paint

Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. It is most commonly used to add color and/or texture to objects. History Cave paintings drawn with red and yellow ochre, hematite, manganese oxide, and charcoal may have been made by early Homo sapiens as long as 40,000 years ago. Ancient colored walls at Dendera, Egypt, which were exposed for many ages to the open air, still possess a perfect brilliancy of color, as vivid as when they were painted about 2,000 years ago. The Egyptians mixed their colors with some gummy substance, and applied them separated from each other without any blending or mixture. They appeared to have used six colors: white, black, blue, red, yellow, and green. They first covered the field entirely with white, upon which they traced the design in black, leaving out the lights of the ground color. They used minium for red, and generally of a dark tinge. Pliny mentions some painted ceilings in his day in the town of Ardea, which had been executed at a date prior to the foundation of Rome. He expresses great surprise and admiration at their freshness, after the lapse of so many centuries. Paint was made with the yolk of eggs and therefore, the substance would harden and stick onto the surface applied. Pigments were made from plants, sands, and different soil types Components Pigment Pigments are granular solids incorporated into the paint to contribute color, toughness, texture or simply to reduce the cost of the paint. Alternatively, some paints contain dyes instead of or in combination with pigments. Pigments can be classified as either natural or synthetic types. Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics would include engineered molecules, calcined clays, blanc fix, precipitated calcium carbonate, and synthetic pyrogenic silicas. Hiding pigments, in making paint opaque, also protect the substrate from the harmful effects of ultraviolet light. Hiding pigments include titanium dioxide, phthalo blue, red iron oxide, and many others. Fillers are a special type of pigment that serve to thicken the film, support its structure and simply increase the volume of the paint. Fillers are usually made of cheap and inert materials, such as diatomaceous earth, talc, lime, barytes, clay, etc. Floor paints that will be subjected to abrasion may even contain fine quartz sand as a filler. Not all paints include fillers. On the other hand some paints contain very large proportions of pigment/filler and binder.

Some pigments are toxic, such as the lead pigments that are used in lead paint. Paint manufacturers began replacing white lead pigments with the less toxic substitute, titanium white (titanium dioxide), even before lead was functionally banned in paint for residential use in 1978 by the U.S. Consumer Product Safety Commission. The titanium dioxide used in most paints today is often coated with silica or alumina for various reasons such as better exterior durability, or better hiding performance (opacity) via better efficiency promoted by more optimal spacing within the paint film. Binder, vehicle, or resins The binder, commonly referred to as the vehicle, is the actual film forming component of paint. It is the only component that must be present; other components listed below are included optionally, depending on the desired properties of the cured film. The binder imparts adhesion, binds the pigments together, and strongly influences such properties as gloss potential, exterior durability, flexibility, and toughness. Binders include synthetic or natural resins such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene (VAE), polyurethanes, polyesters, melamine resins, epoxy, or oils. Binders can be categorized according to drying, or curing mechanism. The four most common are simple solvent evaporation, oxidative crosslinking, catalyzed/cross linked polymerization, and coalescence. There are others. Note that drying and curing are two different processes. Drying generally refers to evaporation of the solvent or thinner,[1] whereas curing refers to polymerization of the binder. (The term "vehicle" is industrial jargon which is used inconsistently, sometimes to refer to the solvent and sometimes to refer to the binder.) Depending on chemistry and composition, any particular paint may undergo either, or both processes. Thus, there are paints that dry only, those that dry then cure, and [2] those that do not depend on drying for curing. Paints that dry by simple solvent evaporation and contain a solid binder dissolved in a solvent are known as lacquers. A solid film forms when the solvent evaporates, and because the film can re-dissolve in solvent, lacquers are not suitable for applications where chemical resistance is important. Classic nitrocellulose lacquers fall into this category, as do non-grain raising stains composed of dyes dissolved in solvent and more modern acrylic based coatings such as 5-ball Krylon aerosol. Performance varies by formulation, but lacquers generally tend to have better UV resistance and lower corrosion resistance than comparable systems that cure by polymerization or coalescence. Latex paint is a water-borne dispersion of sub-micrometre polymer particles. The term "latex" in the context of paint simply means an aqueous dispersion; latex rubber (the sap of the rubber tree that has historically been called latex) is not an ingredient. These dispersions are prepared by emulsion polymerization. Latex paints cure by a process called

coalescence where first the water, and then the trace, or coalescing, solvent, evaporate and draw together and soften the latex binder particles and fuse them together into irreversibly bound networked structures, so that the paint will not redissolve in the solvent/water that originally carried it. Residual surfactants in the paint as well as hydrolytic effects with some polymers cause the paint to remain susceptible to softening and, over time, degradation by water. Paints that cure by oxidative crosslinking are generally single package coatings. When applied, the exposure to oxygen in the air starts a process that crosslinks and polymerizes the binder component. Classic alkyd enamels would fall into this category. Oxidative cure coatings are catalyzed by metal complex driers such as cobalt naphthenate. Paints that cure by "catalyzed" polymerization are generally two package coatings that polymerize by way of a chemical reaction initiated by mixing resin and curing agent/hardener, and which cure by forming a hard plastic structure. Depending on composition they may need to dry first, by evaporation of solvent. Classic two package epoxies or polyurethanes would [2] fall into this category. The word catalyst is a misnomer as catalyst should not be part of the polymer. Cobalt driers are catalysts, iso cyanates and epoxy adducts are not.[citation needed] There are paints called plastisols/organosols, which are made by blending PVC granules with a plasticiser. These are stoved and the mix coalesceses. Still other films are formed by cooling of the binder. For example, encaustic or wax paints are liquid when warm, and harden upon cooling. In many cases, they will resoften or liquify if reheated. Recent environmental requirements restrict the use of Volatile Organic Compounds (VOCs), and alternative means of curing have been developed, particularly for industrial purposes. In UV curing paints, the solvent is evaporated first, and hardening is then initiated by ultraviolet light. In powder coatings there is little or no solvent, and flow and cure are produced by heating of the substrate after electrostatic application of the dry powder. Solvent The main purposes of the solvent are to adjust the curing properties and viscosity of the paint. It is volatile and does not become part of the paint film. It also controls flow and application properties, and affects the stability of the paint while in liquid state. Its main function is as the carrier for the non volatile components. In order to spread heavier oils (i.e. linseed) as in oil-based interior housepaint, a thinner oil is required. These volatile substances impart their properties temporarily²once the solvent has evaporated or disintegrated, the remaining paint is fixed to the surface. This component is optional: some paints have no diluent. Water is the main diluent for water-borne paints, even the cosolvent types.

Solvent-borne, also called oil-based, paints can have various combinations of solvents as the diluent, including aliphatics, aromatics, alcohols, ketones and white spirit. These include organic solvents such as petroleum distillate, esters, glycol ethers, and the like. Sometimes volatile low-molecular weight synthetic resins also serve as diluents. Such solvents are used when water resistance, grease resistance, or similar properties are desired. Additives Besides the three main categories of ingredients, paint can have a wide variety of miscellaneous additives, which are usually added in very small amounts and yet give a very significant effect on the product. Some examples include additives to modify surface tension, improve flow properties, improve the finished appearance, increase wet edge, improve pigment stability, impart antifreeze properties, control foaming, control skinning, etc. Other types of additives include catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, UV stabilizers, flatteners (de-glossing agents), biocides to fight bacterial growth, and the like. Additives normally do not significantly alter the percentages of individual components in a formulation.[3] Color changing paint Various technologies exist for making paints that change color. Thermochromic paints and coatings contain materials that change conformation when heat is applied, and so they change color. Liquid crystals have been used in such paints, such as in the thermometer strips and tapes used in fishtanks. Photochromic paints and coatings contain dyes that change conformation when the film is exposed to UV light, and so they change color. These materials are used to make eyeglasses. Electrochromic paints change color in response to an applied electric current. Car manufacturer Nissan has been reportedly working on an electrochromic paint for use in its vehicles, based on particles of paramagnetic iron oxide. When subjected to an electromagnetic field the paramagnetic particles change spacing, modifying their color and reflective properties. The electromagnetic field would be formed using the conductive metal of the car body.[4] Electrochromic paints can be applied to plastic substrates as well, using a different coating chemistry. The technology involves using special dyes that change conformation when an electric current is applied across the film itself. Recently, this new technology has been used to achieve glare protection at the touch of a button in passenger airplane windows. Art Since the time of the Renaissance, siccative (drying) oil paints, primarily linseed oil, have been the most commonly used kind of paints in fine art applications; oil paint is still common today. However, in the 20th century, water-based paints, including watercolors and acrylic paints, became very popular with the development of acrylic and other latex paints. Milk paints (also called casein), where the medium is derived from the natural

emulsion that is milk, were popular in the 19th century and are still available today. Egg tempera (where the medium is an emulsion of egg yolk mixed with oil) is still in use as well, as are encaustic wax-based paints. Gouache is a variety of opaque watercolor which was also used in the Middle Ages and Renaissance for manuscript illuminations. The pigment was often made from ground semiprecious stones such as lapis lazuli and the binder made from either gum arabic or egg white. Gouache, also known as 'designer color' or 'body color' is commercially available today. Poster paint has been used primarily in the creation of student works, or by children. Application Paint can be applied as a solid, a gaseous suspension (aerosol) or a liquid. Techniques vary depending on the practical or artistic results desired. As a solid (usually used in industrial and automotive applications), the paint is applied as a very fine powder, then baked at high temperature. This melts the powder and causes it to adhere (stick) to the surface. The reasons for doing this involve the chemistries of the paint, the surface itself, and perhaps even the chemistry of the substrate (the overall object being painted). This is commonly referred to as "powder coating" an object. As a gas or as a gaseous suspension, the paint is suspended in solid or liquid form in a gas that is sprayed on an object. The paint sticks to the object. This is commonly referred to as "spray painting" an object. The reasons for doing this include:

After liquid paint is applied, there is an interval during which it can be blended with additional painted regions (at the "wet edge") called "open time." The open time of an oil or alkydbased emulsion paint can be extended by adding white spirit, similar glycols such as Dowanol (propylene glycol ether) or commercial open time prolongers. This can also facilitate the mixing of different wet paint layers for aesthetic effect. Latex and acrylic emulsions require the use of drying retardants suitable for water-based coatings. Paint application by spray is the most popular method in industry. In this, paint is atomized by the force of compressed air or by the action of high pressure compression of the paint itself, which results in the paint being turned into small droplets which travel to the article which is to be painted. Alternate methods are airless spray, hot spray, hot airless spray, and any of these with an electrostatic spray included. There are numerous electrostatic methods available. Dipping used to be the norm for objects such as filing cabinets, but this has been replaced by high speed air turbine driven bells with electrostatic spray. Car bodies are primed using cathodic elephoretic primer, which is applied by charging the body depositing a layer of primer. The unchanged residue is rinsed off and the primer stoved. Many paints tends to separate when stored, the heavier components settling to the bottom and require mixing before use. Some paint outlets have machines for mixing the paint by shaking it vigorously in the can for a few minutes. The opacity and the film thickness of paint may be measured using a drawdown card. Water-based paints tend to be the easiest to clean up after using²the brushes and rollers can be cleaned with soap and water. Proper disposal of left over paint is a challenge. Sometimes it can be recycled: Old paint may be usable for a primer coat or an intermediate coat, and paints of similar chemistry can be mixed to make a larger amount of a uniform color. To dispose of paint it can be dried and disposed of in the domestic waste stream provided that it contains no prohibited substances (see container). Disposal of liquid paint usually requires special handling and should be treated as hazardous waste, and disposed of according to local regulations.[5][6] Product variants

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The application mechanism is air and thus no solid object ever touches the object being painted; The distribution of the paint is very uniform so there are no sharp lines; It is possible to deliver very small amounts of paint; A chemical (typically a solvent) can be sprayed along with the paint to dissolve together both the delivered paint and the chemicals on the surface of the object being painted; Some chemical reactions in paint involve the orientation of the paint molecules.

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In the liquid application, paint can be applied by direct application using brushes, paint rollers, blades, other instruments, or body parts such as fingers. Rollers generally have a handle that allows for different lengths of poles which can be attached to alow for painting at different heights. Generally, roller application takes two coats for even color. A roller with a thicker nap is used to apply paint on uneven surfaces. Edges are often finished with an angled brush.

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Primer is a preparatory coating put on materials before painting. Priming ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the material being painted. It can also be used to block and seal stains, or to hide a color that is to be painted over. Emulsion paint is a water-based paint used for painting interior or exterior surfaces.

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Varnish and shellac provide a protective coating without changing the color. They are paints without pigment. Wood stain is a type of paint that is very "thin," that is, low in viscosity, and formulated so that the pigment penetrates the surface rather than remaining in a film on top of the surface. Stain is predominantly pigment or dye and solvent with little binder, designed primarily to add color without providing a surface coating. Lacquer is usually a fast-drying solvent-based paint or varnish that produces an especially hard, durable finish. An enamel paint is a paint that dries to an especially hard, usually glossy, finish. Enamel paints sometimes contain glass powder or tiny metal flake fragments instead of the color pigments found in standard oilbased paints. Enamel paint is sometimes mixed with varnish or urethane to increase shine as well as assist its hardening process. A glaze is an additive used with paint to slow drying time and increase translucency, as in faux painting and Art Painting. A roof coating is a fluid applied membrane which has elastic properties that allows it to stretch and return to their original shape without damage. It provides UV protection to polyurethane foam and is widely used as part of a roof restoration system. Fingerpaint is a kind of paint intended to be applied with the fingers; it typically comes in pots and is used by small children, though it has very occasionally been used by adults either to teach art to children, or for their own independent use. Inks are similar to paints, except they are typically made using finely ground pigments or dyes, and are designed so as not to leave a thick film of binder. Titanium dioxide is extensively used for both house paint and artist's paint, because it is permanent and has good covering power. Titanium dioxide pigment accounts for the largest use of the element. Titanium paint is an excellent reflector of infrared, and is extensively used in solar observatories where heat causes poor seeing conditions. Anti-graffiti coatings are used to defeat the marking of surfaces by graffiti vandals. There are two categories, sacrificial and non-bonding. Sacrificial coatings are clear coatings that allow the removal of graffiti, usually by pressure washing the surface with high-pressure water, removing the graffiti, and the coating (hence, sacrificed). They must be re-applied afterward for continued protection. This is most commonly used on

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natural-looking masonry surfaces, such as statuary and marble walls, and on rougher surfaces that are difficult to clean. Non-bonding coatings are clear, high-performance coatings, usually catalyzed polyurethanes, that allow the graffiti very little to bond to. After the graffiti is discovered, it can be removed with the use of a solvent wash, without damaging the underlying substrate or protective coating. These work best when used on smoother surfaces, and especially over other painted surfaces, including murals.

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Anti-climb paint is a non-drying paint that appears normal while still being extremely slippery. It is usually used on drainpipes and ledges to deter burglars and vandals from climbing them, and is found in many public places. When a person attempts to climb objects coated with the paint, it rubs off onto the climber, as well as making it hard for them to climb.

Dangers Volatile organic compounds (VOCs) in paint are considered harmful to the environment and especially for people who work with them on a regular basis. Exposure to VOCs has been related to organic solvent syndrome, although this relation has been somewhat controversial.[7] In the United States, environmental regulations, consumer demand, and advances in technology led to the development of low-VOC and zero-VOC paints and finishes. These new paints are widely available and meet or exceed the old highVOC products in performance and cost-effectiveness while having significantly less impact on human and environmental health. Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss sheens by the addition of "flatting" agents. Varnish has little or no colour, is transparent, and has no added pigment, as opposed to paints or wood stains, which contain pigment and generally range from opaque to translucent. Varnishes are also applied over wood stains as a final step to achieve a film for gloss and protection. Some products are marketed as a combined stain and varnish. After being applied, the film-forming substances in varnishes either harden directly, as soon as the solvent has fully evaporated, or harden after evaporation of the solvent through certain curing processes, primarily chemical reaction between oils and oxygen from the air (autoxidation) and chemical reactions between components of the varnish. Resin varnishes "dry" by evaporation of the solvent and harden almost immediately upon drying. Acrylic and waterborne varnishes "dry" upon evaporation of the water but experience an extended curing period. Oil, polyurethane, and epoxy varnishes remain liquid even after evaporation of the solvent but quickly begin to cure, undergoing successive stages from liquid or syrupy, to tacky or sticky, to dry gummy, to "dry to the touch", to hard. Environmental factors such as heat and humidity play a very large role in the drying and curing times of

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varnishes. In classic varnish the cure rate depends on the type of oil used and, to some extent, on the ratio of oil to resin. The drying and curing time of all varnishes may be sped up by exposure to an energy source such as sunlight, ultraviolet light, or heat. Many varnishes rely on organic solvents, or on organic oils or resins for their binder; these are highly flammable in their liquid state. All drying oils, certain alkyds, and many single-component polyurethanes produce heat during the curing process. Therefore, oil-soaked rags and paper can smolder or ignite hours after application if they are bunched or piled together, or, for example, placed in a container where the heat cannot dissipate. History Early varnishes were developed by mixing resin, like pine sap, with a solvent and applying them with a brush to get the golden [1] and hardened effect we see in today's varnishes. The ancient Egyptians were acquainted with the art of varnishing, but its origin appears to be far east of there in India, China and Japan, where the practice of lacquer work, a species of varnish application, was known at a very early date. It has been claimed that Japan was acquainted with the art of lacquering by 500 or 600 B.C.E., but the majority of authorities place its first usage there to the 3rd century of our era, as an art acquired from their neighbors the Koreans. The natives of China and India probably knew the art much earlier than the Japanese. Varnish and lacquer work are, however, generally treated in the arts as separate and distinct. Etymology The word "varnish" comes from Latin vernix meaning odorous resin, the etymology of which comes from the Greek Berenice, the ancient name of modern Benghazi in Libya, where the first varnishes were used and where resins from the trees of nowvanished forests were sold. Berenice comes from the Greek words phero (to bring) + nike (victory). Components of Classic Varnish Drying oil There are many different types of drying oil, including linseed oil, tung oil, and walnut oil. These contain high levels of polyunsaturated fatty acids. Resin Resins that are used in varnishes include amber, kauri gum, dammar, copal, rosin (pine resin), sandarac, balsam, elemi, and others. In the 1900s in Canada, resins from local trees were used to finish pianos. As a result these now antique pianos are considered difficult to refinish. However, shellac can be used over the existing resins provided sufficient time is allowed for thin coats to cure. Thus the original finish can be returned to its original lustre while preserving the colour and age related crackle. [edit] Turpentine or solvent Traditionally, natural (organic) turpentine was used as the thinner or solvent, but has been replaced by several mineral based turpentine substitutes such as white spirit or "paint thinner", also known as "mineral spirit".

Types Violin Violin varnishing is a multi-step process involving some or all of the following: primer, sealer, ground, color coats, and clear topcoat. Some systems use a drying oil varnish as described below, while others use spirit (or solvent) varnish. Touchup in repair or restoration is only done with spirit varnish. Drying oil such as walnut oil or linseed oil may be used in combination with amber, copal, rosin or other resins. The oil is prepared by cooking or exposing to air and sunlight. The refined resin is typically available as a translucent solid and is then "run" by cooking or literally melting it in a pot over heat without solvents. The thickened oil and prepared resin are then cooked together and thinned with turpentine (away from open flame) into a brushable solution. Some violin finishing systems use vernice bianca (egg white and gum arabic) as a sealer or ground. Resin Most resin or "gum" varnishes consist of a natural, plant- or insect-derived substance dissolved in a solvent, called spirit varnish or solvent varnish. The solvent may be alcohol, turpentine, or petroleum-based. Some resins are soluble in both alcohol and turpentine. Generally, petroleum solvents, i.e. mineral spirits or paint thinner, can substitute for turpentine. The resins include amber, dammar, copal, rosin, sandarac, elemi, benzoin, mastic, balsam, shellac, and a multitude of lacquers. Synthetic resins such as phenolic resin may be employed as a secondary component in certain varnishes and paints. Over centuries, many recipes were developed which involved the combination of resins, oils, and other ingredients such as certain waxes. These were believed to impart special tonal qualities to musical instruments and thus were sometimes carefully guarded secrets. The interaction of different ingredients is difficult to predict or reproduce, so expert finishers were often prized professionals. Shellac Shellac is a very widely used single component resin varnish that is alcohol soluble. It is not used for outdoor surfaces or where it will come into repeated contact with water such as around a sink or bathtub. The source of shellac resin is a brittle or flaky secretion of the female lac insect, Kerria lacca, found in the forests of Assam and Thailand and harvested from the bark of the trees where she deposits it to provide a sticky hold on the trunk. Shellac is the basis of French polish, which for centuries has been the preferred finish for fine furniture. Specified "dewaxed" shellac has been processed to remove the waxy substances from original shellac and can be used as a primer and sanding-sealer substrate for other finishes such as polyurethanes, alkyds, oils, and acrylics. Prepared shellac is typically available in "clear" and "amber" (or "orange") varieties, generally as "three pound cut" or three pounds dry shellac to one US gallon of alcohol. Other natural color shades such as ruby and yellow are available from

specialty pigment or woodworker's supply outlets. Dry shellac is available as refined flakes, "sticklac," "button lac," or "seedlac." "White pigmented" shellac primer paint is widely available in retail outlets, billed as a fast-drying interior primer "problem solver", in that it adheres to a variety of surfaces and seals off odors and smoke stains. Shellac clean-up may be done either with pure alcohol or with ammonia cleansers. Alkyd Typically, modern commercially produced varnishes employ some form of alkyd for producing a protective film. Alkyds are chemically modified vegetable oils which operate well in a wide range of conditions and can be engineered to speed up the cure rate and thus harden faster. Better (and more expensive) exterior varnishes employ alkyds made from high performance oils and contain UV-absorbers; this improves gloss-retention and extends the lifetime of the finish. Various resins may also be combined with alkyds as part of the formula for typical "oil" varnishes that are commercially available. Spar varnish Spar varnish (also called marine varnish) was originally intended for use on ship or boat spars, to protect the timber from the effects of sea and weather. Spars bend under the load of their sails. The primary requirements were water resistance and also elasticity, so as to remain adhering as the spars flexed. Elasticity was a pre-condition for weatherproofing too, as a finish that cracked would then allow water through, even if the remaining film was impermeable. Appearance and gloss was of relatively low value, in comparison. Modified tung oil and phenolic resins are often used. When first developed, no varnishes had good UV-resistance. Even after more modern synthetic resins did become resistant, a true spar varnish maintained its elasticity above other virtues, even if this required a compromise in its uv-resistance. Spar varnishes are thus not necessarily the best choice for outdoor woodwork which does not need to bend in service. Despite this, the widespread perception of "marine products" as "tough" led to domestic outdoor varnishes being branded as "Spar varnish" and sold on the virtue of their weather- and uvresistance. These claims may be more or less realistic, depending on individual products. Only relatively recently have spar varnishes been available that can offer both effective elasticity and uv-resistance. Drying Oils By definition, drying oils, such as linseed and tung oil, are not true varnishes though often in modern terms they accomplish the same thing. Drying oils cure through an exothermic reaction between the polyunsaturated portion of the oil and oxygen from the air. Originally, the term "varnish" referred to finishes that were made entirely of resin dissolved in suitable solvents, either ethanol (alcohol) or turpentine. The advantage to finishers in previous centuries was that resin varnishes had a very rapid cure rate compared to oils; in most cases they are cured practically as soon as the solvent has fully evaporated. By contrast, untreated or "raw" oils may take weeks or months to cure, depending on ambient temperature and other environmental factors. In modern terms, "boiled" or partially polymerized drying oils with added siccatives or dryers (chemical catalysts) have cure times of less than 24 hours.

However, certain non-toxic by-products of the curing process are emitted from the oil film even after it is dry to the touch and over a considerable period of time. It has long been a tradition to combine drying oils with resins to obtain favourable features of both substances. Polyurethane Polyurethane varnishes are typically hard, abrasion-resistant, and durable coatings. They are popular for hardwood floors but are considered by some[who?] to be difficult or unsuitable for finishing furniture or other detailed pieces. Polyurethanes are comparable in hardness to certain alkyds but generally form a tougher film. Compared to simple oil or shellac varnishes, polyurethane varnish forms a harder, decidedly tougher and more waterproof film. However, a thick film of ordinary polyurethane may de-laminate if subjected to heat or shock, fracturing the film and leaving white patches. This tendency increases with long exposure to sunlight or when it is applied over soft woods like pine. This is also in part due to polyurethane's lesser penetration into the wood. Various priming techniques are employed to overcome this problem, including the use of certain oil varnishes, specified "dewaxed" shellac, clear penetrating epoxy sealer, or "oil-modified" polyurethane designed for the purpose. Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher "build" of film, accomplishing in two coats what may require multiple applications of oil. Polyurethane may also be applied over a straight oil finish, but because of the relatively slow curing time of oils, the emission of certain chemical byproducts, and the need for exposure to oxygen from the air, care must be taken that the oils are sufficiently cured to accept the polyurethane. Unlike drying oils and alkyds which cure, after evaporation of the solvent, upon reaction with oxygen from the air, true polyurethane coatings cure after evaporation of the solvent by a variety of reactions of chemicals within the original mix, or by reaction with moisture from the air. Certain polyurethane products are "hybrids" and combine different aspects of their parent components. "Oil-modified" polyurethanes, whether water-borne or solvent-borne, are currently the most widely used wood floor finishes. Exterior use of polyurethane varnish may be problematic due to its heightened susceptibility to deterioration through ultraviolet light exposure. All clear or translucent varnishes, and indeed all film-polymer coatings (e.g. paint, stain, epoxy, synthetic plastic, etc.), are susceptible to this damage in varying degrees. Pigments in paints and stains protect against UV damage. UV-absorbers are added to polyurethane and other varnishes (e.g. spar varnish) to work against UV damage but are decreasingly effective over the course of 2±4 years, depending on the quantity and quality of UV-absorbers added as well as the severity and duration of sun exposure. Water exposure, humidity, temperature extremes, and other environmental factors affect all finishes. By contrast, wooden items retrieved from the Egyptian pyramids have a new and [citation needed] . Even fresh appearance after 4000 years of storage there, however, fungal colonies were present, and mildew and fungus are another category of entities which attack varnish. In other words, the only coat of varnish with near perfect durability is the one stored in a vacuum, in darkness, at a low and unvarying temperature. Otherwise, care and upkeep are required.

Lacquer The word lacquer refers to quick-drying, solvent-based varnishes or paints. Although their names may be similarly derived, lacquer is not the same as shellac and is not dissolved in alcohol. Lacquer is dissolved in lacquer thinner, which is a highly-flammable solvent typically containing butyl acetate and xylene or toluene. Lacquer is typically sprayed on, within a spray booth that evacuates overspray and minimizes the risk of combustion. Outside America, the rule of thumb is that a clear wood finish formulated to be sprayed is a lacquer but if it is formulated to be brushed on then it is a varnish. Thus the vast majority of wooden furniture is lacquered. Acrylic Acrylic varnishes are typically water-borne varnishes with the lowest refractive index of all finishes and high transparency. They resist yellowing. Acrylics have the advantage of water clean-up and lack of solvent fumes, but typically do not penetrate into wood as well as oils. They sometimes lack the brushability and self-levelling qualities of solvent-based varnishes. Generally they have good UV-resistance. In the art world, varnishes offer dust-resistance and a harder surface than bare paint ± they sometimes have the benefit of ultraviolet light resistors, which help protect artwork from fading in exposure to light. Acrylic varnish should be applied using an isolation coat (a permanent, protective barrier between the painting and the varnish, preferably a soft, glossy gel medium) to make varnish removal and overall conservation easier. Two-Part Various epoxies have been formulated as varnishes or floor finishes whereby two components are mixed directly before application. Often, the two parts are of equal volume and are referred to as "part A" and "part B". True polyurethanes are two-part systems. All two-part epoxies have a "pot-life" or "working time" during which the epoxy can be used. Usually the pot-life is a matter of a few hours but is also highly temperature dependent. Both water-borne and solvent based epoxies are used. Conversion Used when a fast-curing, tough, hard finish is desired, such as for kitchen cabinets and office furniture. Comes in two parts - a resin and an acid catalyst. The first is a blend of an amino resin and an alkyd. The acid catalyst is added right before application in a set ratio determined by the manufacturer. Most produce minimal yellowing. There are, however, two downsides to this finish. The first is that as the finish cures, it gives off formaldehyde, which is toxic and carcinogenic. The second is that the finish can crack or craze if too many coats are applied. n a general sense, lacquer is a clear or coloured varnish that dries by solvent evaporation and often a curing process as well that produces a hard, durable finish, in any sheen level from ultra matte to high gloss and that can be further polished as required.

The term lacquer originates from the Portuguese word for lac, a type of resin excreted from certain insects.[1] Regardless, in modern usage, lac-based varnishes are referred to as shellac, while lacquer refers to other polymers dissolved in volatile organic compounds (VOCs), such as nitrocellulose, and later acrylic compounds dissolved in lacquer thinner, a mixture of several solvents typically containing butyl acetate and xylene or toluene. While both lacquer and shellac are traditional finishes, lacquer is more durable than shellac.

Etymology The French word lacre "a kind of sealing wax", from Portuguese lacre, unexplained variant of lacca "resinous substance", from Arabic lakk, from Persian lak, the verb lac meaning "to cover or coat with laqueur".[2] The root of the word is the Sanskrit word laksha ( ) meaning "one hundred thousand", which was used for both the Lac insect (because of their enormous number) and the scarlet resinous secretion it produces that was used as lacquer in ancient India and neighboring areas.[3][4] Lac resin was once imported in sizeable [5][6] quantity into Europe from India along with Eastern woods. The modern Hindi-Urdu word lakh ( , ), meaning "hundred thousand," is also derived from the same Sanskrit root-word.[3] Urushiol-based lacquers According to Encyclopædia Britannica, varnish resin derived from a tree indigenous to China, species Toxicodendron vernicifluum (formerly Rhus vernicifluum), commonly known as the varnish tree. The manufacturing process was introduced [7] into Japan and remained secret for centuries. These lacquers produce very hard, durable finishes that are both beautiful and very resistant to damage by water, acid, alkali or abrasion. The active ingredient of the resin is urushiol, a mixture of various phenols suspended in water, plus a few proteins. Urushiol-based lacquers differ from most others, being slowdrying, water-based, and set by oxidation and polymerization, rather than by evaporation alone. In order for it to set properly it requires humidity and warm temperature. The phenols oxidize and polymerize under the action of an enzyme laccase, yielding a substrate that, upon proper evaporation of its water content, is hard. Lacquer skills became very highly developed in India and Asia, and many highly decorated pieces were produced. The process of lacquer application in India is different from that which is followed in China and Japan. There are two types of lacquer: one obtained from the T. Vernicifluum tree and the other from an insect. In India the insect lac was once used from which a red dye was first extracted, later what was left of the insect was a grease that was used for lacquering objects. The fresh resin from the T. vernicifluum trees causes urushiol-induced contact dermatitis and great care is required in its use. The Chinese treated the allergic reaction with shell-fish. The contemporary theory held that from China, knowledge of lacquer technology was introduced to Korea, and from there to Japan. It was believed that Japan had also been using lacquer from ancient times, but the systematic process of application was developed by the Chinese. With the discovery of lacquer ware in Japan dating back to J mon period, conflicting theories

claim that technology may have been independently developed in Japan. Trade of lacquer objects traveled through various routes to the Middle East. Known applications of lacquer in China included coffins, plates, music instruments and furniture. Lacquer mixed with powdered cinnabar is used to produce the traditional red lacquerware from China. The trees must be at least 10 years old before cutting to bleed the resin. It sets by a process called "aqua-polymerization", absorbing oxygen to set; placing in a humid environment (called "furo" or "muro" in Japanese, meaning "a bath" or "a room") allows it to absorb more oxygen from the evaporation of the water. Lacquer-yielding trees in Thailand, Vietnam, Burma and Taiwan, called Thitsi, are slightly different; they do not contain urushiol, but similar substances called "laccol" or "thitsiol". The end result is similar but softer than the Chinese or Japanese lacquer. Unlike Japanese and Chinese Toxicodendron verniciflua resin, Burmese lacquer does not cause allergic reactions; it sets slower, and is painted by craftsmen's hands without using brushes. Raw lacquer can be "coloured" by the addition of small amounts of iron oxides, giving red or black depending on the oxide. There is some evidence that its use is even older than 8,000 years from archeological digs in China. Later, pigments were added to make colours. It is used not only as a finish, but mixed with ground fired and unfired clays applied to a mould with layers of hemp cloth, it can produce objects without need for another core like wood. The process is called "kanshitsu" in Japan. Advanced decorative techniques using additional materials such as gold and silver powders and flakes ("makie") were refined to very high standards in Japan also after having been introduced from China. In the lacquering of the Chinese musical instrument, the guqin, the lacquer is mixed with deer horn powder (or ceramic powder) to give it more strength so it can stand up to the fingering. There are more than four forms of urushiol which is written as thus: Nitrocellulose lacquers Quick-drying solvent-based lacquers that contain nitrocellulose, a resin obtained from the nitration of cotton and other cellulostic materials, were developed in the early 1920s, and extensively used in the automobile industry for 30 years. Prior to their introduction, mass produced automotive finishes were limited in colour, with Japan Black being the fastest drying and thus most popular. General Motors Oakland automobile brand automobile was the first (1923) to introduce one of the new fast drying nitrocelluous lacquers, a bright blue, produced by DuPont under their Duco tradename. These lacquers are also used on wooden products, furniture primarily, and on musical instruments and other objects. The nitrocellulose and other resins and plasticizers are dissolved in the solvent, and each coat of lacquer dissolves some of the previous coat. These lacquers were a huge improvement over earlier automobile and furniture finishes, both in ease of application, and in colour retention. The preferred method of applying quick-drying lacquers is by spraying, and the development of nitrocellulose lacquers led to the first extensive use of spray guns. Nitrocellulose lacquers produce a very hard yet flexible, durable finish that can be polished to a high sheen. Drawbacks of these lacquers include the hazardous nature of

the solvent, which is flammable, volatile and toxic; and the handling hazards of nitrocellulose in the lacquer manufacturing process. Lacquer grade of soluble nitrocellulose is closely related to the more highly nitrated form which is used to make explosives. They are not toxic after about a month after the lacquer has dissolved all the solvents used to make this kind of lacquer. Acrylic lacquers Lacquers using acrylic resin, a synthetic polymer, were developed in the 1950s. Acrylic resin is colourless, transparent thermoplastic, obtained by the polymerization of derivatives of acrylic acid. Acrylic is also used in enamel paints, which have the advantage of not needing to be buffed to obtain a shine. Enamels, however, are slow drying. The advantage of acrylic lacquer is its exceptionally fast drying time. The use of lacquers in automobile finishes was discontinued when tougher, more durable, weather- and chemical-resistant twocomponent polyurethane coatings were developed. The system usually consists of a primer, colour coat and clear topcoat, commonly known as clear coat finishes. Water-based lacquers Due to health risks and environmental considerations involved in the use of solvent-based lacquers, much work has gone in to the development of water-based lacquers. Such lacquers are considerably less toxic and more environmentally friendly, and in many cases, produce acceptable results. More and more water-based colored lacquers are replacing solvent-based clear and colored lacquers in underhood and interior applications in the automobile and other similar industrial applications. Water based lacquers are used extensively in wood furniture finishing as well.[citation needed] Japanning Just as "China" is a common name for Chinese ceramic, [8] "Japan" is an old name for Japanese Lacquerware (made from the sap of the Lacquer Tree) and its European imitations. As Asian and Indian lacquer work became popular in England, France, the Netherlands, and Spain in the 17th century the Europeans developed imitations that were effectively a different technique of lacquering. The European technique, which is used on furniture and other objects, uses varnishes that have a resin base similar to shellac. The technique, which became known as japanning, involves applying several coats of varnish which are each heat-dried and polished. In the 18th Century this type of lacquering gained a large popular following. Vitreous enamel, usually just called enamel, also porcelain enamel in U.S. English, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C (1380 and 1560 °F). The powder melts, flows, and then hardens to a smooth, durable vitreous coating on metal, and also glass or ceramics, although the use of the term "enamel" is often restricted to work on metal, which is all that this article covers; enamelled glass is also called "painted". The fired enameled ware is a fully laminated composite of glass and metal. The word enamel comes from the High German word smelzan (to smelt) via the Old French esmail.[1] Used as a noun, "an enamel" is a usually small decorative object, coated with enamel coating. Enameling is an old and widely-adopted technology, for most of its history mainly used in jewellery and decorative art, but since the 19th century applied to many industrial uses and in everyday day consumer objects, especially cooking vessels. "Enamelled" and

"enamelling" have a double "l" except in American English where "enameled" and "enameling" is preferred. History The ancient Egyptians applied enamels to pottery and stone objects, and sometimes jewellery, though the last less often than other ancient Middle Eastern cultures. The ancient Greeks, Celts, Russians, and Chinese also used enamel on metal objects.[2] Enamel was also sometimes used to decorate glass vessels during the Roman period, and there is evidence of this as early as the late Republican and early Imperial periods in the Levantine, Egypt, Britain and the Black Sea.[3] Enamel powder could be produced in two ways; either through the powdering of colored glass, or the mixing of colorless glass powder with pigments such as a metallic oxide.[4] Designs were either painted freehand or over the top of outline incisions, and the technique probably originated in metalworking.[3] Once painted, enamelled glass vessels needed to be fired at a temperature high enough to melt the applied powder, but low enough that the fabric of the vessel itself was not melted. Production is thought to have come to a peak in the Claudian period and persisted for some three hundred years,[3] though archaeological evidence for this technique is limited to some forty vessels or vessel fragments.[3] Enamel was at its most important in European art history in the Middle Ages, beginning with the Late Romans and then the Byzantines who began to use cloisonné enamel in imitation of cloisonné inlays of precious stones. This style was widely adopted by the "barbarian" peoples of Migration Period northern Europe. The Byzantines then began to use cloisonné more freely to create images, which was also copied in Western Europe. The champlevé technique was considerably easier, and very widely practiced in the Romanesque period. In Gothic art the finest work is in basse-taille and ronde-bosse techniques, but cheaper champlevé works continued to produced in large numbers for a wider market. From Byzantium or the Islamic world the cloisonné technique reached China in the 13-14th centuries; the first written reference is in a book of 1388, where it is called "Dashi ('Muslim') ware". No Chinese pieces clearly from the 14th century are known, the earliest datable pieces being from the reign of the Xuande Emperor (1425± 35), which however show a full use of Chinese styles suggesting considerable experience in the technique. It remained very popular in China until the 19th century, and is still produced today. The most elaborate and highly-valued Chinese pieces are from the early Ming Dynasty, especially the reigns of the Xuande Emperor and Jingtai Emperor (1450±57), although 19th century or modern pieces are far more common.[5] The Japanese also produced large quantities from the mid-19th century, of very high technical quality.[6] From more recent history, the bright, jewel-like colors have made enamel a favored choice for designers of jewelry and bibelots, such as the fantastic eggs of Peter Carl Fabergé, enameled copper boxes of Battersea enamellers, and artists such as George Stubbs and other painters of portrait miniatures. Enameling was a favorite technique of the Art Nouveau jewelers. Enamel was first applied commercially to sheet iron and steel in Austria and Germany in about 1850. Industrialization increased as the purity of raw materials increased and costs decreased. The wet application process started with the discovery of the use of clay to suspend frit in water. Developments that followed during the twentieth century include enameling-grade steel, cleaned-only surface preparation, automation, and ongoing improvements in efficiency, performance, and quality.[7]

Properties Enamel may be transparent or opaque when fired; vitreous enamel can be applied to most metals. The great majority of modern industrial enamel is applied to steel in which the carbon is controlled to prevent reactions at the firing temperatures. Enamel can also be applied to copper, aluminium,[8] stainless steel,[9] cast iron[10] or hot rolled steel, as well as gold and silver. Vitreous enamel has many excellent properties: it is smooth, hard, chemically resistant, durable, scratch resistant (5-6 on the Mohs scale), long-lasting color fastness, easy-to-clean, and cannot burn. Enamel is glass, not paint, so it does not fade with UV light.[11] Its disadvantages are its tendency to crack or shatter when the substrate is stressed or bent, but modern enamels are chip and impact resistant because of good thickness control and thermal expansions well-match to the metal. Its durability has found it many functional applications: early 20th century and some modern advertising signs, interior oven walls, cooking pots, exterior walls of kitchen appliances, cast iron bathtubs, farm storage silos, and processing equipment such as chemical reactors and pharmaceutical chemical process tanks. Commercial structures such as filling stations, bus stations and even Lustron Houses had walls, ceilings and structural elements made of enameled steel. One of the most widespread use of enamel is in the production of quality chalk-boards and marker-boards (typically called 'blackboards' or 'whiteboards') where the wear and chemical resistance properties of the enamel ensure that 'ghosting' or unerasable marks will not occur from normal use as they will with cheaper polymer boards. Also since standard enamelling steel is magnetically attractive they may also be used as magnet boards. Some new developments in the last ten years include enamel/nonstick hybrid coatings, sol-gel functional top-coats for enamels, enamels with a metallic appearance, and new easy-to-clean technologies.[12] The key ingredient of vitreous enamel is a highly friable form of glass called frit. Frit is typically an alkali borosilicate chemistry with a thermal expansion and glass temperature suitable for coating steel. Raw materials are smelted together between 2100 and 2650 °F (1150 and 1450 °C) into a liquid glass that is directed out of the furnace and thermal shocked with either water or steel rollers into frit.[13] Color in enamel is obtained by the addition of various minerals, often metal oxides cobalt, praseodymium, iron, or neodymium. The last creates delicate shades ranging from pure violet through wine-red and warm gray. Enamel can be either transparent, opaque or opalescent (translucent), which is a variety that gains a milky opacity the longer it is fired. Different enamel colors cannot be mixed to make a new color, in the manner of paint. This produces tiny specks of both colors; although the eye can be tricked by grinding colors together to an extremely fine, flour-like, powder. There are three main types of frit. First, ground coats contain smelted-in transition metal oxides such as cobalt, nickel, copper, manganese, and iron that facilitate adhesion to steel. Second, clear and semi-opaque frits contain little coloring material for producing colors. Finally, titanium white cover coat frits are supersaturated with titanium dioxide which creates a bright white color during firing. After smelting, the frit needs to be processed into one of the three main forms of enamel coating material. First, wet process enamel slip (or slurry) is a high solids loading product of grinding the frit with clay and other viscosity-controlling electrolytes. Second, ready-to-use (RTU) is a cake-mix form of the wet process slurry that is ground dry and can be reconstituted by mixing with water at high shear. Finally, electrostatic powder that can be applied as a powder coating is produced by milling frit with a trace level of proprietary additives.

The frit may also be ground as a powder or into a paste for jewelry or silk-screening application. Techniques of artistic enamelling

can be applied directly over a thin unfired ground coat "base coat" layer that is co-fired with the cover coat in a very efficient twocoat/one-fire process. The frit in the ground coat contains smelted-in cobalt and/or nickel oxide as well as other transition metal oxides to catalyze the enamelsteel bonding reactions. During firing of the enamel at between 760 to 895 °C (1400 and 1640 °F), iron oxide scale first forms on the steel. The molten enamel dissolves the iron oxide and precipitates cobalt and nickel. The iron acts the anode in an electrogalvanic reaction in which the iron is again oxidized, dissolved by the glass, and oxidized again with the available cobalt and nickel limiting the reaction. Finally, the surface becomes roughened with the glass anchored into the holes.[21] Pigment VolumeConcentration (PVC)

y

y

y

y

y

y

y

y

y

y y y

Basse-taille, from the French word meaning "low-cut". The surface of the metal is decorated with a low relief design which can be seen through translucent and transparent enamels. The 14th century Royal Gold Cup is an outstanding example.[14] Champlevé, French for "raised field", where the surface is carved out to form pits in which enamel is fired, leaving the original metal exposed; the Romanesque Stavelot Triptych is an example.[15] Cloisonné, French for "cell", where thin wires are applied to form raised barriers, which contain different areas of (subsequently applied) enamel. Widely practiced in Europe, the Middle East and East Asia.[16] Grisaille, French term meaning "in grey", where a dark, often blue or black background is applied, then a palescent (translucent) enamel is painted on top, building up designs in a monochrome gradient, paler as the thickness of the layer of light color increases. Limoges enamel, made at Limoges, France, the most famous European center of vitreous enamel production. Limoges became famous for champlevé enamels from the 12th century onwards, producing on a large scale, and then from the 15th century retained its lead by switching to painted enamel on flat metal plaques. Painted enamel, a design in enamel is painted onto a smooth metal surface. Grisaille and later Limoges enamel are types of painted enamel.[17] Most traditional painting on glass, and some on ceramics, uses what is technically enamel, but is often described by terms such as "painted in enamels", reserving "painted enamel" and "enamel" as a term for the whole object for works with a metal base.[18] Plique-à-jour, French for "braid letting in daylight" where the enamel is applied in cells, similar to cloisonné, but with no backing, so light can shine through the transparent or translucent enamel. It has a stained-glass like appearance; the Mérode Cup is the only surviving medieval example.[19] Ronde bosse, French for "in the round", also known as "encrusted enamel". A 3D type of enameling where a sculptural form or wire framework is completely or partly enameled, as in the 15th century Holy Thorn Reliquary.[20] Stenciling, where a stencil is placed over the work and the powdered enamel is sifted over the top. The stencil is removed before firing, the enamel staying in a pattern, slightly raised. Sgrafitto, where an unfired layer of enamel is applied over a previously fired layer of enamel of a contrasting color, and then partly removed with a tool to create the design. Serigraph, where a silkscreen is used with 60-70in grade mesh. Counter enameling, not strictly a technique, but a necessary step in many techniques, is to apply enamel to the back of a piece as well - sandwiching the metal - to create less tension on the glass so it does not crack.

When pigments are added to a particular coating that are added based on the PVC. What is PVC you say? It is the pigment volume concentration. The pigment volume concentration is essential in determining the amount of a particular pigment that can be added to the polymer of the coating. The pigment has to have sufficient "wetting" by the polymer to create a protective coating. By wetting I mean, that there must be sufficient polymer, or binder, to completely wet or surround all the pigment particles. There must be enough polymer to completely fill the voids between the pigment particles. How do you calculate the PVC? The following equation is used:

% PVC = 100 * Vpigment / (Vpigment + Vnon-volatile binder) Vpigment = pigment volume Vnon-volatile binder = non-volatile binder volume

The point at which there is just sufficient polymer to wet the pigment particles is known as the critical pigment volume concentration (CPVC). Below the CPVC there is sufficient polymer for pigment wetting and above the CPVC there is not. There are abrupt changes in the coatings properties at the CPVC. Below is a depiction of PVC and property changes that occur at the CPVC.

As you can see by the picture above that both gloss and blistering properties decrease as one reaches the CPVC, while permeability increase above the CPVC. Permeability properties increase because above the CPVC there are voids in the coating filled by air and the coating becomes discontinuous. Some of the properties that can be evaluated above and below the CPVC are blistering, gloss, rusting, permeability, enamel hold out, scrub resistance, tensile strength, and contrast ratio. The filling of pigments in a coating is similar to fillers in composites. In a composite the polymer matrix must be in intimate contact with the fiber reinforcing material. If there is not intimate contact then the fiber acts as a defect. The same theory applies here. If there is not enough polymer to wet the pigment then the pigment becomes the defect and the properties of the coating decrease.

Industrial Enamel Application On sheet steel, a ground coat layer is put on first to create adhesion. The only surface preparation required for modern ground coats is a simply degreasing of the steel with a mildly alkaline solution. White and colored second "cover" coats of enamel are applied over the fired ground coat. For electrostatic enamels, the colored enamel powder

Pigments are what give coatings their beautiful colors. There are a wide variety of colors in coatings today so lets talk about the different types of pigments and how they are used. The main categories for the pigments used in coatings are inorganic, organic, metallic, and pearlescent. When choosing a pigment for a particular coatings some of the factors involved are:

y Make the subject of strength. y Facilitate cleaning. yReport

insulating

properties.

All of these compounds should possess the following qualities:

y y y y y y y y y

Refractive index Hiding efficiency Color pH Bulking value Density Hardness Oil absorption Impermeability (barrier properties)

y Dry up soon after application to the surface. y Layer after drying should be everywhere uniform, hard and shiny (when used matt paint surface should be dull.) y The surface layer must be flexible and have no cracks. y The layer should be stable with respect to atmospheric influences.

The idea behind the pigment is to provide color and protect the substrate. To give color to a coating the pigment must create an opacity in the coating. When a coating is opaque the pigment particles present scatter and/or absorb light sufficiently to prevent it from reaching the substrate. Whether or not the pigment imparts opacity is dependant on two characteristic properties: refractive index and particle size. As you can see by the diagram below if the particles do not have a high refractive index, change the direction the light is traveling, there is insufficient hiding of the substrate. Therefore one can still see the substrate. There is a limit to the number of pigment particles in a coating based on the pigment volume concentration (PVC). This is why it is important to have pigment particles with a high refractive index. Based on the refractive index pigments can be separated into two main categories: hiding and extender pigments. Hiding pigments: These pigments possess refractive index values greater than 1.5. Examples of hiding pigments include titanium dioxide, zinc oxide, lithophone, and antimony oxide. Extender pigments: These pigments possess refractive index values close to 1.5. Examples of extender pigments include calcium carbonate, silicas, alkali and alkaline earth metal silicates, and barytes. As said before particle size also has an effect on the effectiveness of the pigment. As the particle size of a pigment decreases, its opacifying ability increases. As shown figure below, a block of glass is transparent while a stack of thin glass slides of the same overall thickness has opacifying ability. Similarly, a large crystal of titanium dioxide appears colorless, but pigment grade titanium dioxide has good opacifying ability. Compositions for coating, polishing and coating surfaces represent the solution of different substances in appropriate solvents or different drying oils in mixtures with mineral paints. As marked on any subject, they quickly dry out and form a colored or colorless thin layer. These drugs include various paints, varnishes, lacquers, decoenamel, etc. The use of these compounds has the following very important goals:
y Making a clean beautiful view of the subject. y Protect the surface of the object from destructive atmospheric influences.

Lucky are the solutions of various substances, mainly resins in solvents. As the solvents are different fatty-drying oils (linseed, poppy, wood, walnut, etc.), essential oils, turpentine, alcohol, ether, hydrocarbons, etc. If the solvent is volatile, then when applying the solution on any surface it evaporates and the solute remains in the form of a thin film. Samples of these coatings are paints and alcohol tsaponovye. The first is a solution of resins in alcohol, the latter - a solution of celluloid or nitrokletchatki in the appropriate volatile solvent. When using as a solvent drying oils the whole mass of the induced varnish dries, forming a solid cover. Drying of the layer of varnish (oil), which occurs under the influence of atmospheric oxygen and light, causes a profound inner change lacquer sdoya: lacquer film becomes a solid, flexible and loses its stickiness. Also used are mixed paints, which are solvent-drying oil and volatile substances. The main materials required for the production of lacquers, are as follows:
y Natural resin , of which the most common: copal, dammar, shellac, sandarac, rosin, amber, benzoin resin, mastic (sealant), turpentine .

Most of these resins of exotic origin, and sources of their production is gradually decreasing. Recently (1927) have become widely used synthetic resins.
y Artificial resins : Bakelite, an artificial shellac, rubber, coumaric resin. Used as food processing colophony (rosin esters, salts of resin acids), etc. y Coloring tar : «dragon's blood, gamboge, akaroid etc. y drying oils : linseed oil, poppy hemp, sunflower, etc. y Volatile solvents : alcohol wine, wood, turpentine, ether, acetone, carbon disulfide, hlorgidriny, gasoline, etc. y dyes : turmeric, carbon black, aniline, mineral paints and other natural and artificial dyes. y Other chemicals : the various oxides of lead and manganese, lead sugar, smolyanokisly lead and manganese, lead and manganese, lnyanokisly, etc., apply mainly way to increase the drying capacity of varnish.

The most widely used are oil paints, because of the strength and diversity of their properties. Usually they are used when you want to protect subjects from exposure to air, moisture, dust, etc. The best oil varnishes are made from copal, but can be successfully applied and amber. Recently dug replace esters of resin acids, and finally for oil varnishes applied asphalt. It should be noted that the slower drying oil paints, so they are stronger, and their elasticity depends on the amount contained in the varnish of oil: the more oil, so they are more elastic. The quality of paint depends primarily on the type of resin used, as well as the quantity and quality of drying oils. In order to avoid the difficult associated with greater loss of substance and a known fire hazard melting of solid resin (which also would be possible only in the factory setting), is now being successfully applied various direct solvents, such as: acetylene tetrachloride, monochlorobenzene, dichlorobenzene, hlorgidrin, methyl ethyl ketone, acetone, cyclic ketones, etc. In a carbon tetrachloride, most resins are not soluble. The addition of strong wine spirit making them soluble. In addition, carbon tetrachloride, has the property to decrease in the mixture with ether, alcohol, benzene, etc., their combustibility. Experiments revealed that gasoline becomes combustible when mixing one part of it with 9 volume parts chetyrehhlornstogo carbon. A mixture of 6 parts of bulk gasoline with 4 volume parts of carbon tetrachloride is ignited at room temperature when approaching a match and burns very smoky flame. A simpler method of manufacture is the production of paints turpentine, gasoline and ether or alcohol varnish, as in this case for the dissolution of resin or no heating is required, or it requires small amounts. However, varnishes, obtained by this method, there is little resistant to the impact of air and therefore suitable only for objects that are inside buildings, mainly for furniture, metal, leather, paper, etc. They are eye desiccation and give a good thin transparent coating with a shiny surface. When making a good alcoholic varnish usually applied shellac, determine commitment transparent lacquer film.