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138-405: Although the history of terrazzo can be traced back to the ancient mosaics of Egypt, its more recent predecessors come from Italy. The form of terrazzo used today derives partly from the 18th century pavimento alla Veneziana ( Venetian pavement) and the cheaper seminato. Pavimento alla Veneziana had workers place marble fragments next to each other in a mortar base. Terrazzo is also related to

276-459: A catalyst . Laboratory synthesis of biopolymers, especially of proteins , is an area of intensive research. There are three main classes of biopolymers: polysaccharides , polypeptides , and polynucleotides . In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase . The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from

414-442: A galera . Due to its likelihood of cracking, terrazzo was used at a small scale in comparison to the large expanses we see today. Two inventions resulted in its rise in popularity: divider strips and the electric grinding machine. The invention of divider strips by L. Del Turco and Bros. in 1924 contained the cracking of terrazzo by allowing the material greater space to expand and shrink after installation. This invention made terrazzo

552-441: A lower critical solution temperature phase transition (LCST), at which phase separation occurs with heating. In dilute solutions, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces between the solvent and monomer subunits dominate over intramolecular interactions. In

690-454: A 1 inch (25 mm) layer of sandy concrete. Before this layer sets, terrazzo workers partially embed metal divider strips in the concrete wherever there is to be a joint or change of color in the terrazzo. For the final layer, terrazzo workers blend and place into each of the panels a fine marble chip mixture that may be color-pigmented. While the mixture is still wet, workers toss additional marble chips of various colors into each panel and roll

828-502: A bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. In the theta solvent , or the state of the polymer solution where the value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition), the polymer behaves like an ideal random coil . The transition between

966-480: A crab, a lobster, shrimps, mushrooms, flowers, a stag and two cruciform designs surround the smaller of the two inscriptions, which reads: In fulfilment of the vow (prayer) of those whose names God knows. This anonymous dedicatory inscription is a public demonstration of the benefactors' humility and an acknowledgement of God's omniscience. The abundant variety of natural life depicted in the Butrint mosaics celebrates

1104-562: A deer, four young men wrestling a wild bull to the ground, and a gladiator resting in a state of fatigue, staring at his slain opponent. The mosaics decorated the walls of a cold plunge pool in a bath house within a Roman villa. The gladiator mosaic is noted by scholars as one of the finest examples of mosaic art ever seen – a "masterpiece comparable in quality with the Alexander Mosaic in Pompeii ." A specific genre of Roman mosaic

1242-408: A degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For many polymers, crystallinity may also be associated with decreased transparency. The space occupied by a polymer molecule is generally expressed in terms of radius of gyration , which

1380-587: A deviation from a simple linear chain. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include star polymers , comb polymers , polymer brushes , dendronized polymers , ladder polymers , and dendrimers . There exist also two-dimensional polymers (2DP) which are composed of topologically planar repeat units. A polymer's architecture affects many of its physical properties including solution viscosity, melt viscosity, solubility in various solvents, glass-transition temperature and

1518-405: A durable and reliable material in addition to allowing for further design work within the floor. Installers use the dividing strips as guides when they work with different colored terrazzo. Additionally, the electric grinding machine and mechanization of the production process cut down on costs and installation time, making terrazzo an affordable flooring option. Art Deco and Moderne styles from

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1656-403: A flexible membrane can be installed so that cracks do not appear on the surface. Unbonded includes the sand cushion method which uses wire reinforcing, an isolation sheet, and sand dusting that absorbs any movement from the concrete slab. Although terrazzo derives from the mosaic artform, it does not necessarily place individual pieces in a decorative pattern. Instead, small pieces are thrown into

1794-464: A flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible. The attractive forces between polymer chains play a large part in determining the polymer's properties. Because polymer chains are so long, they have many such interchain interactions per molecule, amplifying the effect of these interactions on the polymer properties in comparison to attractions between conventional molecules. Different side groups on

1932-479: A given application, the properties of a polymer can be tuned or enhanced by combination with other materials, as in composites . Their application allows to save energy (lighter cars and planes, thermally insulated buildings), protect food and drinking water (packaging), save land and lower use of fertilizers (synthetic fibres), preserve other materials (coatings), protect and save lives (hygiene, medical applications). A representative, non-exhaustive list of applications

2070-416: A golden background date back to the 5th and to the 8th century, although it was restored many times later. The baptistery of the basilica, which was demolished in the 15th century, had a vault covered with gold-leaf tesserae, large quantities of which were found when the site was excavated. In the small shrine of San Vittore in ciel d'oro, now a chapel of Sant'Ambrogio, every surface is covered with mosaics from

2208-557: A high input of energy. Gourdin and Kingery (1975) estimate that the production of any given amount of lime requires about five times that amount of wood. Recent experiments by Affonso and Pernicka have shown that only twice the amount is needed, but that would still amount to 4.5 metric tonnes of dry wood for the floors in Çayönü. Other sites with terrazzo floors include Nevalı Çori, Göbekli Tepe , Jericho , and Kastros ( Cyprus ). Terrazzo artisans create walls, floors, patios , and panels by exposing marble chips and other fine aggregates on

2346-402: A high surface quality and are also highly transparent so that the laser properties are dominated by the laser dye used to dope the polymer matrix. These type of lasers, that also belong to the class of organic lasers , are known to yield very narrow linewidths which is useful for spectroscopy and analytical applications. An important optical parameter in the polymer used in laser applications

2484-609: A major form of artistic expression. The Roman church of Santa Costanza , which served as a mausoleum for one or more of the Imperial family, has both religious mosaic and decorative secular ceiling mosaics on a round vault, which probably represent the style of contemporary palace decoration. The mosaics of the Villa Romana del Casale near Piazza Armerina in Sicily are the largest collection of late Roman mosaics in situ in

2622-533: A more intimate and delicate style, of which The Angel before St Joachim — with its pastoral backdrop, harmonious gestures and pensive lyricism – is considered a superb example. The 9th- and 10th-century mosaics of the Hagia Sophia in Constantinople are truly classical Byzantine artworks. The north and south tympana beneath the dome was decorated with figures of prophets, saints and patriarchs. Above

2760-401: A polymer behaves as a continuous macroscopic material. They are classified as bulk properties, or intensive properties according to thermodynamics . The bulk properties of a polymer are those most often of end-use interest. These are the properties that dictate how the polymer actually behaves on a macroscopic scale. The tensile strength of a material quantifies how much elongating stress

2898-421: A polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. A polymer which contains only a single type of repeat unit is known as a homopolymer , while a polymer containing two or more types of repeat units is known as a copolymer . A terpolymer is a copolymer which contains three types of repeat units. Polystyrene

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3036-433: A polymeric material can be described at different length scales, from the sub-nm length scale up to the macroscopic one. There is in fact a hierarchy of structures, in which each stage provides the foundations for the next one. The starting point for the description of the structure of a polymer is the identity of its constituent monomers. Next, the microstructure essentially describes the arrangement of these monomers within

3174-536: A process called reptation in which each chain molecule is constrained by entanglements with neighboring chains to move within a virtual tube. The theory of reptation can explain polymer molecule dynamics and viscoelasticity . Depending on their chemical structures, polymers may be either semi-crystalline or amorphous. Semi-crystalline polymers can undergo crystallization and melting transitions , whereas amorphous polymers do not. In polymers, crystallization and melting do not suggest solid-liquid phase transitions, as in

3312-427: A result, they typically have lower melting temperatures than other polymers. When a polymer is dispersed or dissolved in a liquid, such as in commercial products like paints and glues, the chemical properties and molecular interactions influence how the solution flows and can even lead to self-assembly of the polymer into complex structures. When a polymer is applied as a coating, the chemical properties will influence

3450-529: A similar iconography. 6th-century pieces are rare in Rome but the mosaics inside the triumphal arch of the basilica of San Lorenzo fuori le mura belong to this era. The Chapel of Ss. Primo e Feliciano in Santo Stefano Rotondo has very interesting and rare mosaics from the 7th century. This chapel was built by Pope Theodore I as a family burial place. In the 7th–9th centuries Rome fell under

3588-456: A statistical distribution of chain lengths, the molecular weight is expressed in terms of weighted averages. The number-average molecular weight ( M n ) and weight-average molecular weight ( M w ) are most commonly reported. The ratio of these two values ( M w / M n ) is the dispersity ( Đ ), which is commonly used to express the width of the molecular weight distribution. The physical properties of polymer strongly depend on

3726-845: A surface. Mosaics are often used as floor and wall decoration, and were particularly popular in the Ancient Roman world. Mosaic today includes not just murals and pavements, but also artwork, hobby crafts, and industrial and construction forms. Mosaics have a long history, starting in Mesopotamia in the 3rd millennium BC. Pebble mosaics were made in Tiryns in Mycenean Greece; mosaics with patterns and pictures became widespread in classical times, both in Ancient Greece and Ancient Rome . Early Christian basilicas from

3864-487: A temple building in Abra, Mesopotamia , and are dated to the second half of 3rd millennium BC. They consist of pieces of colored stones, shells and ivory. Excavations at Susa and Chogha Zanbil show evidence of the first glazed tiles, dating from around 1500 BC. However, mosaic patterns were not used until the times of Sassanid Empire and Roman influence. Bronze Age pebble mosaics have been found at Tiryns ; mosaics of

4002-537: A tendency to form amorphous and semicrystalline structures rather than crystals . Polymers are studied in the fields of polymer science (which includes polymer chemistry and polymer physics ), biophysics and materials science and engineering . Historically, products arising from the linkage of repeating units by covalent chemical bonds have been the primary focus of polymer science. An emerging important area now focuses on supramolecular polymers formed by non-covalent links. Polyisoprene of latex rubber

4140-432: A variety of different but structurally related monomer residues; for example, polynucleotides such as DNA are composed of four types of nucleotide subunits. A polymer containing ionizable subunits (e.g., pendant carboxylic groups ) is known as a polyelectrolyte or ionomer , when the fraction of ionizable units is large or small respectively. The microstructure of a polymer (sometimes called configuration) relates to

4278-636: A weighted roller (100–125 pounds (45–57 kg)) over the entire surface. In the 1970s, polymer -based terrazzo was introduced and is called thin-set terrazzo. Initially polyester and vinyl ester resins were used as the binder resin. Today, most of the terrazzo installed is epoxy terrazzo. The advantages of this material over cementitious terrazzo include a wider selection of colors, 1 ⁄ 4 to 3 ⁄ 8 inch (6.4 to 9.5 mm) installation thickness, lighter weight, faster installation, impermeable finish, higher strength, and less susceptibility to cracking. The disadvantage of epoxy resin–based terrazzo

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4416-405: A wide-meshed cross-linking between the "main chains". Close-meshed crosslinking, on the other hand, leads to thermosets . Cross-links and branches are shown as red dots in the figures. Highly branched polymers are amorphous and the molecules in the solid interact randomly. An important microstructural feature of a polymer is its architecture and shape, which relates to the way branch points lead to

4554-814: Is a substance or material that consists of very large molecules, or macromolecules , that are constituted by many repeating subunits derived from one or more species of monomers . Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers . Their consequently large molecular mass , relative to small molecule compounds , produces unique physical properties including toughness , high elasticity , viscoelasticity , and

4692-479: Is a crucial physical parameter for polymer manufacturing, processing, and use. Below T g , molecular motions are frozen and polymers are brittle and glassy. Above T g , molecular motions are activated and polymers are rubbery and viscous. The glass-transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition of plasticizers . Whereas crystallization and melting are first-order phase transitions ,

4830-410: Is a long-chain n -alkane. There are also branched macromolecules with a main chain and side chains, in the case of polyethylene the side chains would be alkyl groups . In particular unbranched macromolecules can be in the solid state semi-crystalline, crystalline chain sections highlighted red in the figure below. While branched and unbranched polymers are usually thermoplastics, many elastomers have

4968-546: Is a panel in Hagia Sophia depicting Emperor John II and Empress Eirene with the Theotokos (1122–34). The empress with her long braided hair and rosy cheeks is especially capturing. It must be a lifelike portrayal because Eirene was really a redhead as her original Hungarian name, Piroska shows. The adjacent portrait of Emperor Alexios I Komnenos on a pier (from 1122) is similarly personal. The imperial mausoleum of

5106-400: Is also commonly present in polymer backbones, such as those of polyethylene glycol , polysaccharides (in glycosidic bonds ), and DNA (in phosphodiester bonds ). Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. This happens in

5244-512: Is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of pervaded volume , which is the volume spanned by the polymer chain and scales with the cube of the radius of gyration. The simplest theoretical models for polymers in the molten, amorphous state are ideal chains . Polymer properties depend of their structure and they are divided into classes according to their physical bases. Many physical and chemical properties describe how

5382-537: Is an example for conscious archaization as contemporary Byzantine rulers were bearded. A mosaic panel on the gallery shows Christ with Constantine Monomachos and Empress Zoe (1042–1055). The emperor gives a bulging money sack to Christ as a donation for the church. The dome of the Hagia Sophia Church in Thessaloniki is decorated with an Ascension mosaic (c. 885). The composition resembles

5520-481: Is an example of a natural polymer, and the polystyrene of styrofoam is an example of a synthetic polymer. In biological contexts, essentially all biological macromolecules —i.e., proteins (polyamides), nucleic acids (polynucleotides), and polysaccharides —are purely polymeric, or are composed in large part of polymeric components. The term "polymer" derives from Greek πολύς (polus)  'many, much' and μέρος (meros)  'part'. The term

5658-428: Is composed only of styrene -based repeat units, and is classified as a homopolymer. Polyethylene terephthalate , even though produced from two different monomers ( ethylene glycol and terephthalic acid ), is usually regarded as a homopolymer because only one type of repeat unit is formed. Ethylene-vinyl acetate contains more than one variety of repeat unit and is a copolymer. Some biological polymers are composed of

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5796-409: Is defined, for small strains , as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature. Viscoelasticity describes a complex time-dependent elastic response, which will exhibit hysteresis in the stress-strain curve when

5934-839: Is obvious in the apse mosaic of San Michele in Affricisco , executed in 545–547 (largely destroyed; the remains in Berlin ). The last example of Byzantine mosaics in Ravenna was commissioned by bishop Reparatus between 673 and 679 in the Basilica of Sant'Apollinare in Classe. The mosaic panel in the apse showing the bishop with Emperor Constantine IV is obviously an imitation of the Justinian panel in San Vitale. The mosaic pavement of

6072-518: Is partially preserved. The so-called Tomb of the Julii , near the crypt beneath St Peter's Basilica , is a 4th-century vaulted tomb with wall and ceiling mosaics that are given Christian interpretations. The Rotunda of Galerius in Thessaloniki , converted into a Christian church during the course of the 4th century, was embellished with very high artistic quality mosaics. Only fragments survive of

6210-435: Is probably the most famous Byzantine mosaic in Constantinople. The Pammakaristos Monastery was restored by Michael Glabas , an imperial official, in the late 13th century. Only the mosaic decoration of the small burial chapel ( parekklesion ) of Glabas survived. This domed chapel was built by his widow, Martha around 1304–08. In the miniature dome the traditional Pantokrator can be seen with twelve prophets beneath. Unusually

6348-494: Is that it can only be used for interior, not exterior, applications. Epoxy-based terrazzo will lose its color and slightly peel when used outdoors, whereas cement-based terrazzo will not. In addition to marble aggregate blends, other aggregates have been used, such as mother of pearl and abalone shell. Recycled aggregates include: glass, porcelain, concrete, and metal. Shapes and medallions can be fabricated on site by bending divider strips, or off site by water-jet cutting . When

6486-435: Is the change in refractive index with temperature also known as dn/dT. For the polymers mentioned here the (dn/dT) ~ −1.4 × 10 in units of K in the 297 ≤ T ≤ 337 K range. Most conventional polymers such as polyethylene are electrical insulators , but the development of polymers containing π-conjugated bonds has led to a wealth of polymer-based semiconductors , such as polythiophenes . This has led to many applications in

6624-563: Is the main constituent of wood and paper. Hemoglycin (previously termed hemolithin ) is a space polymer that is the first polymer of amino acids found in meteorites . The list of synthetic polymers , roughly in order of worldwide demand, includes polyethylene , polypropylene , polystyrene , polyvinyl chloride , synthetic rubber , phenol formaldehyde resin (or Bakelite ), neoprene , nylon , polyacrylonitrile , PVB , silicone , and many more. More than 330 million tons of these polymers are made every year (2015). Most commonly,

6762-600: The Basilica of San Lorenzo , mosaics executed in the late 4th and early 5th centuries depict Christ with the Apostles and the Abduction of Elijah ; these mosaics are outstanding for their bright colors, naturalism and adherence to the classical canons of order and proportion. The surviving apse mosaic of the Basilica of Sant'Ambrogio , which shows Christ enthroned between Saint Gervasius and Saint Protasius and angels before

6900-842: The Byzantine Empire from the 6th to the 15th centuries. The majority of Byzantine mosaics were destroyed without trace during wars and conquests, but the surviving remains still form a fine collection. The great buildings of Emperor Justinian like the Hagia Sophia in Constantinople , the Nea Church in Jerusalem and the rebuilt Church of the Nativity in Bethlehem were certainly embellished with mosaics but none of these survived. Important fragments survived from

7038-686: The Iconoclastic destruction of the 8th century. Among the rare examples are the 6th-century Christ in majesty (or Ezekiel's Vision ) mosaic in the apse of the Church of Hosios David in Thessaloniki that was hidden behind mortar during those dangerous times. Nine mosaic panels in the Hagios Demetrios Church , which were made between 634 and 730, also escaped destruction. Unusually almost all represent Saint Demetrius of Thessaloniki , often with suppliants before him. This iconoclasm

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7176-603: The Komnenos dynasty, the Pantokrator Monastery was certainly decorated with great mosaics but these were later destroyed. The lack of Komnenian mosaics outside the capital is even more apparent. There is only a "Communion of the Apostles" in the apse of the cathedral of Serres . A striking technical innovation of the Komnenian period was the production of very precious, miniature mosaic icons. In these icons

7314-445: The 12th century. The sack of Constantinople in 1204 caused the decline of mosaic art for the next five decades. After the reconquest of the city by Michael VIII Palaiologos in 1261 the Hagia Sophia was restored and a beautiful new Deesis was made on the south gallery. This huge mosaic panel with figures two and a half times lifesize is really overwhelming due to its grand scale and superlative craftsmanship. The Hagia Sophia Deesis

7452-493: The 1920s to 1940s favored terrazzo with the dividers allowing for straight or curved lines that increased the decorative potential. The popularity of terrazzo led to an increase in installers in the 1920s. The National Terrazzo and Mosaic Organization was formed in 1931 to further professionalize the practice of terrazzo installation. One of the best-known examples of terrazzo is the Hollywood Walk of Fame . Created in 1958,

7590-610: The 4th century BC are found in the Macedonian palace-city of Aegae , and the 4th-century BC mosaic of The Beauty of Durrës discovered in Durrës , Albania in 1916, is an early figural example; the Greek figural style was mostly formed in the 3rd century BC. Mythological subjects, or scenes of hunting or other pursuits of the wealthy, were popular as the centrepieces of a larger geometric design, with strongly emphasized borders. Pliny

7728-577: The 4th century onwards were decorated with wall and ceiling mosaics. Mosaic art flourished in the Byzantine Empire from the 6th to the 15th centuries; that tradition was adopted by the Norman Kingdom of Sicily in the 12th century, by the eastern-influenced Republic of Venice , and among the Rus . Mosaic fell out of fashion in the Renaissance , though artists like Raphael continued to practice

7866-445: The 4th century, still exist. The winemaking putti in the ambulatory of Santa Constanza still follow the classical tradition in that they represent the feast of Bacchus , which symbolizes transformation or change, and are thus appropriate for a mausoleum, the original function of this building. In another great Constantinian basilica, the Church of the Nativity in Bethlehem the original mosaic floor with typical Roman geometric motifs

8004-514: The 5th-century Ravenna , the capital of the Western Roman Empire , became the center of late Roman mosaic art. The Mausoleum of Galla Placidia was decorated with mosaics of high artistic quality in 425–430. The vaults of the small, cross-shaped structure are clad with mosaics on blue background. The central motif above the crossing is a golden cross in the middle of the starry sky. Another great building established by Galla Placidia

8142-530: The Anastasis above the doors, while in the church the Theotokos (apse), Pentecost, scenes from Christ's life and ermit St Loukas (all executed before 1048). The scenes are treated with a minimum of detail and the panels are dominated with the gold setting. The Nea Moni Monastery on Chios was established by Constantine Monomachos in 1043–1056. The exceptional mosaic decoration of the dome showing probably

8280-564: The Apostles. The surviving remains are somewhat fragmented. Massilia remained a thriving port and a Christian spiritual center in Southern Gaul where favourable societal and economic conditions ensured the survival of mosaic art in the 5th and 6th centuries. The large baptistery, once the grandest building of its kind in Western Europe, had a geometric floor mosaic which is only known from 19th century descriptions. Other parts of

8418-545: The DNA to RNA and subsequently translate that information to synthesize the specified protein from amino acids . The protein may be modified further following translation in order to provide appropriate structure and functioning. There are other biopolymers such as rubber , suberin , melanin , and lignin . Naturally occurring polymers such as cotton , starch , and rubber were familiar materials for years before synthetic polymers such as polyethene and perspex appeared on

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8556-577: The Dormition in Nicaea . The crosses were substituted with the image of the Theotokos in both churches after the victory of the Iconodules (787–797 and in 8th–9th centuries respectively, the Dormition church was totally destroyed in 1922). A similar Theotokos image flanked by two archangels were made for the Hagia Sophia in Constantinople in 867. The dedication inscription says: "The images which

8694-513: The Elder mentions the artist Sosus of Pergamon by name, describing his mosaics of the food left on a floor after a feast and of a group of doves drinking from a bowl. Both of these themes were widely copied. Greek figural mosaics could have been copied or adapted paintings, a far more prestigious artform, and the style was enthusiastically adopted by the Romans so that large floor mosaics enriched

8832-695: The Great's Hunt and the Four Seasons . In 1913 the Zliten mosaic , a Roman mosaic famous for its many scenes from gladiatorial contests, hunting and everyday life, was discovered in the Libyan town of Zliten . In 2000 archaeologists working in Leptis Magna , Libya , uncovered a 30 ft length of five colorful mosaics created during the 1st or 2nd century AD. The mosaics show a warrior in combat with

8970-617: The Islamic world after the 8th century, except for geometrical patterns in techniques such as zellij , which remain popular in many areas. Modern mosaics are made by artists and craftspeople around the world. Many materials other than traditional stone, ceramic tesserae, enameled and stained glass may be employed, including shells, beads, charms, chains, gears, coins, and pieces of costume jewelry. Traditional mosaics are made of small cubes of roughly square pieces of stone or hand made glass enamel of different colours, known as tesserae . Some of

9108-612: The Vrina Plain basilica of Butrint , Albania appear to pre-date that of the Baptistery by almost a generation, dating to the last quarter of the 5th or the first years of the 6th century. The mosaic displays a variety of motifs including sea-creatures, birds, terrestrial beasts, fruits, flowers, trees and abstracts – designed to depict a terrestrial paradise of God's creation. Superimposed on this scheme are two large tablets, tabulae ansatae, carrying inscriptions. A variety of fish,

9246-441: The adhesion of the coating and how it interacts with external materials, such as superhydrophobic polymer coatings leading to water resistance. Overall the chemical properties of a polymer are important elements for designing new polymeric material products. Polymers such as PMMA and HEMA:MMA are used as matrices in the gain medium of solid-state dye lasers , also known as solid-state dye-doped polymer lasers. These polymers have

9384-521: The aggregates are often marble dust which is calcium carbonate , strong acid can also cause deterioration to the aggregates. When partial replacement is necessary, a "bracketing" system mixing and matching different chips is used to create potential matches. Aged terrazzo can be resurfaced to restore its original look by re-polishing. Mosaic A mosaic is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster / mortar , and covering

9522-442: The apse is decorated with a Deesis , probably due to the funerary function of the chapel. Polymer A polymer is a substance composed of macromolecules. A macromolecule is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. A polymer ( / ˈ p ɒ l ɪ m ər / )

9660-434: The backbone in a variety of ways. A copolymer containing a controlled arrangement of monomers is called a sequence-controlled polymer . Alternating, periodic and block copolymers are simple examples of sequence-controlled polymers . Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types of tacticity: isotactic (all substituents on

9798-530: The basilica of Santa Maria Maggiore . The 27 surviving panels of the nave are the most important mosaic cycle in Rome of this period. Two other important 5th century mosaics are lost but we know them from 17th-century drawings. In the apse mosaic of Sant'Agata dei Goti (462–472, destroyed in 1589) Christ was seated on a globe with the twelve Apostles flanking him, six on either side. At Sant'Andrea in Catabarbara (468–483, destroyed in 1686) Christ appeared in

9936-421: The case of water or other molecular fluids. Instead, crystallization and melting refer to the phase transitions between two solid states ( i.e. , semi-crystalline and amorphous). Crystallization occurs above the glass-transition temperature ( T g ) and below the melting temperature ( T m ). All polymers (amorphous or semi-crystalline) go through glass transitions . The glass-transition temperature ( T g )

10074-477: The center, flanked on either side by three Apostles. Four streams flowed from the little mountain supporting Christ. The original 5th-century apse mosaic of the Santa Sabina was replaced by a very similar fresco by Taddeo Zuccari in 1559. The composition probably remained unchanged: Christ flanked by male and female saints, seated on a hill while lambs drinking from a stream at its feet. All three mosaics had

10212-476: The continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene ('polythene' in British English), whose repeat unit or monomer is ethylene . Many other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen

10350-665: The decoration scheme first used in Emperor Basil I 's Nea Ekklesia . Not only this prototype was later totally destroyed but each surviving composition is battered so it is necessary to move from church to church to reconstruct the system. An interesting set of Macedonian-era mosaics make up the decoration of the Hosios Loukas Monastery. In the narthex there is the Crucifixion, the Pantokrator and

10488-536: The degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers. Polymers with

10626-400: The driving force for mixing is usually entropy , not interaction energy. In other words, miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction, but because of an increase in entropy and hence free energy associated with increasing the amount of volume available to each component. This increase in entropy scales with

10764-400: The earliest mosaics were made of natural pebbles, originally used to reinforce floors. Mosaic skinning (covering objects with mosaic glass) is done with thin enameled glass and opaque stained glass. Modern mosaic art is made from any material in any size ranging from carved stone, bottle caps, and found objects. The earliest known examples of mosaics made of different materials were found at

10902-423: The episcopal complex were also decorated with mosaics as new finds, that were unearthed in the 2000s, attest. The funerary basilica of Saint Victor , built in a quarry outside the walls, was decorated with mosaics but only a small fragment with blue and green scrolls survived on the intrados of an arch (the basilica was later buried under a medieval abbey). A mosaic pavement depicting humans, animals and plants from

11040-646: The famous Bikini Girls , showing women undertaking a range of sporting activities in garments that resemble 20th Century bikinis . The peristyle , the imperial apartments and the thermae were also decorated with ornamental and mythological mosaics. Other important examples of Roman mosaic art in Sicily were unearthed on the Piazza Vittoria in Palermo where two houses were discovered. The most important scenes there depicted are an Orpheus mosaic , Alexander

11178-417: The field of organic electronics . Nowadays, synthetic polymers are used in almost all walks of life. Modern society would look very different without them. The spreading of polymer use is connected to their unique properties: low density, low cost, good thermal/electrical insulation properties, high resistance to corrosion, low-energy demanding polymer manufacture and facile processing into final products. For

11316-821: The floors of Hellenistic villas and Roman dwellings from Britain to Dura-Europos . Most recorded names of Roman mosaic workers are Greek, suggesting they dominated high quality work across the empire; no doubt most ordinary craftsmen were slaves. Splendid mosaic floors are found in Roman villas across North Africa , in places such as Carthage , and can still be seen in the extensive collection in Bardo Museum in Tunis , Tunisia . There were two main techniques in Greco-Roman mosaic: opus vermiculatum used tiny tesserae , typically cubes of 4 millimeters or less, and

11454-527: The free energy of mixing for polymer solutions and thereby making solvation less favorable, and thereby making the availability of concentrated solutions of polymers far rarer than those of small molecules. Furthermore, the phase behavior of polymer solutions and mixtures is more complex than that of small molecule mixtures. Whereas most small molecule solutions exhibit only an upper critical solution temperature phase transition (UCST), at which phase separation occurs with cooling, polymer mixtures commonly exhibit

11592-401: The glass transition is not. The glass transition shares features of second-order phase transitions (such as discontinuity in the heat capacity, as shown in the figure), but it is generally not considered a thermodynamic transition between equilibrium states. In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect results from the fact that

11730-615: The great baptistries in Ravenna , with apostles standing between palms and Christ in the middle. The scheme is somewhat unusual as the standard post-Iconoclastic formula for domes contained only the image of the Pantokrator . There are very few existing mosaics from the Komnenian period but this paucity must be due to accidents of survival and gives a misleading impression. The only surviving 12th-century mosaic work in Constantinople

11868-530: The hart panteth after the water brooks, so panteth my soul after thee, O God." Water-birds and fish and other sea-creatures can indicate baptism as well as the members of the Church who are christened. Christian mosaic art also flourished in Rome, gradually declining as conditions became more difficult in the Early Middle Ages . 5th century mosaics can be found over the triumphal arch and in the nave of

12006-609: The impostors had cast down here pious emperors have again set up." In the 870s the so-called large sekreton of the Great Palace of Constantinople was decorated with the images of the four great iconodule patriarchs. The post-Iconoclastic era was the heyday of Byzantine art with the most beautiful mosaics executed. The mosaics of the Macedonian Renaissance (867–1056) carefully mingled traditionalism with innovation. Constantinopolitan mosaics of this age followed

12144-415: The individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures. Copolymers are classified either as statistical copolymers, alternating copolymers, block copolymers, graft copolymers or gradient copolymers. In the schematic figure below, Ⓐ and Ⓑ symbolize the two repeat units . Monomers within a copolymer may be organized along

12282-693: The influence of Byzantine art, noticeable on the mosaics of Santa Prassede , Santa Maria in Domnica , Sant'Agnese fuori le Mura , Santa Cecilia in Trastevere , Santi Nereo e Achilleo and the San Venanzio chapel of San Giovanni in Laterano . The great dining hall of Pope Leo III in the Lateran Palace was also decorated with mosaics. They were all destroyed later except for one example,

12420-451: The latter case, increasing the polymer chain length 10-fold would increase the viscosity over 1000 times. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass-transition temperature (T g ). This is a result of the increase in chain interactions such as van der Waals attractions and entanglements that come with increased chain length. These interactions tend to fix

12558-436: The length (or equivalently, the molecular weight) of the polymer chain. One important example of the physical consequences of the molecular weight is the scaling of the viscosity (resistance to flow) in the melt. The influence of the weight-average molecular weight ( M w {\displaystyle M_{w}} ) on the melt viscosity ( η {\displaystyle \eta } ) depends on whether

12696-417: The load is removed. Dynamic mechanical analysis or DMA measures this complex modulus by oscillating the load and measuring the resulting strain as a function of time. Transport properties such as diffusivity describe how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes. The movement of individual macromolecules occurs by

12834-436: The market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur . Ways in which polymers can be modified include oxidation , cross-linking , and end-capping . The structure of

12972-413: The material will endure before failure. This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general, tensile strength increases with polymer chain length and crosslinking of polymer chains. Young's modulus quantifies the elasticity of the polymer. It

13110-414: The mortar base creating a more uniform surface appearance. Decorative patterns are often created by using dividers which creates lines between different colored terrazzo mixtures. Cracking is a common form of failure and is often caused by the structural system that supports the terrazzo rather than the material itself. Contact with alkalis or acids can deteriorate the bonding agents used in terrazzo. As

13248-586: The mosaic floor of the Great Palace of Constantinople which was commissioned during Justinian 's reign. The figures, animals, plants all are entirely classical but they are scattered before a plain background. The portrait of a moustached man, probably a Gothic chieftain, is considered the most important surviving mosaic of the Justinianian age. The so-called small sekreton of the palace was built during Justin II 's reign around 565–577. Some fragments survive from

13386-536: The mosaic of the Exaltation of Adam. In the apse the Ascension of Christ. The Annunciation occupies the two pillars next to the altar." The Daphni Monastery houses the best preserved complex of mosaics from the early Comnenan period (ca. 1100) when the austere and hieratic manner typical for the Macedonian epoch and represented by the awesome Christ Pantocrator image inside the dome, was metamorphosing into

13524-719: The mosaics of this vaulted room. The vine scroll motifs are very similar to those in the Santa Constanza and they still closely follow the Classical tradition. There are remains of floral decoration in the Church of the Acheiropoietos in Thessaloniki (5th–6th centuries). In the 6th century, Ravenna , the capital of Byzantine Italy, became the center of mosaic making. Istria also boasts some important examples from this era. The Euphrasian Basilica in Parentium

13662-406: The most recent, thin set method ( epoxy resin). Bonded terrazzo is applied over a sand-cement mortar underbed which sits on top of a concrete slab. The sand-cement layer allows for variations in the finished concrete slab that it sits on. Monolithic terrazzo is applied directly over an extremely flat and high quality concrete sub-floor. Thin-set terrazzo does not require a concrete sub-floor. Instead,

13800-415: The nine orders of the angels was destroyed in 1822 but other panels survived (Theotokos with raised hands, four evangelists with seraphim, scenes from Christ's life and an interesting Anastasis where King Salomon bears resemblance to Constantine Monomachos). In comparison with Osios Loukas Nea Moni mosaics contain more figures, detail, landscape and setting. Another great undertaking by Constantine Monomachos

13938-444: The number of particles (or moles) being mixed. Since polymeric molecules are much larger and hence generally have much higher specific volumes than small molecules, the number of molecules involved in a polymeric mixture is far smaller than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, is comparable on a per volume basis for polymeric and small molecule mixtures. This tends to increase

14076-725: The old technique. Roman and Byzantine influence led Jewish artists to decorate 5th and 6th century synagogues in the Middle East with floor mosaics. Figurative mosaic, but mostly without human figures, was widely used on religious buildings and palaces in early Islamic art , including Islam's first great religious building, the Dome of the Rock in Jerusalem , and the Umayyad Mosque in Damascus . Such mosaics went out of fashion in

14214-518: The original 4th-century cathedral of Aquileia has survived in the later medieval church. This mosaic adopts pagan motifs such as the Nilotic scene, but behind the traditional naturalistic content is Christian symbolism such as the ichthys . The 6th-century early Christian basilicas of Sant' Eufemia it:Basilica di Sant'Eufemia (Grado) and Santa Maria delle Grazie in Grado also have mosaic floors. In

14352-470: The original decoration, especially a band depicting saints with hands raised in prayer, in front of complex architectural fantasies. In the following century Ravenna , the capital of the Western Roman Empire , became the center of late Roman mosaic art (see details in Ravenna section). Milan also served as the capital of the western empire in the 4th century. In the St Aquilinus Chapel of

14490-719: The partially negatively charged oxygen atoms in C=O groups on another. These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Dipole bonding is not as strong as hydrogen bonding, so a polyester's melting point and strength are lower than Kevlar 's ( Twaron ), but polyesters have greater flexibility. Polymers with non-polar units such as polyethylene interact only through weak Van der Waals forces . As

14628-422: The physical arrangement of monomer residues along the backbone of the chain. These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Various polymer structures can be produced depending on the monomers and reaction conditions: A polymer may consist of linear macromolecules containing each only one unbranched chain. In the case of unbranched polyethylene, this chain

14766-399: The polymer and create gaps between polymer chains for greater mobility and fewer interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC, or unplasticized polyvinylchloride, is used for things such as pipes. A pipe has no plasticizers in it, because it needs to remain strong and heat-resistant. Plasticized PVC is used in clothing for

14904-426: The polymer at the scale of a single chain. The microstructure determines the possibility for the polymer to form phases with different arrangements, for example through crystallization , the glass transition or microphase separation . These features play a major role in determining the physical and chemical properties of a polymer. The identity of the repeat units (monomer residues, also known as "mers") comprising

15042-543: The polymer can lend the polymer to ionic bonding or hydrogen bonding between its own chains. These stronger forces typically result in higher tensile strength and higher crystalline melting points. The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing amide or carbonyl groups can form hydrogen bonds between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to

15180-403: The polymer is above or below the onset of entanglements . Below the entanglement molecular weight , η ∼ M w 1 {\displaystyle \eta \sim {M_{w}}^{1}} , whereas above the entanglement molecular weight, η ∼ M w 3.4 {\displaystyle \eta \sim {M_{w}}^{3.4}} . In

15318-583: The polymerization of PET polyester . The monomers are terephthalic acid (HOOC—C 6 H 4 —COOH) and ethylene glycol (HO—CH 2 —CH 2 —OH) but the repeating unit is —OC—C 6 H 4 —COO—CH 2 —CH 2 —O—, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Synthetic methods are generally divided into two categories, step-growth polymerization and chain polymerization . The essential difference between

15456-686: The pope with a model of the church (destroyed in 1607). The fragment of an 8th-century mosaic, the Epiphany is one of the very rare remaining pieces of the medieval decoration of Old St. Peter's Basilica , demolished in the late 16th century. The precious fragment is kept in the sacristy of Santa Maria in Cosmedin . It proves the high artistic quality of the destroyed St. Peter's mosaics. Mosaics were more central to Byzantine culture than to that of Western Europe. Byzantine church interiors were generally covered with golden mosaics. Mosaic art flourished in

15594-401: The principal door from the narthex we can see an Emperor kneeling before Christ (late 9th or early 10th century). Above the door from the southwest vestibule to the narthex another mosaic shows the Theotokos with Justinian and Constantine . Justinian I is offering the model of the church to Mary while Constantine is holding a model of the city in his hand. Both emperors are beardless – this

15732-408: The richness of God's creation; some elements also have specific connotations. The kantharos vase and vine refer to the eucharist , the symbol of the sacrifice of Christ leading to salvation. Peacocks are symbols of paradise and resurrection; shown eating or drinking from the vase they indicate the route to eternal life. Deer or stags were commonly used as images of the faithful aspiring to Christ: "As

15870-437: The same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents). Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space. The macroscopic physical properties of a polymer are related to the interactions between the polymer chains. When applied to polymers, the term crystalline has a somewhat ambiguous usage. In some cases,

16008-415: The second half of the 5th century. Saint Victor is depicted in the center of the golden dome, while figures of saints are shown on the walls before a blue background. The low spandrels give space for the symbols of the four Evangelists. Albingaunum was the main Roman port of Liguria . The octagonal baptistery of the town was decorated in the 5th century with high quality blue and white mosaics representing

16146-490: The second half of the 6th century. Outstanding examples of Byzantine mosaic art are the later phase mosaics in the Basilica of San Vitale and Basilica of Sant'Apollinare Nuovo. The mosaic depicting Emperor Saint Justinian I and Empress Theodora in the Basilica of San Vitale were executed shortly after the Byzantine conquest. The mosaics of the Basilica of Sant'Apollinare in Classe were made around 549. The anti-Arian theme

16284-512: The size of individual polymer coils in solution. A variety of techniques may be employed for the synthesis of a polymeric material with a range of architectures, for example living polymerization . A common means of expressing the length of a chain is the degree of polymerization , which quantifies the number of monomers incorporated into the chain. As with other molecules, a polymer's size may also be expressed in terms of molecular weight . Since synthetic polymerization techniques typically yield

16422-469: The small tesserae (with sides of 1 mm or less) were set on wax or resin on a wooden panel. These products of extraordinary craftmanship were intended for private devotion. The Louvre Transfiguration is a very fine example from the late 12th century. The miniature mosaic of Christ in the Museo Nazionale at Florence illustrates the more gentle, humanistic conception of Christ which appeared in

16560-471: The so-called Triclinio Leoniano of which a copy was made in the 18th century. Another great work of Pope Leo, the apse mosaic of Santa Susanna , depicted Christ with the Pope and Charlemagne on one side, and SS. Susanna and Felicity on the other. It was plastered over during a renovation in 1585. Pope Paschal I (817–824) embellished the church of Santo Stefano del Cacco with an apsidal mosaic which depicted

16698-448: The states is known as a coil–globule transition . Inclusion of plasticizers tends to lower T g and increase polymer flexibility. Addition of the plasticizer will also modify dependence of the glass-transition temperature T g on the cooling rate. The mobility of the chain can further change if the molecules of plasticizer give rise to hydrogen bonding formation. Plasticizers are generally small molecules that are chemically similar to

16836-402: The surface of finished concrete or epoxy -resin. Much of the preliminary work of terrazzo workers is similar to that of cement masons . Marble-chip, cementitious terrazzo requires three layers of materials. First, cement masons or terrazzo workers build a solid, level concrete foundation that is 3 to 4 inches (76 to 102 mm) deep. After the forms are removed from the foundation, workers add

16974-488: The technique seminato for which workers tossed larger marble chips into the cement that was then ground and polished. Together, these methods create the generic form of terrazzo that involves pieces of stone that are bonded to a cement bed. Terrazzo was first introduced in the United States in the late 1890s, but did not achieve popularity until the 1920s. Until then it was hand polished with a long handled tool called

17112-686: The term crystalline finds identical usage to that used in conventional crystallography . For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography , may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms or more. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions;

17250-460: The terrazzo is thoroughly cured, helpers grind it with a terrazzo grinder , which is somewhat like a floor polisher , only much heavier. Slight depressions left by the grinding are filled with a matching grout material and hand- troweled for a smooth, uniform surface; it is then cleaned, polished, and sealed. Terrazzo installation includes both bonded and unbonded methods. Bonded systems include: bonded underbed, monolithic, chemically bonded, and

17388-641: The tradition in the 6th century, as the mosaics of the Arian Baptistry , Baptistry of Neon , Archbishop's Chapel , and the earlier phase mosaics in the Basilica of San Vitale and Basilica of Sant'Apollinare Nuovo testify. After 539, Ravenna was reconquered by the Romans in the form of the Eastern Roman Empire (Byzantine Empire) and became the seat of the Exarchate of Ravenna . The greatest development of Christian mosaics unfolded in

17526-555: The two is that in chain polymerization, monomers are added to the chain one at a time only, such as in polystyrene , whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in polyester . Step-growth polymerization can be divided into polycondensation , in which low-molar-mass by-product is formed in every reaction step, and polyaddition . Newer methods, such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without

17664-499: The walk honors celebrities in the form of a terrazzo star that displays their name. Archaeologists have adopted the term terrazzo to describe the floors of early Neolithic buildings ( PPNA and PPNB , ca. 9,000–8,000 BC) in Western Asia constructed of burnt lime and clay, colored red with ochre and polished. The embedded crushed limestone gives it a slightly mottled appearance. The use of fire to produce burnt lime, which

17802-595: The world, and are protected as a UNESCO World Heritage Site . The large villa rustica , which was probably owned by Emperor Maximian , was built largely in the early 4th century. The mosaics were covered and protected for 700 years by a landslide that occurred in the 12th Century. The most important pieces are the Circus Scene , the 64m long Great Hunting Scene , the Little Hunt , the Labours of Hercules and

17940-459: Was almost certainly because of nearby Muslims' beliefs. In the Iconoclastic era , figural mosaics were also condemned as idolatry. The Iconoclastic churches were embellished with plain gold mosaics with only one great cross in the apse like the Hagia Irene in Constantinople (after 740). There were similar crosses in the apses of the Hagia Sophia Church in Thessaloniki and in the Church of

18078-576: Was also used for the hafting of implements, predates production of fired pottery by almost a thousand years. In the early Neolithic settlement of Çayönü in eastern Turkey about 90 m (970 sq ft) of terrazzo floors have been uncovered. The floors of the PPN B settlement of Nevalı Çori measure about 80 m (860 sq ft). They are 15 cm (5.9 in) thick, and contain about 10–15% lime. These floors are almost impenetrable to moisture and very durable, but their construction involved

18216-464: Was built in the middle of the 6th century and decorated with mosaics depicting the Theotokos flanked by angels and saints. Fragments remain from the mosaics of the Church of Santa Maria Formosa in Pola . These pieces were made during the 6th century by artists from Constantinople. Their pure Byzantine style is different from the contemporary Ravennate mosaics. Very few early Byzantine mosaics survived

18354-405: Was called asaroton (Greek for "unswept floor"). It depicted in trompe-l'œil style the feast leftovers on the floors of wealthy houses. With the building of Christian basilicas in the late 4th century, wall and ceiling mosaics were adopted for Christian uses. The earliest examples of Christian basilicas have not survived, but the mosaics of Santa Constanza and Santa Pudenziana , both from

18492-605: Was coined in 1833 by Jöns Jacob Berzelius , though with a definition distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger , who spent the next decade finding experimental evidence for this hypothesis. Polymers are of two types: naturally occurring and synthetic or man made . Natural polymeric materials such as hemp , shellac , amber , wool , silk , and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose , which

18630-554: Was laid on site. There was a distinct native Italian style using black on a white background, which was no doubt cheaper than fully coloured work. In Rome, Nero and his architects used mosaics to cover some surfaces of walls and ceilings in the Domus Aurea , built 64 AD, and wall mosaics are also found at Pompeii and neighbouring sites. However it seems that it was not until the Christian era that figural wall mosaics became

18768-417: Was produced in workshops in relatively small panels which were transported to the site glued to some temporary support. The tiny tesserae allowed very fine detail, and an approach to the illusionism of painting. Often small panels called emblemata were inserted into walls or as the highlights of larger floor-mosaics in coarser work. The normal technique was opus tessellatum , using larger tesserae, which

18906-449: Was the church of San Giovanni Evangelista . She erected it in fulfillment of a vow that she made having escaped from a deadly storm in 425 on the sea voyage from Constantinople to Ravenna. The mosaics depicted the storm, portraits of members of the western and eastern imperial family and the bishop of Ravenna, Peter Chrysologus . They are known only from Renaissance sources because almost all were destroyed in 1747. Ostrogoths kept alive

19044-544: Was the restoration of the Church of the Holy Sepulchre in Jerusalem between 1042 and 1048. Nothing survived of the mosaics which covered the walls and the dome of the edifice but the Russian abbot Daniel, who visited Jerusalem in 1106–1107 left a description: "Lively mosaics of the holy prophets are under the ceiling, over the tribune. The altar is surmounted by a mosaic image of Christ. In the main altar one can see

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