1.
Printmaking
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Printmaking is the process of making artworks by printing, normally on paper. Printmaking normally covers only the process of creating prints that have an element of originality, except in the case of monotyping, the process is capable of producing multiples of the same piece, which is called a print. Each print produced is not considered a copy but rather is considered an original, a print may be known as an impression. Printmaking is not chosen only for its ability to multiple impressions. Prints are created by transferring ink from a matrix or through a screen to a sheet of paper or other material. Screens made of silk or synthetic fabrics are used for the screenprinting process, other types of matrix substrates and related processes are discussed below. Multiple impressions printed from the matrix form an edition. Prints may also be printed in book form, such as illustrated books or artists books, Printmaking techniques are generally divided into the following basic categories, Relief, where ink is applied to the original surface of the matrix. Relief techniques include woodcut or woodblock as the Asian forms are known, wood engraving. Intaglio, where ink is applied beneath the surface of the matrix. Intaglio techniques include engraving, etching, mezzotint, aquatint, planographic, where the matrix retains its original surface, but is specially prepared and/or inked to allow for the transfer of the image. Planographic techniques include lithography, monotyping, and digital techniques, stencil, where ink or paint is pressed through a prepared screen, including screenprinting and pochoir. Other types of printmaking techniques outside these groups include collagraphy and viscosity printing, collagraphy is a printmaking technique in which textured material is adhered to the printing matrix. This texture is transferred to the paper during the printing process, Contemporary printmaking may include digital printing, photographic mediums, or a combination of digital, photographic, and traditional processes. Many of these techniques can also be combined, especially within the same family, for example, Rembrandts prints are usually referred to as etchings for convenience, but very often include work in engraving and drypoint as well, and sometimes have no etching at all. Woodcut, a type of print, is the earliest printmaking technique. It was probably first developed as a means of printing patterns on cloth, woodcuts of images on paper developed around 1400 in Japan, and slightly later in Europe. These are the two areas where woodcut has been most extensively used purely as a process for making images without text, the artist draws a design on a plank of wood, or on paper which is transferred to the wood
2.
Etching
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Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio in the metal. In modern manufacturing, other chemicals may be used on other types of material, as a method of printmaking, it is, along with engraving, the most important technique for old master prints, and remains in wide use today. In a number of variants such as microfabrication etching and photochemical milling it is a crucial technique in much modern technology. In traditional pure etching, a plate is covered with a waxy ground which is resistant to acid. The artist then scratches off the ground with an etching needle where he or she wants a line to appear in the finished piece. The échoppe, a tool with an oval section, is also used for swelling lines. The plate is dipped in a bath of acid, technically called the mordant or etchant. The acid bites into the metal where it is exposed, leaving behind lines sunk into the plate, the remaining ground is then cleaned off the plate. The plate is inked all over, and then the ink wiped off the surface, the plate is then put through a high-pressure printing press together with a sheet of paper. The paper picks up the ink from the lines, making a print. The process can be repeated many times, typically several hundred impressions could be printed before the shows much sign of wear. The work on the plate can also be added to by repeating the whole process, Etching has often been combined with other intaglio techniques such as engraving or aquatint. The process as applied to printmaking is believed to have been invented by Daniel Hopfer of Augsburg, Hopfer was a craftsman who decorated armour in this way, and applied the method to printmaking, using iron plates. Apart from his prints, there are two examples of his work on armour, a shield from 1536 now in the Real Armeria of Madrid. The switch to copper plates was made in Italy. On the other hand, the handling of the ground and acid need skill and experience, prior to 1100 AD, the New World Hohokam independently utilized the technique of acid etching in marine shell designs. Jacques Callot from Nancy in Lorraine made important technical advances in etching technique and he developed the échoppe, a type of etching-needle with a slanting oval section at the end, which enabled etchers to create a swelling line, as engravers were able to do. Callot also appears to have responsible for an improved, harder, recipe for the etching ground
3.
Engraving
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Engraving is the practice of incising a design onto a hard, usually flat surface by cutting grooves into it. Wood engraving is a form of printing and is not covered in this article. Engraving was an important method of producing images on paper in artistic printmaking, in mapmaking. Other terms often used for printed engravings are copper engraving, copper-plate engraving or line engraving, hand engraving is a term sometimes used for engraving objects other than printing plates, to inscribe or decorate jewellery, firearms, trophies, knives and other fine metal goods. Traditional engravings in printmaking are also engraved, using just the same techniques to make the lines in the plate. Each graver is different and has its own use, engravers use a hardened steel tool called a burin, or graver, to cut the design into the surface, most traditionally a copper plate. Modern professional engravers can engrave with a resolution of up to 40 lines per mm in high grade work creating game scenes, dies used in mass production of molded parts are sometimes hand engraved to add special touches or certain information such as part numbers. In addition to engraving, there are engraving machines that require less human finesse and are not directly controlled by hand. They are usually used for lettering, using a pantographic system, there are versions for the insides of rings and also the outsides of larger pieces. Such machines are used for inscriptions on rings, lockets. Gravers come in a variety of shapes and sizes that yield different line types, the burin produces a unique and recognizable quality of line that is characterized by its steady, deliberate appearance and clean edges. The angle tint tool has a curved tip that is commonly used in printmaking. Florentine liners are flat-bottomed tools with multiple lines incised into them, ring gravers are made with particular shapes that are used by jewelry engravers in order to cut inscriptions inside rings. Flat gravers are used for work on letters, as well as wriggle cuts on most musical instrument engraving work, remove background. Knife gravers are for line engraving and very deep cuts, round gravers, and flat gravers with a radius, are commonly used on silver to create bright cuts, as well as other hard-to-cut metals such as nickel and steel. Square or V-point gravers are typically square or elongated diamond-shaped and used for cutting straight lines, V-point can be anywhere from 60 to 130 degrees, depending on purpose and effect. These gravers have very small cutting points, other tools such as mezzotint rockers, roulets and burnishers are used for texturing effects. Burnishing tools can also be used for stone setting techniques
4.
Aquatint
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Aquatint is an intaglio printmaking technique, a variant of etching. In intaglio printmaking, the artist makes marks on the plate that are capable of holding ink, the inked plate is passed through a printing press together with a sheet of paper, resulting in a transfer of the ink to the paper. This can be repeated a number of times, depending on the particular technique, like etching, aquatint uses the application of a mordant to etch into the metal plate. Where the engraving uses a needle to make lines that print in black. The rosin is acid resistant and typically adhered to the plate by controlled heating, the tonal variation is controlled by the level of mordant exposure over large areas, and thus the image is shaped by large sections at a time. Another tonal technique, mezzotint, begins with a surface that is evenly indented so that it will carry a fairly dark tone of ink. The mezzotint plate is then smoothed and polished to make areas carry less ink, alternatively, beginning with a smooth plate, areas are roughened to make them darker. Occasionally these two techniques are combined, the painter and printmaker Jan van de Velde IV invented the aquatint technique in Amsterdam, around 1650. The cartographer Peter Perez Burdett later introduced his secret aquatint technique to England in the 1770s, an aquatint requires a metal plate, an acid, and something to resist the acid. Traditionally copper or zinc plates were used, the artist applies a ground that will resist acid. Ground is applied by either dissolving powdered resin in spirits, applying the powder directly to the surface of the plate, in all forms of etching the acid resist is commonly referred to as the ground. An aquatint box is used to apply resin powder, the powder is at the bottom of the box, a crank or a bellows is used to blow the powder up into the air of the box. A window allows the engraver to see the density of flowing powder, when the powder covers the plate, it can be extracted from the box for the next operations. The plate is then heated, if the plate is covered with powder, the resin melts forming a fine and even coat, if it is in spirits, the spirits evaporate and the result is essentially the same. Now the plate is dipped in acid, producing an even, at this point, the plate is said to carry about a 50% halftone. This means that, were the plate printed with no further biting, at some point the artist will then etch an outline of any aspects of the drawing s/he wishes to establish with line, this provides the basis and guide for the later tone work. S/he may also have applied an acid-resistant stop out if s/he intends to keep any areas totally white and free of ink, the artist then begins immersing the plate in the acid bath, progressively stopping out any areas that have achieved the designed tonality. These tones, combined with the limited line elements, give aquatints a distinctive, also, aquatints, like mezzotints, provide ease in creating large areas of tone without laborious cross-hatching, but aquatint plates, it is noted, are generally more durable than mezzotint plates
5.
Lithography
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Lithography is a method of printing originally based on the immiscibility of oil and water. The printing is from a stone or a plate with a smooth surface. It was invented in 1796 by German author and actor Alois Senefelder as a method of publishing theatrical works. Lithography can be used to print text or artwork onto paper or other suitable material, Lithography originally used an image drawn with oil, fat, or wax onto the surface of a smooth, level lithographic limestone plate. The stone was treated with a mixture of acid and gum arabic, when the stone was subsequently moistened, these etched areas retained water, an oil-based ink could then be applied and would be repelled by the water, sticking only to the original drawing. The ink would finally be transferred to a paper sheet. This traditional technique is used in some fine art printmaking applications. In modern lithography, the image is made of a coating applied to a flexible aluminum plate. The image can be printed directly from the plate, or it can be offset, by transferring the image onto a sheet for printing. In fact, photolithography is used synonymously with offset printing, the technique as well as the term were introduced in Europe in the 1850s. Beginning in the 1960s, photolithography has played an important role in the fabrication, Lithography uses simple chemical processes to create an image. For instance, the part of an image is a water-repelling substance. Thus, when the plate is introduced to a printing ink and water mixture, the ink will adhere to the positive image. This allows a flat print plate to be used, enabling much longer, Lithography was invented by Alois Senefelder in the Kingdom of Bavaria in 1796. In the early days of lithography, a piece of limestone was used. After the oil-based image was put on the surface, a solution of gum arabic in water was applied, during printing, water adhered to the gum arabic surfaces and was repelled by the oily parts, while the oily ink used for printing did the opposite. Lithography works because of the repulsion of oil and water. The image is drawn on the surface of the print plate with a fat or oil-based medium such as a wax crayon, which may be pigmented to make the drawing visible
6.
M. C. Escher
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Maurits Cornelis Escher, or commonly M. C. Escher, was a Dutch graphic artist who made mathematically inspired woodcuts, lithographs, early in his career, he drew inspiration from nature, making studies of insects, landscapes, and plants such as lichens, all of which he used as details in his artworks. Apart from being used in a variety of papers, his work has appeared on the covers of many books. He was one of the inspirations of Douglas Hofstadters 1979 book Gödel, Escher. Maurits Cornelis Escher was born on 17 June 1898 in Leeuwarden, Friesland and he was the youngest son of the civil engineer George Arnold Escher and his second wife, Sara Gleichman. In 1903, the moved to Arnhem, where he attended primary and secondary school until 1918. Known to his friends and family as Mauk, he was a sickly child, although he excelled at drawing, his grades were generally poor. He also took carpentry and piano lessons until he was thirteen years old, in 1918, he went to the Technical College of Delft. From 1919 to 1922, Escher attended the Haarlem School of Architecture and Decorative Arts, learning drawing and he briefly studied architecture, but he failed a number of subjects and switched to decorative arts, studying under the graphic artist Samuel Jessurun de Mesquita. In 1922, an important year of his life, Escher traveled through Italy, visiting Florence, San Gimignano, Volterra, Siena, in the same year he traveled through Spain, visiting Madrid, Toledo, and Granada. He was impressed by the Italian countryside, and in Granada by the Moorish architecture of the fourteenth-century Alhambra, Escher returned to Italy, and lived in Rome from 1923 to 1935. While in Italy, Escher met Jetta Umiker – a Swiss woman, the couple settled in Rome where their first son, Giorgio Arnaldo Escher, named after his grandfather, was born. Escher and Jetta later had two sons, Arthur and Jan. He travelled frequently, visiting Viterbo in 1926, the Abruzzi in 1927 and 1929, Corsica in 1928 and 1933, Calabria in 1930, the townscapes and landscapes of these places feature prominently in his artworks. In May and June 1936, Escher travelled back to Spain, revisiting the Alhambra, the sketches he made in the Alhambra formed a major source for his work from that time on. He also studied the architecture of the Mezquita, the Moorish mosque of Cordoba and this turned out to be the last of his long study journeys, after 1937, his artworks were created in his studio rather than in the field. All the same, even his work already shows his interest in the nature of space, the unusual, perspective. In 1935, the climate in Italy became unacceptable to Escher
7.
Prince Rupert of the Rhine
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Rupert was a younger son of the German prince Frederick V, Elector Palatine and his wife Elizabeth, the eldest daughter of James I of England. Thus Rupert was the nephew of King Charles I of England, who made him Duke of Cumberland and Earl of Holderness, and his sister Electress Sophia was the mother of George I of Great Britain. Prince Rupert had a varied career and he was a soldier from a young age, fighting against Spain in the Netherlands during the Eighty Years War, and against the Holy Roman Emperor in Germany during the Thirty Years War. Aged 23, he was appointed commander of the Royalist cavalry during the English Civil War, becoming the archetypal Cavalier of the war and he surrendered after the fall of Bristol and was banished from England. He served under Louis XIV of France against Spain, and then as a Royalist privateer in the Caribbean, Rupert died in England in 1682, aged 62. Rupert is considered to have been a quick-thinking and energetic cavalry general, in the Interregnum, Rupert continued the conflict against Parliament by sea from the Mediterranean to the Caribbean, showing considerable persistence in the face of adversity. As the head of the Royal Navy in his years, he showed greater maturity and made impressive and long-lasting contributions to the Royal Navys doctrine. As a colonial governor, Rupert shaped the geography of modern Canada—Ruperts Land was named in his honour. He also played a role in the early African slave trade, Ruperts varied and numerous scientific and administrative interests combined with his considerable artistic skills made him one of the more colourful individuals of the Restoration period. Rupert was born in Prague in 1619, at the start of the Thirty Years War, to Frederick V, Elector Palatine, and Elizabeth Stuart and he was given his name in honour of King Rupert of Germany, a famous Wittelsbach ancestor. Ruperts father was a member of the Holy Roman Empire. This support was not forthcoming, resulting in a defeat at the hands of his Catholic enemies at the Battle of White Mountain in 1620. Ruperts parents were mockingly termed the Winter King and Queen as a consequence of their reigns in Bohemia having lasted only a single season. Rupert was almost left behind in the rush to escape Ferdinands advance on Prague, until Kryštof z Donína. Rupert accompanied his parents to The Hague, where he spent his years at the Hof te Wassenaer. Ruperts mother paid her children little attention even by the standards of the day, apparently preferring her pet monkeys, the result was a strict school routine including logic, mathematics, writing, drawing, singing and playing instruments. As a child, Rupert was at times badly behaved, fiery, mischievous, nonetheless, Rupert proved to be an able student. By the age of three he could speak some English, Czech and French, and mastered German while still young and he excelled in art, being taught by Gerard van Honthorst, and found the maths and sciences easy
8.
English Civil War
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The English Civil War was a series of armed conflicts and political machinations between Parliamentarians and Royalists over, principally, the manner of Englands government. The war ended with the Parliamentarian victory at the Battle of Worcester on 3 September 1651, the monopoly of the Church of England on Christian worship in England ended with the victors consolidating the established Protestant Ascendancy in Ireland. The term English Civil War appears most often in the singular form, the war in all these countries are known as the Wars of the Three Kingdoms. Unlike other civil wars in England, which focused on who should rule, this war was more concerned with the manner in which the kingdoms of England, Scotland, the two sides had their geographical strongholds, such that minority elements were silenced or fled. The strongholds of the royalty included the countryside, the shires, on the other hand, all the cathedral cities sided with Parliament. All the industrial centers, the ports, and the advanced regions of southern and eastern England typically were parliamentary strongholds. Lacey Baldwin Smith says, the words populist, rich, at times there would be two groups of three lines allowing one group to reload while the other group arranged themselves and fired. Mixed in among the musketeers were pikemen carrying pikes that were between 12 feet and 18 feet long, whose purpose was to protect the musketeers from cavalry charges. The Royalist cavaliers skill and speed on horseback led to early victories. While the Parliamentarian cavalry were slower than the cavaliers, they were better disciplined. The Royalists had a tendency to chase down individual targets after the initial charge leaving their forces scattered and tired, Cromwells cavalry, on the other hand, trained to operate as a single unit, which led to many decisive victories. The English Civil War broke out fewer than forty years after the death of Queen Elizabeth I in 1603, in spite of this, James personal extravagance meant he was perennially short of money and had to resort to extra-Parliamentary sources of income. Charles hoped to unite the kingdoms of England, Scotland and Ireland into a new single kingdom, many English Parliamentarians had suspicions regarding such a move because they feared that setting up a new kingdom might destroy the old English traditions which had bound the English monarchy. As Charles shared his fathers position on the power of the crown, at the time, the Parliament of England did not have a large permanent role in the English system of government. Instead, Parliament functioned as an advisory committee and was summoned only if. Once summoned, a continued existence was at the kings pleasure. Yet in spite of this role, Parliament had, over the preceding centuries. Without question, for a monarch, Parliaments most indispensable power was its ability to tax revenues far in excess of all other sources of revenue at the Crowns disposal
9.
Peter Lely
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Sir Peter Lely was a painter of Dutch origin, whose career was nearly all spent in England, where he became the dominant portrait painter to the court. Lely was born Pieter van der Faes to Dutch parents in Soest in Westphalia, Lely studied painting in Haarlem, where he may have been apprenticed to Pieter de Grebber. He became a master of the Guild of Saint Luke in Haarlem in 1637 and he is reputed to have adopted the surname Lely from a heraldic lily on the gable of the house where his father was born in The Hague. He arrived in London in around 1641, which was marked by the death of Anthony van Dyck in December and his early English paintings, mainly mythological or religious scenes, or portraits set in a pastoral landscape, show influences from Anthony van Dyck and the Dutch baroque. Lelys portraits were well received, and he succeeded Anthony van Dyck as the most fashionable portrait artist in England and he became a freeman of the Painter-Stainers Company in 1647 and was portrait artist to Charles I. His talent ensured that his career was not interrupted by Charless execution, and he served Oliver Cromwell, whom he painted warts and all, in the years around 1650 the poet Sir Richard Lovelace wrote two poems about Lely – Peinture and See what a clouded majesty. After the English Restoration in 1660, Lely was appointed as Charles IIs Principal Painter in Ordinary in 1661, with a stipend of £200 per year, Lely became a naturalised English subject in 1662. The young Robert Hooke came to London to follow an apprenticeship with Lely before being given a place at Westminster School by Richard Busby, demand was high, and Lely and his large workshop were prolific. After Lely painted a head, Lelys pupils would often complete the portrait in one of a series of numbered poses. As a result, Lely is the first English painter who has left a mass of work. On Lely’s death in 1680 his executors employed a dozen such slaves to complete for sale the many unfinished canvases stacked about his studio and his most famous non-portrait work is probably Nymphs by a fountain in Dulwich Picture Gallery. Lely played a significant role in introducing the mezzotint to Britain and he encouraged Dutch mezzotinters to come to Britain to copy his work, laying the foundations for the English mezzotint tradition. He died soon afterwards at his easel in Covent Garden, while painting a portrait of the Duchess of Somerset, and was buried at St Pauls Church, Covent Garden. Some items in it which had acquired by Lely from the Commonwealth dispersal of Charles Is art collections. He was replaced as court portraitist by Sir Godfrey Kneller, also a German-born Dutchman, whose style drew from Lelys, between them they established the basic English portrait style followed by less fashionable painters for decades. Amongst Lelys pupils were John Greenhill and Willem Wissing, a horse was also named after him, finishing fourth in the 1996 Grand National. Peter Lelys works Millar, Oliver Lely, Sir Peter Grove Dictionary of Art,19, pp. 119–125 Millar, Oliver Sir Peter Lely 1618-80, National Portrait Gallery,1978. Painting in Britain 1530 to 1790, fourth Edition, New York, Viking Penguin,1978
10.
Royal Academy Summer Exhibition
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The Summer Exhibition is an open art exhibition held annually by the Royal Academy in Burlington House, Piccadilly in central London, England, during the summer months of June, July, and August. The exhibition includes paintings, prints, drawings, sculpture, architectural designs and models, when the Royal Academy was founded in 1768 one of its key objectives was to establish an annual exhibition, open to all artists of merit, which could be visited by the public. The first Summer Exhibition took place in 1769, it has held every year since without exception. Today, around 1,000 works are selected each year from as many as 10,000 entries representing some 5,000 artists, any artist may submit up to two works at a fee of £25 per piece for selection by The Summer Exhibition Selection and Hanging Committee. Due to the significant increase in the volume of entries over recent years, the number of entries per artist was reduced to 2, the committee is formed from the Council of Academicians and is traditionally chaired by the President of the Royal Academy. In addition to those selected by the committee, all 80 Academicians are entitled to have six of their own pieces in the exhibition. The 2005 exhibition theme was Printmaking and the multiple, in 2006, the theme was From Life. In 2008, the theme was Man Made, the theme for 2010 was Raw. In 2011, the committee agreed to have no specific theme. For the 2006 exhibition, the received a statue and a plinth from David Hensel. By mistake, the two parts were judged independently, with the result that the statue was rejected and the put on display. The RA Summer Exhibition usually opens to the public in early June, the main event is called Varnishing Day, the day that, according to popular legend, artists would come to add a final coat of varnish to their paintings. Traditionally, artists walk in procession from Burlington House to St Jamess Church, Piccadilly, at the opening reception the shortlists for various prizes are announced. Over £70,000 prize money, including the £25,000 Charles Wollaston Award, is awarded each year at the Summer Exhibition, in addition, a £10.000 architectural prize is awarded. Almost all exhibited works are for sale, the Academy receives 30% of the purchase price, in 2003, this amounted to a sum of some £2,000,000 for the institution, which receives no financial support from the state or crown. The Royal Academy revisited, Victorian paintings from the Forbes magazine Collection, new York, The Metropolitan Museum of Art
11.
Metal
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A metal is a material that is typically hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable—that is, they can be hammered or pressed permanently out of shape without breaking or cracking—as well as fusible and ductile, about 91 of the 118 elements in the periodic table are metals, the others are nonmetals or metalloids. Some elements appear in both metallic and non-metallic forms, astrophysicists use the term metal to collectively describe all elements other than hydrogen and helium, the simplest two, in a star. The star fuses smaller atoms, mostly hydrogen and helium, to larger ones over its lifetime. In that sense, the metallicity of an object is the proportion of its matter made up of all chemical elements. Many elements and compounds that are not normally classified as metals become metallic under high pressures, the atoms of metallic substances are typically arranged in one of three common crystal structures, namely body-centered cubic, face-centered cubic, and hexagonal close-packed. In bcc, each atom is positioned at the center of a cube of eight others, in fcc and hcp, each atom is surrounded by twelve others, but the stacking of the layers differs. Some metals adopt different structures depending on the temperature, atoms of metals readily lose their outer shell electrons, resulting in a free flowing cloud of electrons within their otherwise solid arrangement. This provides the ability of metallic substances to easily transmit heat, while this flow of electrons occurs, the solid characteristic of the metal is produced by electrostatic interactions between each atom and the electron cloud. This type of bond is called a metallic bond, Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over various timescales. Examples,4 Na + O2 →2 Na2O2 Ca + O2 →2 CaO4 Al +3 O2 →2 Al2O3, the transition metals are slower to oxidize because they form a passivating layer of oxide that protects the interior. Others, like palladium, platinum and gold, do not react with the atmosphere at all, some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades. The oxides of metals are generally basic, as opposed to those of nonmetals, exceptions are largely oxides with very high oxidation states such as CrO3, Mn2O7, and OsO4, which have strictly acidic reactions. Painting, anodizing or plating metals are good ways to prevent their corrosion, however, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two form an electrochemical cell, and if the coating is less reactive than the coatee. Metals in general have high conductivity, high thermal conductivity. Typically they are malleable and ductile, deforming under stress without cleaving, in terms of optical properties, metals are shiny and lustrous. Sheets of metal beyond a few micrometres in thickness appear opaque, although most metals have higher densities than most nonmetals, there is wide variation in their densities, lithium being the least dense solid element and osmium the densest
12.
Copper
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Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of copper has a reddish-orange color. Copper is one of the few metals that occur in nature in directly usable metallic form as opposed to needing extraction from an ore and this led to very early human use, from c.8000 BC. Copper used in buildings, usually for roofing, oxidizes to form a green verdigris, Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as agents, fungicides, and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the hemoglobin in fish. In humans, copper is found mainly in the liver, muscle, the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. The filled d-shells in these elements contribute little to interatomic interactions, unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper, at the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form. The softness of copper partly explains its high conductivity and high thermal conductivity. The maximum permissible current density of copper in open air is approximately 3. 1×106 A/m2 of cross-sectional area, Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air, as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. A green layer of verdigris can often be seen on old structures, such as the roofing of many older buildings. Copper tarnishes when exposed to sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper, 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper, both have a spin of 3⁄2
Robinson, Gerald Philip (1911). . In Chisholm, Hugh. Encyclopædia Britannica. 18 (11th ed.). Cambridge University Press. pp. 351–353. This includes a detailed description of mezzotint history and methods.
Robinson, Gerald Philip (1911).