PATINA

Post 358 – by Gautam Shah

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Patina is a thin crust like surface layer forming on Bronze. Similar surface layers formed on other metals, stone, pottery, wood, etc. are also called Patina. Metal patina is a coating formed due to environmental exposure consisting of oxides, carbonates, sulfides, or sulfates. Patinas are formed by degradation of the surface mass and so etch or reduce its thickness. Some patinas, however, curtail further degradation of the surface and so are encouraged. Patinas are visually appealing and so desired.

Patinated and ormolu Empire timepiece representing Mars and Venus, an allegory of the wedding of Napoleon I and Archduchess Marie Louise of Austria in 1810.

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Metal artefacts exposed to different environments such air, sea-water, soils acquire patina. Similar effects can be achieved by designed exposure and by treating with various chemicals. Patinas are commonly green, but may vary in colour such as of red, brown, black, blue, or gray colours. Its surface may be smooth, glossy, or crusty. Patina also refers to accumulated changes on surface texture and colour, due to long term use of an object like coins or items of wood furniture.

Bronze_head_(Glyptothek_Munich_457)_with_and_without_patina_Bunte_Götter_exhibition

Desert patina or Varnish is a thin, dark red to black mineral coating (of iron and manganese oxides and silica) seen on exposed pebbles and rocks in desert terrains. This is deposition of moisture dissolved minerals drawn to the surface by capillary action of evaporation. Wind abrasion removes the softer salts, and polishes the surface to a glossy finish. In geology and geomorphology, the stone patina also refers to a case-hardened layer, called cortex, or corticated layer on the surface of Flint tools or a chert nodule.

Desert Varnish stones

PATINA has probable origin from a Latin word for shallow dish, or patere’, =to lie open. By extension, the word is applied to the discoloured or in-crusted surface of marble, flint, etc. The chemical process, by which patina forms, is called patination, and an artefact coated by patina is said to be patinated. Newly made objects are deliberately patinated to simulate the antiquity. The process is often called distressing.

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Firearms nominally carry Parkerizing, a bluing finish, (bonderizing, phosphatizing) a conversion coating treatment for corrosion and wear resistance to a steel surface. These objects develop patina after the bluing finish gets worn. Firearms with such patina finish are highly valuable antiques.

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Statue of Liberty NY USA -Patina

Patinas are created over frying-cooking vessels such as Kadhai and Tava (frying pan and Roti baking pan, India), Woks for Chinese preparations, and other metal baking dishes, by seasoning them with oils and salts, when used for the first time. The patina prevents rusting and food sticking to the vessels. To protect the patina, such vessels are scrubbed lightly, and washed gently with cold water.

Chinese Wok

Verdigris is the natural patina formed over copper, brass or bronze, when exposed to the air or seawater, over a period of time. It is usually a basic copper carbonate, but near the sea could be a basic copper chloride. The name verdigris comes from the Middle English vertegrez, from the old French verte grez, an alteration of vert-de-Grèce =green of Greece or vert-de-gris =green of grey.

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Patina over copper alloys, such as bronze, due to the chlorides leads to green, while sulphur compounds are brown. The basic palette for patinas on copper alloys is blue-black due to ammonium sulphide, brown-black with liver of sulphur, blue-green for cupric nitrate, and yellow-brown due to ferric nitrate. For new artefacts accelerated patination carried out by applying chemicals with heat. Colours range from matte sandstone yellow to deep blues, greens, whites, reds and various blacks. Some patina colours are achieved by the mix of pigments and chemicals. The surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats. French sculptor Auguste Rodin used to instruct assistants to urinate over bronzes stored or buried in the yard. A temporary-washable patina is produced on copper by vinegar (acetic acid).

Auguste Rodin Balzac Bust 1892

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In architecture, metals, like copper, bronze, etc. have been used for a very long time, for wall cladding, door panelling, ceiling tiles, and roof covering. Copper provides excellent corrosion resistance. Copper surfaces form tough oxide-sulfate patina coating that protects underlying copper mass and resists further corrosion. Copper corrosion products are less toxic. Copper sheets have been used in many building to cover rounded domes, and articulated roof surfaces. Architectural copper is, though susceptible to oxidizing acids, heavy-metal salts, alkali, sulfur and nitrogen oxides, ammonia, sulfur and ammonium compounds. Brass, an alloy of copper and zinc, has good resistance to atmospheric corrosion, alkali, and organic acids.

Kresge Auditorium MIT

One of the most common surface degradation products is rust on steels Rust is flaky and friable, and it provides no protection to the underlying iron, unlike the formation of patina on copper or bronze surfaces. Rust is permeable to air and water, therefore the interior metallic iron beneath a rust layer continues to corrode. Rust prevention thus requires coatings that preclude rust formation.

Copper Roof Dresden

METALS TREATMENTS for CORROSION RESISTANCE

METALS TREATMENTS for CORROSION RESISTANCE

Post 344 ⇒   by Gautam Shah 

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Corrosion is oxidation of metals in reaction with an oxidant such as oxygen. Rusting is formation of iron oxides through gradual destruction of the material by chemical reaction with the environment. Corrosion or degradations as a process of wearing away of the mass also occurs in ceramics (efflorescence of bricks and terracotta), stones, glass and polymers. Corrosion can be local or more widespread affecting the entire surface. Corrosion is a diffusion process and occurs on the exposed surfaces. One of the main methods of preventing such destruction is to isolate the surface from its environment, including the atmosphere and contact with other passive materials.

Glass disease or corrosion

Acid rain damaged gargoyle

Bishnupur W Bengal, India Corroded Brick work

Both, Ferrous and Non ferrous metals, have a tendency to corrode that is the atom lose electrons and become ions. This is called an anodic reaction, and for the corrosion process to proceed there must be a corresponding cathodic perceptor that adsorbs the electrons.

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Reasons for corrosion could be:

External (environmental)

Internal (constitutional)

Structural (joint system)

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There are several ways prevent, reduce or terminate the corrosion.

Metals get corroded by the environment. In most cases, to create an ideal environment for surrounding the metal will require a very large and extensive system, and possibly large quantity of energy to maintain it.

Corrosion occurs due to the discharge of electrons. Metal electrons migrate due to electrical potential that builds up amongst different metals and between the metal and an electric conductive substance, of an assembly. If cathodic polarity is imposed by supplying an electric DC current to reverse the direction or by attaching sacrificial anodes such as aluminium or magnesium, whose atomic relationship with steel is such that a current is generated without external assistance (the anodes are earthed and have electrolytic continuity with the structure).

Next course is to isolate the metal from corrosion conducive aspects of environment (such as moisture, water, acidic fumes, chlorides etc.). Coatings and plating provide the required isolation. The most appropriate way would be to place the isolating element as close to the metal surface, as possible, and if feasible even integrate it into the metal itself. Electroplating, metalizing etc., are some of the techniques that are on the verge of integration.

Copper roof on the Minneapolis City Hall, coated with patina

Corrosion can also be controlled by constitutionally upgrading the metal, by one of the following techniques.

Mechanical -stress induction and relief techniques at Normal, Hot and Cold temperatures,

  Chemical -additive and subtractive treatments

  Alloying – solid solution, precipitation, amalgamation.

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STUCCO WORK

Post 299 – by Gautam Shah

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Stucco work has been interpreted as architectural plaster work, surface texture rendering, painting technique, ornamentation body and sculpting material. It has been also used as a wet ground for fresco painting and dry gesso surface base for painting. Stucco creates a dull or matt surface, so in recent periods it has been used for Calcimine or Dry Distemper and Oil bound Distemper (OBD)  painting systems.

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Palladio built his projects from bricks plastered with stucco rather then stones clad with marbles like his contemporaries. The ornate capitals for columns were made of terracotta. The pediments and architraves were made of, if wood covered with straw lathing and then stucco. He avoided using, the then popular tapestries, to cover the interior walls and instead applied frescoes.

Style European Art Stucco Rococo Facade Painting

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The varied interpretations across ages and cultures relate to the different techniques, materials and purposes, but all relate to surface rendering system. It is now often used for substantial coating systems that are applied with textural effect, convert into a textured formation, or allow ‘work’ post application. These coating systems are based on polymeric emulsions (or Latex systems, as known in USA).

complex of Sultan Qalawun Cairo

Stucco work has been persistently used for interiors, but more diversely on exterior surfaces. In interiors stucco was a surface forming system over which variety of coatings (such as Fresco, Encaustic, Oil, Acrylic) and mural making (such as glass, ceramics, inlay) techniques were applied. On exterior face it was used as a surface rendering (texture) system like for sculpting decorative motifs, figurines and statuettes, and for formation of applique architectonic elements (such as pilasters, tympanums, pendants, pediments, cornices, column fluting, pillars’ heads and bases).

Iran Stucco

Stucco-work began as a wall coating system, probably to rejuvenate the soot-covered walls (blackened due to oil lamp lighting and indoor fires’). It provided a smooth surface over a variety of wall surfaces such as adobe, reeds, brick and stone. Examples of stucco-work occur in the Aztec architecture of Mexico, Egypt, Sumerian buildings and Greek buildings. Romans erected masonry structures, often with recovered materials from ruins of earlier age buildings. These walls were of random pattern, and required plaster as well as textural renderings. For faster finishing of vast buildings, stucco was ideal system for interior and exterior work. With little craftsmanship it provided ‘sculpted and decorative’ artefacts for middle class to replace marble and other stones.

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Stucco work reached new heights during Baroque period. Renaissance period provided smoother stucco surfaces in buildings to contrast the rusticated stone’s corners of openings. Post Renaissance period saw festoons and medallions of stucco on exterior walls. During Gothic period stucco work applied to wood a lath lattice was used for creating intricate ceiling patterns. Walls had cornices, freezes and panels over wood base. It was also realized that a plain wood wall was darker in colour and was susceptible to fire on the other hand stucco or gypsum-covered walls could be painted by water-based coatings (lime-wash, calcimine, distemper, etc.) and, these were fire resistant.

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The basic ingredient for stucco work has been Lime, with addition of Gypsum and marble dust. Other reinforcing additives were hair, fibres, stone chips, etc. Gypsum was costly material, yet it was used with marble dust for imitation marble finishes called Scagliola. Since industrial revolution Portland Cement is being added, and in last 50 years polymeric binders are included.

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Stucco and Plaster work have overlapping interpretations. Plaster is comparatively planer work, created from Gypsum, Lime or Portland Cement and applied for surface leveling and waterproofing. Stucco can have the same materials but applied for creating designs, patterns and statuettes, on internal and external surfaces. The base surface could be structural elements like slabs, walls, and framed or latticed work. Stucco were once created from slow setting lime or gypsum but nowadays could have chemical and polymer binders. High bodied paint formulations applied with texturing tools are also used.

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SURFACE PREPARATIONS

Post 196 – by Gautam Shah

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Rif;ing firearms refers to helical groovings into the barrel of a gun for the purpose of exerting torque and imparting a spin to a projectile

Natural and Industrially-produced materials require some degree of surface preparations or treatments before being put to functional use or for readying it for the next process. The next processes could be surface application like coating, cladding, mounting, plating, joining, welding, levelling, cleaning, washing, ph balancing, static removal, etc. Surface preparation could involve processes that induce new surface qualities such as textures, ionization, etc.

Card_scraper_-_making_violinThe surface preparation at simplest level could be checking and assuring, mainly through visual observation and touch-feel that no foreign materials have remained on the surface, and all loose (removable) materials are detached. These simple processes ensure integrity of the surface.

Record Player Music Record Vinyl Turntable Needle

Surface preparation is required for material objects with their own natural or process-formed surfaces. It is also necessary for further processing of material objects and application of surface finish systems.

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Surface preparations are physical, chemical and mechanical processes.

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  • Physical processes are used to remove unwanted particles or materials (such as rust, nodules, residual deposits, dust or grease, lubricants, cutting-oils, etc.) adhering to the surface. Rubbing, air-dusting, vacuum cleaning, wiping, water-bathing, etc. remove such adhered materials. The particles have remained on the surface due to the holding by surface texture, bonding or ion attraction, and horizontal storage. Washing with soap or a surface active agent (surfactant) can weaken the ion attraction break the weak molecular bond generate by-products that can be removed easily.

Hot-dip galvanizing on a steel handrail.

  • Chemical processes include acid-alkali treatments and solvent washing. The processes roughen, etch or smoothen the surface. In many instances the resultant by-product is beneficial or neutral, so allowed to remain on the surface. In other instances a secondary treatment is required just to remove the by-products of the first treatment. Sometimes Surface preparation agents themselves are the primary surface finishes. Such agents cover the surface area as an intermediary film. Such films help in bonding of the final surface finish. Chemical processes also include burnishing, flame-treatments, surface annealing and hardening, cathodic modification, sputtering and material’s depositions.

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  • Mechanical Processes affect the surface superficially. Cleaning the surface by removal processes include abrading, grinding, rubbing, blasting, planning, chipping, etc. There are several surface preparation processes that instead of removing materials, only alter the surface with newer textures by engraving, patterning, surface deformation, etc.

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  • New application of surfaces is made to level or create textured surfaces. Some such processes are integral to art-painting methods. The levelling plasters are made with plastic soils (such as used in pottery), and various qualities of lime or chalk materials. In many instances the powdered mineral and colourants are `loaded’ on a freshly coated `wet’ surface. Colours are also blown as dry powders or applied as pastes and dabbed (pressed) into the wet plaster. Such wet coloured plaster surfaces are then engraved or embossed with textures to facilitate the penetration of colours. Similar techniques are used to produce a bass or relief effects, or provide a highlighting boundary to the drawn object.

Major and Knapp Engraving Co. Park Place, N.Y. Abstract medium print lithograph, tinted

  • Gesso, a mixture of plaster of Paris (or gypsum) with size, is the traditional ground. The first layer is of gesso grosso, a mixture of coarse, un-slaked plaster and size. This provides a rough, absorbent surface for ten or more thin coats of gesso sotile, a smooth mixture of size and fine plaster previously slaked in water to retard drying. This labourious preparation results, however, in an opaque, brilliant white, light-reflecting surface, similar in texture to hard, flat icing sugar.

 

 

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GLOSS

Post 190 –by Gautam Shah

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SURFACE GLOSS

Objects are seen when illuminated. Light illuminates objects, but in the process affects it in several ways. Some light is absorbed within it which is mainly responsible for perception of colour. If the object is transparent to translucent, than part of the light gets transmitted though it. The transmitted light (through the object) may get re-reflected through the object. In the process the re-reflected light gets scattered. Light also gets specularly reflected from it the surface of the object provided it has reflective properties.

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Nearly reflective surface -Glossy coating on wood https://www.flickr.com/photos/editor/2065638637/sizes/z/

Specular reflection: The substantial quantum of light is reflected from the surface, in equal and opposite direction, to the angle of incident light.

Diffuse reflection: The light that gets scattered in many directions.

Vietnam Veterans Memorial, National Mall

lathe turned pillars chennakeshava_temple_in_belur

Gloss is one of the most important of parameters that describe the visual appearance of an object. It is an optical property of a surface to reflect light in a specular (mirror-like) direction. A specular reflection can be said to be a reflection in very small range of direction. This is distinctively different from diffuse reflection, where the incoming light is reflected in a broad range of directions. Factors that determine the gloss are the refractive index of the material, the angle of incident light and the surface topography.

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early american room

Distinctive examples of specular and diffuse reflections are glossy and matte paints. Matte paints have almost exclusively diffuse reflection, while glossy paints have both specular and diffuse reflections’. A surface of a non-absorbing material such as plaster, are nearly perfect diffuser, whereas polished metallic objects, glass, and some polymers are specularly reflective.

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Texture of a surface is a key determinant of level of specular reflection. Objects with a smooth surface, i.e. highly polished or containing coatings with finely dispersed pigments, appear shiny to the eye due to a large amount of light being reflected in a specular direction. Rough surfaces have irregular defects or undulations which scatter the light in other directions, and so appear dull. Dull surfaces do not reflect the image (like a mirror), so the reflections seem blurred and distorted.

 

airport-hall-wait-window

In case of transparent and translucent materials, not only there is surface level specular reflection but the back face coatings-treatments and closely placed materials (substrate materials) also reflect specularly. The reflecting material of mirrors is the highly polished surface of glass, and its capacity to reflect light from the back side coating of lead, aluminium or silver.

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Gloss is often considered a subjective term (though scientific tests exist) for representing specular reflection of a surface. Commercially, in the surface finish world, gloss is recognized as Flat or matte, Egg shell, Semi-gloss, Full gloss. A Flat surface is considered free from sheen even when viewed at an oblique angle whereas at the other extreme Full gloss is a mirror like face at all angles of view. Satin (silk) finish is somewhere between Egg shell and semi gloss finish.

A rough guide for level of gloss of a surface is: Flat (0 to 10 % reflective), Low Sheen (10 to 25% reflective), whereas Glossy (70–90% reflective).

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Dull-matt surface

Dull- matt surface Unglazed Ceramic

  • The non-reflecting surface of a flat-matt finish helps to hide or de-emphasize the imperfections of the surface to be painted. Semi-gloss finish and high-gloss finishes highlight such imperfections. Flat-matt surfaces do not reflect light at any angle so are very useful as a coating-finishing over very extensive surfaces such as corridors, lobbies, halls, ceilings, and exterior faces, etc. Flat-matt finishes over the floors, also offer an assurance of their being no slippery surface. Flat-matt surfaces show off true colours at all angles, so are visually more recognizable. Flat-matt surfaces may look patchy if the substrate or the application techniques are improper. Automobile interior trims are intentionally designed to be of matt finish so as to minimize the irritating reflection while driving.

Reflective-Glossy Roof

Walt Disney Concert Hall LA CA

Walt Disney Concert Hall LA CA

  •  Semi-gloss and full gloss finishes offer better wearing, cleaning and humidity resistance than flat paints. Flat paints may show polishing or burnishing marks when rubbed for cleaning. Semi gloss surfaces are slightly deceptive and may not show true colour or depth perception.
Brushed Matt metal finish

Brushed Matt metal finish

  •  High gloss surfaces get easily tarnished by oil, grease or waxy streaks. High gloss surfaces are first to show off substrate impurities and malfunctioning of plasticizing agents or entrapped moisture, etc. High gloss surfaces show of minute scratches or dents etc. in terms of defective specular reflection. High gloss surfaces are very deceptive in colour recognition.

Glasses

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LACQUERS or NC LACQUERS

Postby Gautam Shah

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Lacquer is a very generic term applied to a variety of coating systems. It indicates a surfacing system, where a film forming substance has been dissolved in or diluted with a solvent. On application the solvent evaporates leaving a thin film on the surface.

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Lac or Shellac is a type of resin, produced by insects thriving on the cell sap of certain host plants. It is produced in Eastern parts of India and the SE Asia. The natural resin, as extracted contains internal and external impurities. These are removed mechanically, by melting and filtration processes. Two main forms are commercially available, Button and prills or flakes. Other custom products include coloured sticks for colouring and moulding craft items.
Wax is a natural constituent of Lac forming 2.5 to 5%. Lac Wax was often used, in Floor-polishes and cosmetics, later replaced by Carnauba wax. Lac Dyes were used for silk and wool, than Lac as a resin, in early 19th C before the availability of Synthetic Dyes.

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Lac or shellac is bio-degradable, eco-friendly, tasteless and non-toxic material. So ideal for children toys, play-cards, book cover coatings, etc. It is highly inflammable, softens with and so can be moulded. Moulded lacquer is used for making bangles and jewellery embellishments. The moulding process involves heating, combining with additives, colours, kneading, hammering and shaping into a mass like dough.

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The lacquer, on evaporation of its solvents changes the phase from Liquid to Solid, but does not convert itself into different substance. Lacquer films are soluble in the (original) solvent. Lacquers are also thermoplastic (will soften with an increase in heat) materials. The film forming substances of lacquers are linear polymers high in polymer weight with good solvent releasing property. Such substances are often very hard and brittle, so require addition of plasticizers to achieve better adhesion, flexibility and durability of the gloss.

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Commercially the term Lacquer is applied to Solvent-based Coating systems (against water-based systems) that offer hard, glossy and durable film. In this sense, there are Two basic varieties:

1 Thermoplastics type: Nitro cellulose, Acrylics, Chlorinated Rubber, Vinyls, Epoxy.

2 Thermosetting type: Acrylics, Epoxy Resins, Polyurethanes, Vinyls, Alkyd, Melamine.

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Cellulosic Polymers

Cellulose is the most widely occurring, a natural polymer, available in almost all plants. Primary sources of industrial cellulose are cotton fibres and wood. Cellulose is a polyhydric-alcohol, and forms esters with organic acids. It also forms reaction products with inorganic acids. These cellulosic derivatives used in production of various types of lacquers are classified as:

1. esters of inorganic acids -nitro cellulose

2. esters of organic acids -cellulose acetate

3. others -methyl and ethyl cellulose

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Lacquers can be classified into two basic groups:

NC Lacquers and Acrylic or Plastic Lacquers.

Lamellar Lines Mudguard Horizontal Lacquered Sheet

Nitro Cellulose Lacquers

NC Lacquers consist of Nitro cellulose as the main raw material to which a variety of plasticizer and resins are added, to provide wide range of film properties. PLASTICIZERS increase elasticity and extensibility of the film. Commonly used Plasticizers are, blown-castor oil, dibutyl phthalate, dioctyl phthalate, dibutyl sebacate, butyl stearate, chlorinated diphenyls. Additions of RESINS increase gloss and adhesion of the film. The resins are coconut and castor oil alkyds, maleic modified ester gum, cyclohexanone (ketonic) resins, acrylic resins, toluene sulfonamides formaldehyde resins.

Lacquered_secretaire,_Residenzmuseum,_2017-09-13

NC Lacquers are produced by dissolving or diluting lacquer and suitable plasticizers in a mix of solvents. The SOLVENTS act in three ways: Active solvents are (ethyl acetate, butyl acetate), Latent solvents (ethyl alcohol, butyl alcohol, diacetone alcohol), and Diluents (toluene, xylene). A suitable mix of these basic three types of solvents is known as `Thinner‘. A very specific quality of Thinner is required for each application and weather condition.

NC Lacquers do not become yellow with ageing. It has no peeling problem. Lacquers provide very ‘water-white’ (no colouration or tinge) film. NC Lacquers are re-coatable and removable substances.

NC Lacquers are used on wood, metals, metals like gold, silver and copper, plastics, leather, paper, fabrics, as hair-fixers, and Nail-polishes. Lacquer is one of the best surface sealing material for wood products and so forms the primer coat for melamine, etc. 

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Solvent-based nitrocellulose lacquers (from resin of nitration of cotton (lint) and other cellulose based materials, were used commercially from the 19th C. These lacquers began to replace shellac lacquer and were used as protective or rust inhibitive clear coatings for brass musical instruments, gift items and furniture. These were also used in white-goods products (refrigerators, irons, cooking tops, etc. and in automobiles. These lasted for several decades till arrival of ‘Polymer based lacquers‘.

These materials are called Lacquers because the film is ‘water-white’. Acrylic lacquers of thermoplastic type are characterized by a transparent water white film, very good resistance to decolouration from temperature and UV light, good electrical properties, outdoor durability, excellent resistance to mineral oil-greases, resistance to chemical fumes, resistance to water based alkaline substances.

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Acrylic lacquers convertible coating that is on drying covert to a different product, which is non-dissoluble and non-removable. These are used for: wood items, clear coating for brass, copper, and aluminium, as a top coat for final gloss and protection air-crafts, automobiles, toys, auto-parts, industrial components, consumer durables, TV cabinets. These are used as clear-invisible coating for exposed surfaces like bricks, stones and concrete. Acrylic lacquers with soluble dyes form transparent glass coatings. One of the major uses is for internal coatings of food and beverage cans.

Thermosetting Acrylics provide a hard and scratch proof coating, good colour retention, better water and detergent resistance, better gloss and chalking resistance.

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VARNISH

Post –by Gautam Shah

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Varnish is clear coating of resin and solvent that dries-hardens to transparent film. Today, Varnish is a generic term for Clear Coatings that provide a colourless (transparent) and (mostly) a glossy surface.

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Clear Coatings are required for several reasons, such as to show-up the surface grain, colour, pattern, or protect artwork or craft pieces. The surface to be coated may not always be perfect or decent. So some form of Conditioning of the substrate surfaces is needed before application of a clear coating.

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The most common problems with surfaces are like:

    1. uneven colour
    2. unsuitable tone
    3.          uneven grain or pattern
    4.          patchy absorbency
    5.          uneven texture
    6.          bleeding or soluble constituents
    7.          waxy or oily deposits
    8.          alkalinity
    9.          acidity
    10.      .   galvanic sensitivity
    11.          moisture content and transfer

Varnished Wood Chair

The word ‘varnish’ comes from Latin ‘vernix’, meaning an odorous resin, Varnish as word comes from Greek ‘Berenice’, which was the ancient name of modern Benghazi in Libya. Perhaps the first varnishes were produced from resins of local trees of Benghazi.

Wooden Decking Paint Wood House Deck Varnish

Varnishes are clear coatings usually made with oils, oleo-resinous substances and alkyds. Varnishes are comparatively slow drying, high bodied finishes and so can be applied by brush, unlike Lacquer or French polish. Varnish types of finishes have thicker film of high gloss, with better wear and tear resistance.

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Varnishes are convertible coatings (materials, which after application change into different but permanent substance), so are more stable.

In the past varnishes were made by boiling linseed or tung oil with modified rosins. Later varnishes were produced from oils with maleic or phenolic modified resins. Nowadays air drying varnishes (oxidation & polymerization) are produced from long oil alkyds, where as baking varnishes (heat polymerization) are produced from medium or short oil alkyds. Often amino resins such as urea and melamine formaldehyde are added to produce a very tough, hard wearing, solvent insoluble, alkali resistant, non yellowing and non degrading film.

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Magic Letters Deck

High temperature baking varnishes though superior in many respects have limited use so far as wood, paper and such other surfaces are concerned. Theoretically any film forming medium (used for manufacturing paints -coloured coatings) can be used as a clear coating material, but certain film peculiarities and clarity restrict their use. High grade clear coatings could be of polyurethane, epoxy, polyester, PVA, materials. Varnishes besides wood, are used on paper, leather, fabrics, copper winding wires, pottery products, polymers, insides of food tin and aluminium cans, glass, electronic circuit boards, toys etc.

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