Wood carving Carved wooden cranes Wood carving is a form of working wood by means of a cutting tool held in the hand (this may be a power tool), resulting in a wooden figure or figurine (this may be abstract in nature) or in the sculptural ornamentation of a wooden object. The phrase may also refer to the finished product, from individual sculptures, to hand-worked mouldings composing part of a tracery. For a complete history of wood carving, see history of wood carving. Some of the finest extant examples of early wood carving are from the Middle Ages in Italy and France,[citation needed] where the typical themes of that era were Christian iconography. In England many complete examples remain from the 16th and 17th century, where oak was the preferred medium in this case Wood carving of a hobo by Carl Johan Trygg Figural carving seems to have been widespread. The carving to represent one's god in a tangible form finds expression in numberless ways. The early carver, and, for that matter, the native of the present day, has found a difficulty in giving expression to the eye, and at times has evaded it by inlaying this feature with colored material. • Methods and styles of wood carving • Chip carving • Relief carving • Scandinavian flat-plane • Caricature carving • Love spoon • Treen • Whittling Techniques of carving (plastos) "molded" [1] [2]. It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extruded into an enormous variety of shapes— such as films, fibers, plates, tubes, bottles, boxes, and much more. The common word "plastic" should not be confused with the technical adjective "plastic", which is applied to any material which undergoes a permanent change of shape (a "plastic deformation") when strained beyond a certain point. Aluminum, for instance, is "plastic" in this sense, but not "a plastic" in the common sense; while some plastics, in their finished forms, will break before deforming — and therefore are not "plastic" in the technical sense. There are two main types of plastics, thermoplastic and thermoset. Thermoplastics, if exposed to heat, will melt in two to five minutes. Thermosets will keep their shape until they are a charred, smoking mess. Some examples of thermoplastics are grocery bags, piano keys and some automobile parts. Examples of thermosets are kid's dinner sets and jet skis. • Overview Plastics can be classified by their chemical structure, namely the molecular units that make up the polymer's backbone and side chains. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, e.g. as condensation, polyaddition, cross-linking, etc. Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural, biodegradable, electrically conductive, etc. Plastics can also be ranked by various physical properties, such as density, tensile strength, glass transition temperature, resistance to various chemical products, etc. Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials—such as wood, stone, horn and bone, leather, paper, metal, glass and ceramic—in most of their former uses. The use of plastics is constrained chiefly by their organic chemistry, which seriously limits their hardness, density, and their ability to resist heat, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt or decompose when heated to a few hundred celsius. While plastics can be made electrically conductive to some extent, they are still no match for metals like copper or aluminum. Plastics are still too expensive to replace wood, concrete and ceramic in bulky items like ordinary buildings, bridges, dams, pavement, railroad ties, etc. Chemical structure Common thermoplastics range from 20,000 to 500,000 in molecular mass, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as "repeat units", derived from "monomers"; each polymer chain will have several thousand repeat units. The vast majority of plastics are composed of polymers of carbon and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in the backbone. (Some of commercial interest are silicon based.) The backbone is that part of the chain on the main "path" linking a large number of repeat units together. To vary the properties of plastics, both the repeat unit with different molecular groups "hanging" or "pendant" from the backbone, (usually they are "hung" as part of the monomers before linking monomers together to form the polymer chain). This customization by repeat unit's molecular structure has allowed plastics to become such an indispensable part of twenty first-century life by fine tuning the properties of the polymer. (LDPE), and high density polyethylene (HDPE). PEs are cheap, flexible, durable, and chemically resistant. LDPE is used to make films and packaging materials, while HDPE is used for containers, plumbing, and automotive fittings. While PE has low resistance to chemical attack, it was found later that a PE container could be made much more robust by exposing it to fluorine gas, which modified the surface layer of the container into the much tougher polyfluoroethylene. Polyethylene would lead after the war to an improved material, Polypropylene (PP), which was discovered in the early 1950s by Giulio Natta. It is common in modern science and technology that the growth of the general body of knowledge can lead to the same inventions in different places at about the same time, but polypropylene was an extreme case of this phenomenon, being separately invented about nine times. The ensuing litigation was not resolved until 1989. Polypropylene managed to survive the legal process and two American chemists working for Phillips Petroleum, J. Paul Hogan and Robert Banks, are now generally credited as the "official" inventors of the material. Polypropylene is similar to its ancestor, polyethylene, and shares polyethylene's low cost, but it is much more robust. It is used in everything from plastic bottles to carpets to plastic furniture, and is very heavily used in automobiles. Polyurethane (PU) was invented by Friedrich Bayer & Company in 1937, and would come into use after the war, in blown form for mattresses, furniture padding, and thermal insulation. It is also one of the components (in non-blown form) of the fiber spandex. In 1939, IG Farben filed a patent for polyepoxide or epoxy. Epoxies are a class of thermoset plastic that form cross-links and cure when a catalyzing agent, or hardener, is added. After the war they would come into wide use for coatings, adhesives, and composite materials. Composites using epoxy as a matrix include glass-reinforced plastic, where the structural element is glass fiber, and carbon-epoxy composites, in which the structural element is carbon fiber. Fiberglass is now often used to build sport boats, and carbon-epoxy composites are an increasingly important structural element in aircraft, as they are lightweight, strong, and heat resistant. Two chemists named Rex Whinfield and James Dickson, working at a small English company with the quaint name of the "Calico Printer's Association" in Manchester, developed polyethylene terephthalate (PET or PETE) in 1941, and it would be used for synthetic fibers in the postwar era, with names such as polyester, dacron, and "Terylene". PET is less gas-permeable than other low-cost plastics and so is a popular material for making bottles for Coca-Cola and other carbonated drinks, since carbonation tends to attack other plastics, and for acidic drinks such as fruit or vegetable juices. PET is also strong and abrasion resistant, and is used for making mechanical parts, food trays, and other items that have to endure abuse. PET films are used as a base for recording tape. One of the most impressive plastics used in the war, and a top secret, was polytetrafluoroethylene (PTFE), better known as Teflon, which could be deposited on metal surfaces as a scratch-proof and corrosion-resistant, low-friction protective coating. The polyfluoroethylene surface layer created by exposing a polyethylene container to fluorine gas is very similar to Teflon. A Du Pont chemist named Roy Plunkett discovered Teflon by accident in 1938. During the war, it was used in gaseous-diffusion processes to refine uranium for the atomic bomb, as the process was highly corrosive. By the early 1960s, Teflon adhesion-resistant frying pans were in demand. Teflon was later used to synthesize the breathable fabric Gore-Tex, which can be used to manufacture wet weather clothing that is able to "breathe". Its structure allows water vapour molecules to pass, while not permitting water as liquid to enter. Gore-Tex is also used for surgical applications such as garments and implants; Teflon strand is used to make dental floss; and Teflon mixed with fluorine compounds is used to make decoy flares dropped by aircraft to distract heat-seeking missiles. After the war, the new plastics that had been developed entered the consumer mainstream in a flood. New manufacturing techniques were developed, using various forming, molding, casting, and extrusion processes, to churn out plastic products in vast quantities. American consumers enthusiastically adopted the endless range of colorful, cheap, and durable plastic gimmicks being produced for new suburban home life. One of the most visible parts of this plastics invasion was Earl Tupper's Tupperware, a complete line of sealable polyethylene food containers that Tupper cleverly promoted through a network of housewives who sold Tupperware as a means of bringing in some money.