai inossidabili, 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.

Alcuni fabbricanti come Kyocera producono lame in ceramica per coltelli da cucina; tali lame si caratterizzano per una maggiore durezza ed una maggiore resistenza del filo di taglio. Il materiale è comunque fragile e si può scheggiare e rompere facilmente. Questi coltelli non possono essere lavati in lavastoviglie, ma solamente a mano.

[modifica] Disegno

Ci sono diversi tipi di forme di lame di coltello; alcune delle più comuni sono le seguenti:

(1) una lama normale ha un filo ricurvo, e l'altro bordo piatto. 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.

(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.

(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.

[modifica] Tipi di coltello

I coltelli possono essere divisi in categorie in base alle diverse forme o utilizzi.

[modifica] Forma

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.

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.

[modifica] Funzioni

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:

[modifica] Uso in casa

• The main indoor use of knives is as piece of cutlery or as kitchen knife in various forms, including:

• 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.

• 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, sometimes made of volcanic glass.
• 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.

[modifica] Uso Fuori-casa

• 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.

• 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.

• 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.

[modifica] Affilatura

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.

[modifica] Considerazioni legali

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.

[modifica] Negli Stati Uniti

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.

[modifica] In Inghilterra

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. [1]Even a folding pocket knife of less than 3" may still be considered an offensive weapon if carried or used for that purpose.

[modifica] In Giappone

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.

[modifica] Altre particolarità dei coltelli

I coltelli possono essere modificati per rendere più facile il loro uso:

• 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.

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[modifica] Superstizioni sui coltelli

In alcuni paesi si crede tradizionalmente che dare un coltello come regalo ad un amico tagli o divida il rapporto. Per evitare tale sfortuna chi lo riceve deve dare una moneta in cambio in modo da "pagare" il regalo. È comune includere un centesimo nel regalo di un coltello, chi lo riceve deve restituirlo come "pagamento". Mescolare i liquidi o le polveri con una lama porta sfortuna; come la rima dice, "Mescolar con un coltello, si mesce in sù la disputa".

Per alcune culture dare una lama come regalo è considerato un segno di rispetto e di fiducia. Ciò è pratica comune in particolare in Finlandia dove le varie organizzazioni non governative e perfino gli enti governativi danno tradizionalmente un puukko (un coltello da caccia finlandese dalla lama fissa) come regalo ai datori di lavoro o ai contatti di fiducia.

Il puukko è presentato sempre porgendo l'impugnatura come segno di fiducia e delle intenzioni amichevoli.

In molti posti negli Stati Uniti si considera come porta sfortuna il passare una lama aperta di un serramanico a qualcuno. Ciò è particolarmente frequente nelle zone rurali dove trasportare una lama nella tasca è comune quanto trasportare un mazzo di chiavi. Inoltre si crede che permettere a qualcuno di chiudere una lama di un coltello pieghevole che qualcun altro aveva aperto porti sfortuna. Queste superstizioni si ritrovano anche con le spade, esistono parecchie dicerie per quanto riguarda il trattamento delle lame che sono utilizzate in combattimento. Generalmente, queste superstizioni dichiarano che porta sfortuna estrarre una lama dal suo fodero senza averla usata. In alcuni casi, queste superstizioni sono associate ad un gruppo etnico particolare o la nazionalità che crede in tal miti, per esempio, circondando disegnando un dubh sgian senza disegnare l'anima di un inglese. In molti casi, queste superstizioni non sono realmente esistenti, ma sono piuttosto un tentativo di screditare o appannare la reputazione di coloro che il mito interessa. Determinate culture credono che una lama non appartenga ad un individuo fino a che "non abbia morso loro", o avuto un assaggio della loro anima. Coloro che credono in tali superstizioni possono pungere intenzionalmente una barretta sulla lamierina di una lama piuttosto che rischiare un taglio successivo e accidentale. Secondo questa superstizione, la lama rimarrà più a lungo tagliente ed è meno probabile che tagli accidentalmente il relativo proprietario una volta fattole assaggiare il sangue di questi.