Mosaic

Mosaic (corresponding to Lat. opus musivum, from Gr. µova-€ ov, an artificial grotto often decorated with mosaics; the word is only found in the sense of mosaic in late Greek, which generally uses Ikn oXayfµa), the fitting together of many, generally small, pieces of marble, opaque glass, coloured clays, or other substances, so as to form a pattern.

Ancient Mosaic

The earliest existing specimens of mosaic belong to one of the less important branches of the art - namely, the ornamentation on a small scale of jewellery, ivory thrones, and other furniture, or more rarely of some elaborate architectural ornament. Most of this sort of mosaic resembles in execution what are called cloisonné enamels. In the Louvre and in the British Museum are preserved some very beautiful ivory carvings in low relief, some from Nineveh and others from Egypt, in which figures of deities, ornaments formed of the lotus and papyrus plants and royal cartouches are enriched by small pieces of glass or lapis-lazuli and other gem-like stones, which are let into holes made in the ivory. Each minute piece is separated from the next by a thin wall or cloison of ivory, about as thick as cardboard, which thus forms a white outline and setsoff the brilliance of the coloured stones.

Excavations at Tel-el-Yehudia in Lower Egypt have brought to light some mosaics on a larger scale, but treated in the same way. These are caps of columns, wall tiles, and other objects, either of white limestone or earthenware, in which designs, chiefly some forms of the papyrus, are formed by bits of glass or enamelled earthenware, let into a sinking in the tile or column. This form of mosaic was employed by the Greeks: the Erechtheum at Athens, built in the middle of the 5th century B.e., had the bases of some of its white marble columns ornamented with a plait-like design, in which pieces of coloured glass were inserted to emphasize. the main lines of the pattern.

Another, quite different, sort of mosaic was known to the Egyptians of the Ptolemaic and Roman periods. This is made entirely of glass and is extremely minute. The finest known specimen is in the British Museum: it is a small tablet about in. square, apparently the bezel of a ring, on which is represented the sacred hawk - every feather on the bird's wing being produced with a great number of colours and tints, each quite distinct, and so minute that a strong magnifying glass is required to distinguish its details, The way in which this mosaic was produced is extremely ingenious. Numbers of long sticks of various-coloured glass were arranged in such a way that their ends produced the figure of the hawk; other sticks of blue glass were placed all round so as to form the ground. The whole bundle of sticks of glass when looked at endwise now presented the figure of the hawk with a blue background, immensely larger than it afterwards became. The bundle was then heated till the sticks melted together, and the whole thick rod, softened by fire, was drawn out to a greatly diminished thickness. A slice of the rod was then cut off and its faces polished - the design, much reduced in size, of course being equally visible at both sides of the slice; and thus the microscopic minuteness of the mosaic was produced with astonishing delicacy and refinement; many slices, each showing the same mosaic, could be cut from the same rod.

Far more important was the use of mosaic on a large scale, either for pavements or for walls and vaulted ceilings. We are told by Pliny (H. N. xxxvi. 184) that the practice of decorating pavements " after the fashion of painting " was due to the Greeks, and there is no reason to doubt the truth of this statement, although no mosaic pavement discovered in Greece can be dated with certainty to a period preceding the Roman occupation. This is true even of the pavement in the temple of Zeus I at Olympia (fig. 1; Olympia, Baudenkmiiler, vol. ii. pl. cv.).

The simplest classification of mosaics is that of Gauckler (Daremberg and Saglio, Dictionnaire des antiquites, s.v. " Musivum Opus "), who distinguishes the following: a. Opus tessellatum, consisting of cubes of marble or stone, regularly disposed in simple patterns. This was largely used for pavements, especially in Roman times.

b. Opus vermiculatum, consisting of cubes (not always regularly shaped) generally of coloured marble' or more precious FIG. I. - Greek Pavement from the Temple of Zeus at Olympia.

materials, when these were obtainable, disposed so as to obtain a pictorial effect. The art of mosaic is mainly concerned with this branch of work.

c. Opus musivum, properly applied to the mosaic decoration of walls and vaulted ceilings (camerae), in which cubes of glass or enamel were used. The glass was rendered opaque by the addition of oxide of tin, and coloured with other metallic oxides; when melted it was cast into flat slabs, generally about 2 in. thick, and then broken into small cubes.

d. Opus sectile, a species of marqueterie in marble or other coloured materials used to produce pictures and patterns. Under the later empire a particular variety of this, called opus alexandrinum 2 mainly composed of porphyry, red and green,' was much in use.

Judging from the description given by Vitruvius (vii. I), and an examination of numerous specimens of Roman tessellated mosaics, the process of manufacture was the following. The earth was first carefully rammed down to a firm and even surface; on this was laid a thick bed of stones, dry rubbish, and lime, called " rudus," from 6 to 9 in. deep, and above this another layer, 4 to 6 in. thick, called " nucleus," of one part of lime to three of pounded brick, mixed with water; on this, while still soft, the pattern could be sketched out with a wooden or metal point, and the tesserae or small bits of marble stuck into it, with their smoothest side uppermost. Lime, pounded white marble, and water were then mixed to the consistency of cream, forming a very hard-setting cement, called marmoratum. This cement, while fluid, was poured over the marble surface, and well brushed into all the interstices between the tesserae. When the concrete and cement were both set, the surface of the pavement was rubbed down and polished.

The usual Roman pavement was made of pieces of marble, averaging from half to a quarter of an inch square, but rather 1 In the less prosperous provinces of the empire, such as Britain, these costly materials could not be obtained, and native sandstone, &c., was used.

The biographer of Severus Alexander (Hist. Aug., c. 2 5, 7) attributes the invention of opus alexandrinum to that emperor; but this is clearly a false derivation. This technique was doubtless invented at Alexandria.

This latter is often, but wrongly, called serpentine.

irregular in shape. A few other, but quite exceptional, kinds of mosaic pavements have been found, such as that at the Isola Farnese, 9 m. from Rome, made of tile-like slabs of green glass, and a fine " sectile " pavement on the Palatine Hill, made of various-shaped pieces of glass, in black, white, and deep yellow. In some cases - e.g. in the " House of the Faun " at Pompeii - glass tesserae in small quantities have been mixed with the marble ones, for the sake of greater brilliance of colour.

Few countries are richer than England in remains of Roman mosaics; the great pavements of York, Woodchester, Cirencester, and many other places are as elaborate in design and as skilfully executed as any that now exist even in Rome itself. In whatever country these mosaics are found, their style and method of treatment are always much the same; the materials only of which the tesserae are made vary according to the stone or marble supplied by each country. In England, for instance, limestone or chalk often takes the place of the white marble so common in Italian and North African mosaics; while, instead of red marble, a fine sort of burnt clay or red sandstone is generally used; other makeshifts had to be resorted to, and many of the Romano-British mosaics are made entirely without marble. It is perhaps partly owing to the great wealth of Northern Africa in marbles of many colours and of varying shades that the finest of all Roman mosaics have been found in Algeria and Tunis, especially those from Carthage, some of which have been brought to the British Museum. See Archaeologia, xxxviii. 202.

The range of colour in the marble tesserae is very great, and is made use of with wonderful taste and skill: there are three or four different shades of red, and an equal number of yellows and greens, the last colour in all its tints being almost peculiar to this part of Africa, and one of the most pleasant and harmonious in almost any combination. Deep black, browns and FIG. 2. - Part of a Persian's Head from the Battle of Issus; full size.

bluish-greys are also abundant. The mosaics from Carthage are no less excellent in design than in the richness and beauty of their materials. Large spaces are filled by grand sweeping curves of acanthus and other leaves, drawn with wonderful boldness and freedom of hand, and varied with great wealth of invention. Without the use of very small tesserae, much richness of effect is given by gradations of tints, suggesting light and .InntYf MTV1TRtiITiTVtTTY1TTMiT1111t1tiMt'rtv?,  ? C -.9.@i ° ..., i??? ?,?

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The finest of the later examples in Rome is that which decorates the vault of the ambulatory of the circular church of S. Costanza, built by Constantine the Great, outside the walls of Rome. This very interesting mosaic might from its style and materials have been executed in the 1st century, and is equal in beauty to any work of the kind in Italy. It shows no trace whatever of the Byzantine influence which, in the next century, introduced into Italy a novel style of mosaic, in materials of the most glittering splendour. Survivals of this classical style of mosaic are found in North Africa and the East. At Kabr-Hiram, near Tyre, Renan discovered among the ruins of a small three-apsed Christian church of the 4th century A.D. a fine mosaic pavement, covering the nave and aisles, thoroughly classical in style. A very similar mosaic, of about the same date, was discovered at Nebi Yunas, near Sidon.

Medieval Mosaics

These may be divided into four principal classes: (r) those used to decorate walls and vaults, made of glass cubes; (2) those for pavements, made of marble, partly in large shaped pieces, and partly in small tesserae; (3) glass in small pieces, either rectangular or triangular, used to enrich marble pulpits, columns, and other architectural features; (4) wood mosaics.

i. In the Byzantine period the glass cube mosaic was exclu sively employed in mural decoration. At first natural colouring was used, and backgrounds, if not in local colour, were generally blue; but the use of gold, both for backgrounds and for the high lights on drapery, &c., gradually prevailed. Owing to the intense conservatism of Byzantine art, no regular stages of progression can be traced in this class of mosaic. Some of the 5th-century mosaics at Ravenna are, in every way, as fine as those of the 12th, and it was not till the end of the 13th century that any important change in style took place. The mosaics of the 9th century are inferior in drawing and general treatment to those both of the earlier and later time, while in Italy at least this art was almost entirely extinct during the 10th and rrth centuries. Extreme splendour of colour and jewel-like brilliance combined with the most stately grandeur of form are the main characteristics of this sort of decoration.

A " majesty," or colossal central figure of Christ with saints standing on each side, is the most frequent motive. In many cases, especially in the 5th and 6th centuries, Christ was represented as a lamb, to whom the twelve apostles, in the form of sheep, are paying adoration. Christ, the Good Shepherd, is sometimes depicted as a beardless youth, seated among a circle of sheep - the treatment of the motive being obviously taken from Pagan representations of Orpheus playing to the beasts. The tomb of Galla Placidia has a good example of this subject, with much of the old Roman grace in the drawing and composition. Frequently the Virgin Mary, or the patron saint of the church, occupies the central space in the apse, with ranges of other saints on each side.

The " Doom," or Last Judgment, is a favourite subject for domes and sanctuary arches; the Florence baptistery has one of the grandest mosaic pictures of this subject, executed in the 13th century. The earlier baptisteries usually have the scene of Christ's baptism - the river Jordan being sometimes personified in a very classical manner, as an old man with flowing beard, holding an urn from which a stream pours forth. S. Vitale at Ravenna has in the sanctuary a very interesting representation of Justinian and his empress Theodora (see fig. 3), attended by a numerous suite of courtiers a. nd ladies; these mosaics are certainly of the 6th century, and may be contemporary with Justinian, though the fact that he and Theodora are each represented with a circular nimbus appears to indicate that they were not then alive.

In mosaics of the best periods the treatment of the forms and draperies is broad and simple, a just amount of relief being expressed by delicate gradations of tints. In mosaics of the 9th century the drawing is very awkward, and the folds of the robes are rudely expressed in outline, with no suggestion of light and shade.

A further application of this work was to the decoration of broad bands over the columns of the nave, as at S. Maria Maggiore in Rome, 4th century, and in the two churches of S. Apollinare at Ravenna, 6th century. In some cases almost the whole interior of the church was encrusted in this magnificent way, as at Monreale Cathedral, the Capella Palatina of Palermo, and S. Mark's at Venice.

In these churches the mosaics cover soffits and angles entirely, and give the effect of a mass of solid gold and colour producing the utmost conceivable splendour of decoration.' In many cases vaulted ceilings were covered with these mosaics, as the tomb of Galla Placidia, A.D. 450, and the two baptisteries at Ravenna, 5th and 6th centuries. For exteriors, the large use of mosaic was usually confined to the west facade, as at S. Miniato, Florence; S. Maria Maggiore, Rome; and S. Mark's, FIG. 3. - Mosaic of Theodora and Attendants, from S. Vitale, Ravenna; over life size.

Venice. In almost all cases the figures are represented on a gold ground, and gold is freely used in the dresses and ornaments - rich jewels and embroidery being represented in gold, silver, sparkling reds, blues and other colours, so as to give the utmost splendour of effect to the figures and their drapery.

The revival of the art of painting in Italy and the introduction of fresco work in the r4th century gave the deathblow to the ' Unfortunately the world-wide fame of S. Mark's and the other great churches of Italy has subjected these extraordinary works to the fatal process of " restoration," and wherever any sign of decay in the cement backing (the tesserae themselves are quite indestructible) has given the least excuse the " restorers " have destroyed whole masses of ancient work, and supplied its place with worthless modern copies. The mosaics of the S. Mark's baptistery, and of the apses at S. Miniato, at Pisa, and many other places have in this way been wantonly renewed in recent times.

true art of wall-mosaics. Though at first the simple and archaic style of Cimabue and his pupils Jacopo da Turrita, Giotto, and Taddeo Gaddi was equally applicable to painting or mosaic, yet soon the development of art into greater realism and complexity required a method of expression unfettered by the necessities and canons of mosaic work. Pietro Cavallini, a Roman artist, was one of the last who worked according to the old traditions. His mosaic of the birth of the Virgin in S. Maria in Cosmedin, Rome, executed about the middle of the 14th century, is not without merit, though his superior knowledge of form has only caused his composition to be somewhat feeble and insipid compared with the works of the earlier artists. Even in the 15th century a few good mosaics were produced at Venice and elsewhere. The mosaics from Titian's pictures on the west end of S. Mark's at Venice, Raphael's in the Chigi Chapel in S. Maria del Popolo, and many large pictures in S. Peter's in Rome are the most striking examples of these.

The following list, in chronological order, comprises a selection from among the most important glass wall-mosaics during the period when mosaic-working was a real art.' 4th Century. S. Costanza.

S. Maria Maggiore - square columns of the nave.

S. Pudenziana.

S. Giovanni in Laterano - chapel of SS. Rufina e Seconda.

S. Restituta - baptistery.

5th Century. Orthodox Baptistery - vault.

Tomb of Galla Placidia - vault, 450. Archbishop's Chapel - vault.

S. Paolo fuori le mura - triumphal arch.

S. Maria Maggiore - square pictures over nave columns, and triumphal arch (?).

S. Sabina - figures on west wall.

S. Ambrogio, Chapel of S. Satiro - vault. Cathedral - apse.

Cathedra

apse.

6th Century. Arian Baptistery - vault.

S. Apollinare Nuovo - apse and nave, with 9thcentury additions.

S. Vitale - apse and whole sanctuary, c. 547. S. Apollinare in Classe - apse and nave, 549. SS. Cosmas and Damian - apse.

S. Lorenzo, Chapel of S. Aquilinus - vault. S. Sophia - walls and vault, c. 550.

Church of St George - apse, &c.; and S. Sophia - dome and apse.

S. Sophia - apse.

7th Century. S. Agnese fuori le mura - apse, 626.

S. Teodoro.

S. Stefano Rotondo.

S. Venanzio, baptistery of Lateran.

" Dome of the Rock " - arches of ambulatory, 688.

8th Century. Baptistery of S. Giovanni in Laterano.

SS. Nereus and Achilles.

Mosque of Al-Aksa - on dome.

Chapel of the Transfiguration.

gth Century. S. Cecilia in Trastevere - apse.

S. Marco - apse.

S. Maria della Navicella - apse, and " Chapel of the Column." S. Prassede - triumphal arch.

S. Ambrogio - apse, 832.

loth Century. Cordova. Mihrab (sanctuary) of Mosque.

11th Century. Jerusalem. " Dome of the Rock " - base of cupola, 1027. Constantinople. Church of S. Saviour - walls and domes. 12th Century. Venice. S. Mark's - narthex, apse and walls of nave and aisles.

1 It must be remembered that the earlier mosaics have in most cases suffered much from restoration.

Cathedra

apse. Cathedral - apse. Cathedral - apse. Cathedral - apse.

Capella Palatina, begun 1132 - the whole walls. Church of La Martorana - vault. Cathedral - the whole walls, 1170-1190.

Church of the Nativity, 1169.

Cathedra

apse, 1148.

S. Clemente - apse.

S. Francesca Romana - apse.

S. Maria in Trastevere - apse.

13th Century. Baptistery vault, begun c. 1225 by Fra Jacopo. S. Miniato - apse and west front.

S. Paolo fuori le mura - apse.

S. Clemente - triumphal arch, 1297.

S. Giovanni in Laterano - apse by Jacopo da Turrita, 1290.

S. Maria Maggiore - apse and west end by Jacopo da Turrita and Taddeo Gaddi.

S. Maria in Trastevere - apse by Pietro Cavallini, 1291.

14th Century. Florence. Baptistery, finished by Andrea Tafi.

Pisa. Cathedral - east apse by Cimabue, 1302, north and south apses by his pupils.

Rome. S. Peter's - navicella, in atrium by Giotto.

S. Maria in Cosmedin - on walls by Pietro Cavallini, c. 1340.

Venice. SS. Giovanni e Paolo - in arch over effigy of Doge Morosini.

The Byzantine origin of these great wall-mosaics, wherever they are found, is amply proved both by internal and documentary evidence. The gorgeous mosaics of S. Sophia and S. Saviour's in Constantinople, 6th century, and the later ones in the monasteries of Mount Athos, at Salonica and at Daphne near Athens, are identical in style with those of Italy of the same date. Moreover, the even more beautiful mosaic work in the " Dome of the Rock " at Jerusalem, 7th and 11th centuries, and that in the sanctuary of the great mosque of Cordova, of the 10th century, are known to be the work of Byzantine artists, in spite of their thoroughly Oriental design. The same is the case with the rarer mosaics of Germany,. such as those in S. Gereon at Cologne and at Parenzo.

A very remarkable, almost unique, specimen of Byzantine mosaic is now preserved in the " Opera del Duomo," Florence. This is a diptych of the 11th century, of extremely minute, almost microscopic work, in tesserae of glass and metal, perhaps the only example of tesserae made of solid metal. It has figures of saints and inscriptions, each tessera being scarcely larger than a pin's head. This beautiful diptych originally belonged to the imperial chapel in Constantinople, and was brought to Florence in the 14th century.

2. The second medieval class, mosaic pavements, though of great beauty, are of less artistic importance. This so-called opus alexandrinum is very common throughout Italy and in the East, and came to greatest perfection in the 13th century. It is made partly of small marble tesserae forming the main lines of the pattern, and partly of large pieces used as a ground FIG. 4. - Marble Mosaic at Monreale Cathedral.

or matrix. It is generally designed in large flowing bands which interlace and enclose circles, often of one stone sliced from a column. The finest example is that at S. Mark's, Venice, of the 12th century. The materials are mainly white marble, with green and red porphyry, and sometimes glass.

Capua. Torcello. Murano. Salerno. Palermo. Monreale. Bethlehem. Cefalu. Rome. ' Florence. Rome. Rome. Naples. Ravenna. Rome. Milan. Fundi. Nola. Ravenna. Rome. Milan. Constantinople. Thessalonica. Trebizond. Rome. Jerusalem. Rome. Jerusalem. Mount Sinai. Rome. Milan. panels over the Besides the countless churches in Italy possessing these beautiful pavements, such as S. Lorenzo, S. Marco, S. Maria Maggiore, and S. Maria in Trastevere, in Rome, there are in England, in the Chapel of the Confessor, and in front of the high altar at Westminster, very fine specimens of this work, executed about 1 268 by a Roman artist called Odericus, who was brought to England by Abbot Ware, on the occasion of a visit made by the latter to Rome. Another English example is the mosaic pavement in front of the shrine of Becket at Canterbury; this is probably the work of an Englishman, though the materials are foreign, as it is partly inlaid with bronze, a peculiarity never found in Italy. Palermo and Monreale are especially rich in examples of sectile mosaic, used both for pavements and walls - in the latter case generally for the lower part of the walls the upper part being covered with the glass mosaics. Fig. 4 gives a specimen of this mosaic from Monreale cathedral. Its chief characteristic is the absence of curved lines, so largely used in the splendid opus Alexandrinum of Italy, arising from the fact that this class of Oriental design was mainly used for the delicate panelling in wood on their pulpits, doors, &c. - wood being a material quite unsuited for the production of large curves.

3. Glass mosaic, used to ornament ambones, pulpits, tombs, bishops' thrones, baldacchini columns, architraves, and other marble objects, is chiefly Italian. The designs, when it is used to enrich flat surfaces, such as panels or architraves, areverysimilar to those of the pavements last described. The white marble is used as a matrix, in which sinkings are made to hold the glass tesserae; twisted columns are frequently ornamented with a spiral band of this glass mosaic, or flutings are suggested by parallel bands on straight columns. The cloisters of S. Giovanni in Laterano and S. Paolo fuori le mura have splendid examples of these enriched shafts and architraves.

This style of work was largely employed from the 6th to the 14th centuries. One family in Italy, the Cosmati, during the whole of the 13th century, was especially' skilled in this craft. The pulpit in S. Maria in Ara Coeli, Rome, is one of the finest specimens (see fig. 5), as are also the ambones in S. Clemente and S. Lorenzo, and that in Salerno cathedral. The tomb of Henry III. (1291), and the shrine of the Confessor (1269) at Westminster are the only examples of this work in England. They were executed by " Petrus civis Romanus," probably a pupil of the Cosmati.

In India, especially during the 17th century, many Mahommedan buildings were decorated with fine marble inlay of the class now called " Florentine." This is sectile mosaic, formed by shaped pieces of various coloured marbles let into a marble matrix. A great deal of the Indian mosaic of this sort was executed by Italian workmen; the finest examples are at Agra, such as the Taj Mahal.

4. Mosaics in wood are largely used in Mahommedan buildings, especially from the 14th to the 17th centuries. The finest specimens of this work are at Cairo and Damascus, and are used chiefly to decorate the magnificent pulpits and other woodwork in the mosques. The patterns are very delicate and complicated, worked in inlay of small pieces of various coloured woods, often further enriched by bits of mother-of-pearl and minutely carved ivory. This art was also practised largely by the Copts of Egypt, and much used by them to ornament the magnificent iconostases and other screens in their churches.

Another application of wood to mosaic work, called " intarsiatura," was very common in Italy, especially in Tuscany and Lombardy, during the i 5th and early 16th centuries. Its chief use was for the decoration of the stalls and lecterns in the church choirs. Very small bits of various coloured woods were used to produce geometrical patterns, while figure subjects, views of buildings with strong perspective effects, and even landscapes, were very skilfully produced by an inlay of larger pieces. Ambrogio Borgognone, Raphael, and other great painters, often drew the designs for this sort of work. The mosaic figures in the panels of the stalls at the Certosa near Pavia were by Borgognone, and are extremely beautiful. The stalls in Siena cathedral and in S. Pietro de' Casinensi at Perugia, the latter from Raphael's designs, are among the finest works of this sort, which are very numerous in Italy. It has also been used on a smaller scale to ornament furniture, and especially the " Cassoni," or large trousseau coffers, on which the most costly and elaborate decorations were often lavished.

Authorities

- Classical. An excellent account of the subject, with full references, is given by Gauckler in Daremberg and Saglio, Dictionnaire des antiquites, s.v. " Musivum opus "; the translations there given of the loci classici of Pliny are, however, inaccurate. Amongst earlier works the following are important: G. Ciampini, Vetera monumenta (1690-1699); A. Furietti, De musivis (1752); S. Lysons, Roman Antiquities of Woodchester (1797) and Reliquiae britannico-romanae (1813); F. Mazois, Ruines de Pompei (1812-1838); Real museo borbonico (1824-1857); F. Artaud, Histoire de la peinture en mosaique (1835); Monumentos arquitectonicos de Espana (1859-1883); Wilmowsky, Riimische Mosaiken aus Trier and dessen Umgegend (1888).

Christian

Theophilus, Diversarum artium schedula, ii. 15; S. Kensington Museum Art Inventory, pt. i. (1870); Renan, Mission de Phenicie (1875); Garrucci, Arte cristiana (1872-1882), vol. iv.; De Rossi, Musaici cristiani di Roma (1876-1894); Parker, Archaeology of Rome, and Mosaic Pictures in Rome and Ravenna (1866); Barbet de Jouy, Les Mosaiques chretiennes de Rome (1857); Gravina, Duomo di Monreale, Palermo (1859 seq.); Serradifalco, Monreale ed altre chiese siculo-normanne (1838); Salazaro, Mon. dell' arte merid. d'Italia (1882); M. D. Wyatt, Geometrical Mosaics of the Middle Ages (1849); Salzenberg, Alt-christliche Baudenkmale von Constantinopel (1854); Pulgher, Eglises byzantines de Constantinople (1883); Texier and Pullan, Byzantine Architecture (1864); Quast, Alt-christliche Bauwerke von Ravenna (1842);- J. P. Richter, Die Mosaiken von Ravenna (1878); M. de Vogue, Eglises de la terre sainte (1860); Milanesi, Del Arte del vetro pel musaico (16th century, reprinted at Bologna in 1864); Rohault de Fleury, Monuments de Pise (1866); J. Kreutz, Basilica di S. Marco, Venezia (1843); Gaily Knight, Ecclesiastical Architecture of Italy (1842-1844); C. G. Fossati, Aya Sophia (1852); A. N. Didron, " La peinture en mosaique," Gaz. des B. Arts, xi. 442; Gerspach, La Mosatique (1883); A. L. Frothingham, " Les mosaiques de Grottaferrata," Gaz. arch. (1883); E. Miintz, La Mosaique chretienne pendant les premiers siecles (1893); G. Clausse, Basiliques et mosaiques chretiennes (1893); Ainalov, Mosaiken des IV. u. V. Jahrhunderts (1895); P. Saccardo, Les Mosaiques de Saint Marc d Venise (1896); A. A. Pavlovsky, Iconographie de la chapelle palatine (1895); Di Marzo, Delle Belle arti in Sicilia; Sangiorgi, Il Battistero della basilica Ursiana di Ravenna (1900); J. Kurth, Die Mosaiken der christlichen Aera, I. Die Mosaiken von Ravenna (1902); J. P. Richter and A. C. Taylor, The Golden Age of Classic Christian Art (1904; on the mosaics of S. Maria Maggiore, which the authors assign to the 2nd or 3rd century A.D.; some excellent reproductions are given); Schmitt and Kluge, " Kachrie Djami " (Bulletin de l'institut imperiale russe a Constantinople, xi., 1906; text in Russian).

Moslem

Hessemer, Arabische and alt-italienische Bauverzierungen (1853); Prisse d'Avennes, L' Art arabe (1874-1880); Prangey, Mosquee de Cordoue (1830); Owen Jones, Alhambra (1842); De Vogue, Temple de Jerusalem (1864); Texier, Asie Mineure (1862) and L'Armenie et la Perse (1842-1852); Bourgoin, Les Arts arabes (1868); Coste, Monuments modernes de la Perse (1867); Flandin and Coste, Voyage en Perse (1843-1854); Gayet, L' Art arabe (1893).

Wood Mosaic-Tarsia

Omati del coro di S. Pietro Cassinense di Perugia (1830); Caffi, various works on Rafaello de Brescia and other intarsiatori (1851); Tarsie ed intagli di S. Lorenzo in Genova (1878); and Scherer, Technik and Geschichte der Intarsia (1891).

(J. H. M.; H. S. J.)

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1.1" --??; ?ilil' Inif  ?- i ?I. l i :... l 01[[Immo„ W]]?kluAvoli t, FIG. 5. - Part of Marble Pulpit with glass mosaic, church of Ara Coeli, Rome.

ll_ Modern Mosaic. - The art of mosaic for mural decoration has never been deeply implanted in the artistic sensibilities of the north of Europe, nor has it been employed much either in France, or Germany, or England. It ceased to be generally adopted in Italy when fresco, oil and tempera painting came into vogue. Gothic architecture is ill-suited to its robust claims as a decorative art; and the incoming fashion for the latest and least interesting development of classical architecture, " Palladian," divorced not only it, but mural painting also, from all architectural schemes. To be properly consequent and effective, buildings, ecclesiastical or public, should be constructed with the intention of being covered almost entirely by mosaics, which demand rich environment, marble or other colour; mosaic is essentially a colour medium. It is therefore scarcely surprising that when mural decoration became preeminently pictorial, and gestures and expression grew complicated, elaborate, and naturalistic, an art limited in its powers of presenting such manifestation of realistic design was relegated into the limbo of obscurity.

There are no instances of the use of mosaic in England after the Roman occupation. The Normans, who derived it from the Greeks and Saracens, and adopted it in Sicily, did not import it either to France or England. Although English churches, and French also, were highly decorated with polychromy from early times up to the r 6th century, there is no evidence of mosaic ever having been used. The revival of a school of mosaicists in Rome during the 17th century, employed in the decoration of St Peter's, and here and there sparsely engaged in other churches, led to the idea which Wren would have carried into effect, namely, making use of mosaic for the cathedral of St Paul's in London; but his scheme, if it was ever really entertained, was not carried out, as we all know; and the art, which might have become the fashion in England, remained an exotic. Even late into the years of the r9th century mosaic decoration was regarded by classical purists as a barbarous art, and the glorious decorations in that material to be seen in Sicily, Italy, Greece, Asia Minor and Russia were disregarded as works of high art. They were in many cases cut out to provide room for extravagant and vulgar designs in fresco or tempera, unmeaning, undecorative, and wholly abominable as decoration. Those Roman mosaics over the altars in St Peter's, being copies of celebrated oil pictures, while they cannot be denied excellence as such and marvellous dexterity, reveal the worst possible taste, for they attempt to represent adequately, in cubes, touches of the brush which were spontaneous, fluid, thick and thin, and as sensitive and spontaneous as the finger pressure on the violin string, so accurate that the least deviation from absolute position produces discord.

The restrictions on mosaic are many, and some are obvious. In the first place, mosaic is not suited for a small scale of design. It is true that in the Opera del Duomo in Florence there is a miniature mosaic (executed in the r 2th century) of extraordinary beauty, which must have taken a lifetime to execute; but still this remains a curiosity, a bit of craftsmanship rather than a great work of art. There is also a copy of Mr Holman Hunt's " Finding the Saviour in the Temple," executed for Clifton College by assistants in Messrs Powell's establishment in Whitefriars, London; it is admirably done, no doubt, but it is a long way behind the original, which is a design wholly ill adapted to mosaic. There are several other instances, notably one by Mr H. Holiday of " The Last Supper," where mosaic has been employed to translate a beautiful design which would have been more satisfactorily executed either in oil or water colours. The primal and most obvious limitation is in matters of detail - detail as regards a multiplicity of forms, many gradations either of colour or tone and naturalistic accidents. In this respect good mosaic is like good basso relievo; it is accomplished by firmly pronounced outlines, unconfused masses, large planes unbroken up by small adjuncts, and generalized and conventionalized forms and simple colour. So all small curves, as well as small tints, should be eliminated, because it is not in the nature of the material to do them justice. One can scarcely conceive a choice less happy for mosaic than the centre group taken out of the upper portion of the Disputa fresco in the Vatican by Raphael, yet this florid piece of work, so facile in creation, was chosen to be executed on the eastern wall of the morning chapel in St Paul's.

It is useless to illustrate the many similar mistakes that have been made. They were made in some of the earlier work in the choir of St Paul's. The best example of mosaic on a small scale is in Ravenna, the tomb of Galla Placidia; the best upon a large scale is the great Christ at the east end of the cathedral at Monreale. These two works absolutely justify the means to the end. Interesting are the designs made by Sir Edward BurneJones for the mosaics for the American church in Rome, but the execution and colour are alike monotonous. The cathedral of Chester contains a series of mosaic pictures designed by Mr Clayton. The Guards' chapel in St James's is adorned likewise by the same artist, under the direction of the late Sir Arthur Blomfield. In the chapel for the school at Giggleswick are mosaics designed by T. G. Jackson, R.A., admirably and broadly treated in true mosaic character; these were executed in situ, and not, according to the modern habit, upon paper, away from their environment and by a foreign firm. Those mosaic pictures which are placed in niches in the great gallery of South Kensington Museum are failures qud mosaic, though the designs in many instances are fine, notably those by Lord Leighton and Val Prinsep; but their execution is uninteresting, because the cubes are laid so flatly and so evenly that they suggest an oil picture appliqué upon a flat ground.

Messrs Powell have been employed on several occasions to decorate churches with mosaic. This firm has adopted the old style, and rejected the new one initiated by Dr Salviati of Venice. If we observe the surface of a fine Greek mosaic, such as that of Andrea Tafi in the Baptistery of Florence, or the few remains of unrestored mosaic in St Mark's, Venice, or indeed other works scattered over Italy, we shall see that it is rough, not smooth; that the cubes are irregular in shape; that there is always a space of the ground colour left, red or white, and visible between each cube. In modern mosaic, with rare exceptions, restoration or other, the cubes have been jammed up closely together, and the surface is as smooth as a piece of paper; thereby is engendered a mechanical and uninteresting surface, over which light plays with monotony, and hence that brilliant and scintillating effect so essentially the character of true mosaic is absent. This defect - and it is a grave one - is evident in the works in mosaic more or less recently set up in Paris, notably in the apse of the Pantheon, the east end of the Madeleine, and the vaulting of the great staircase of the Louvre. Those in the apse are finely designed, but scarcely look like mosaic, those in the Madeleine still less so, and the last not at all.

The artist who designs for this material must set aside all the principles he has learned to estimate in paint, either of oil or tempera. As an instance of a painter, pre-eminently delicate in his colour and tone, failing as a mosaic designer we may quote Cimabue, whose beautiful designs in the cathedral at Pisa would have been far more effective had the artist painted them upon the wall with the medium in the requirements of which he was so great a master. The same criticism may apply to the mosaics in recent years set up on the west front of Santa Maria del Fiore in Florence. The very first principles which go to make a fine picture are just those which should be avoided in mosaic - elaborate modelling, delicate transitions of light and shade and picturesque effects of dark and light, materialistic resemblance indeed. The designer for mosaic should ever bear in mind his material, and in his designs for it he should accentuate those characteristics which belong essentially and specifically to mosaic and to no other technique. If he is a painter, he must forget his lessons in that art and take up with new ones - those which teach broad masses of colour obtained in lines. He will find that effects gained by a technique employed in oil colour look bald and ridiculous when translated into mosaic. Watercolour and pastel are by far the best media for cartoons to be copied in mosaic. We do not know how these were executed in ancient days; probably the design was drawn on the wall, and there were no cartoons. The master not only invented, but he was the master-workman also, and that is how it should be. The probability is that the custom of drawing the design upon the wall practised by the early frescanti was the survival of a method adopted by the mosaicists, just as their method repeated that of Roman and Greek wall-painters. Of course this direct method leads to a large style, a style harmonizing with environment, scale, &c.; the tendency is to draw large in a large building, to draw small in a small one. Anyhow, this is quite certain, that all the fine Byzantine and 13th century mosaics, as well as wall paintings, were executed in situ and not away, as was the usual custom in England and elsewhere until recently.

Mr Harry Powell has permitted the writer to make use of some of his reflections upon the mosaicist's art in the following notes. The mosaicist should not separate the artistic from the technical details of his craft. He must study not only the decorative effect, form, colour and spacing of his design, but the surface to be covered as well as the materials with which he builds.

Surface

Good brick-work, the mortar joints slightly cut back, affords the best foundation for mosaic. The hollow and sharpedged joints provide a key for the cement into which the cubes will be set, and they diminish the risk of sagging, a not uncommon event if the cement is not welded to the wall by being well pressed into the joints. If the mosaic is to be applied on stone, the stone must be notched and well roughened to provide support. Whether the surface is brick or stone, it must be well saturated with boiled oil to prevent suction, because if too much suction takes place the powder only of the cement will remain and the cubes will drop out.

Cement

A cement suitable for mosaic is one which retains its tenacity, which can be applied in layers, which sets slowly, and which is not liable to change colour after long exposure. These conditions are best met by an oil cement. One consisting of equal weights of white oxide of zinc and carbonate of zinc, mixed with double boiled oil and containing small proportions of wax, gold size and slacked lime gives good results. This cement can either be white or red, white where greyness of tone is desirable, red where a richer effect is desirable. It is generally mixed with a small portion of oxide of iron or oxide of manganese, which prevents the whiteness of the joints from rendering adjacent tints grey from a distance.

Atmospheric Corrosion

As the atmosphere of modern towns is more corrosive than that of medieval Venice or medieval Rome, it is important that, in choosing the cement and the materials to be imbedded in it, the mosaicist should be certain that they are impervious to atmospheric impurities.

Glass

Although marble, mother of pearl, and other substances have been, and are still, occasionally used, the predominant material in ancient as well as modern mosaics is glass. When prepared with due regard to the continuing proportions of its ingredients, glass is impervious to the action of ordinary acids, and is practically indestructible. It can be made to assume almost every shade and tint of colour (see Glass). There are many kinds of glass, but for mosaic work either a potash-lead or a soda-lime glass is usually employed. Both of these glasses can be rendered opaque by mixing with the ingredients either oxide of tin or a mixture of felspar and fluorspar. Glass rendered opaque by the admixture of felspar and fluorspar has a bright, vitreous, easily cleaned surface, and readily develops brilliant colours.

Production of Colours. - Colours are obtained by mixing and melting with the ingredients of the opaque glass small proportions of certain metallic oxides. Oxide of chalk gives a purple blue; oxide of copper gives a peacock blue; oxide of copper with oxide of iron gives a green; oxide of copper mixed with oxide of iron and a strong reducing agent gives a red; oxide of chromium a green; oxide of nickel a purple; oxide of uranium a yellow; and oxide of manganese a violet - or a black if a larger quantity of oxide is used.

Manufacture of Glass Slabs

The mixtures, in a state of powder, are shovelled into crucibles standing round the grate of a furnace, and when fusion is complete the viscous glass can be coiled upon the heated end of an iron rod and removed for use, very much in the way that thick treacle may be coiled round the bowl of a spoon. A mass of molten glass, thus collected, is allowed to fall upon a flat iron table, and is pressed into a slab about 6 in. square and in. thick. The slabs are removed to an oven, where they are allowed to cool slowly, and when cool are removed and broken by a hammer or a miniature guillotine into tesserae or cubes The fractured edge of the tesserae is used for the surface of the mosaic.

Gold and Silver Slabs

The tesserae containing gold or silver leaf are as impervious to surface corrosions from the effects of atmosphere as the solid colours. The process of manufacturing a gold or silver slab for mosaic work is to spread the metallic leaf on a very thin tray of transparent glass, about 5 in. in diameter, and after it has been heated to press upon the surface of the leaf a mass of molten glass, so as to create cohesion between the molten glass and the glass tray through the pores of the metallic leaf. The slabs thus formed contain gold, silver or platinum leaf hermetically imprisoned between two layers of glass. The slabs are cut up into tesserae or cubes by means of a diamond or glass-cutter's wheel. Only one surface can be used for mosaic work.

Tinted Metals

By using coloured glass for the thin glass trays which form the surface of the metallic slabs a variety of tinted metallic effects are obtained. Moreover, if the glass which is to form the background is coloured, and if the slab after it has been cooled is strongly reheated, the leaf becomes sufficiently disintegrated to allow the colour of the background to show through, with the result that the colour effect of the metallic leaf is modified.

Palette and Tools

The palette of the mosaic worker is a shallow box with many partitions, each division containing differentcoloured tesserae. The only tools required are clippers, for shaping the tesserae, and a pointed awl for pricking through the cartoon into the cement the outlines of the design. Although the process and tools are simple, it requires prolonged training of mind, hand, eye and fingers to enable a workman to create in mosaic a living representation as distinguished from a lifeless copy of the master craftsman's design.

Drawing directly on the Wall. Curved Surfaces

If the mosaicist desires to draw his cartoon directly upon the wall, a necessary procedure where curved surfaces are presented, he goes to work in the following manner. He causes a model to be made to scale of a dome, semi-dome or spandrel and upon it he draws his design with a brush in strong red pigment, having previously squared up the whole surface to scale. This done, he causes the dome, semi-dome or spandrel to be covered over with thick brown paper. This being attached to the wall with white lead sufficient only to give temporary adhesion, the brown paper is squared up to the scale of the small sketch; each square being relatively numbered. The master then sets his pupils to work to draw mechanically and copy accurately from the small design on to the full-sized dome, semi-dome or spandrel. This done, the master follows on, correcting with charcoal or brush until the whole design is developed in strong outline. Having made a slightly coloured sketch, the master with the aid of his pupils proceeds to mix all the tints in water-colour, adding colla di pesce or fish glue, and a little honey to prevent cracking. He then applies every tint separately, keeping each distinct, and above all minding that the local colours of all half-tints are different from the colour of all shadows. This done, he dips his brush in black and draws all the outlines, the thickness of which depends upon the distance which will intervene between his work and the spectator; in order that the black may not appear cold from a distance, he will add to one side of the line, a red line, thicker or thinner than the black, according to the effect he wishes to produce. It is sometimes effective to add upon the other side of the black line a green line, so that the purple effect of the black and red shall be modified.

Colour

We now come to the great question of colour and how to obtain it simply, and so that from a distance a blurred and woolly effect is not obtained. There should be a marked and sharp definition between all tints; they should not be fused; they should look sharply defined, as the squares upon a chessboard, and appear crude and brutal. The work which looks least refined near at hand looks more finished at a distance. Red and blue lines alternately laid, either more red or more blue as the purple is intended to tend towards red or blue, make the best purple. Green is best made with yellow and blue lines, the masses being separated by red lines, and the shadows of green should be red or blue: if red, they should be outlined with blue; if blue, with red. Red should be treated flatly, shaded with a deeper red, which should be of a warmer tone than the lights. Blue should be shaded with blue or red; and it is well to mix green tesserae with the blue in the lights, and again green tesserae with the blue or red shades to modify crudity. Pure white should be very sparingly used: it expands greatly at a distance. The best white is that which is of the tone of Naples yellow. Whenever it is necessary to use pure white, either a yellow or pink line should be set on one side of it.

It is impossible to keep the flesh too simple. The local colour, i.e. a red orange, is the staple colour. Features should be drawn in strong red or burnt sienna, or a rich brown. The outlines of limbs or the contours of faces should be made first with a green line, a little darker than the local tints, then a red line darker still, then a black or brown line. White draperies are capable of being treated with endless variety. Their shadows may be green, red, blue, grey or yellow. If the white drapery is to take a neutral tone when seen from a distance, all these tints should be employed, because when mixed those positive colours appear neutral when seen from afar.

Gold drapery has a fine effect. Bright gold expands to four times the width of the line, so that the lines of gold should be thin. It may be that the gold drapery is to appear greenish; when that is desirable the folds should be drawn in green outlined with red. All deep shades should be treated with red and hot browns. As gold expands so considerably, a larger interval should be left between the tesserae than between any other colour, even white. Each tessera should have a thin space of the ground colour round it. The tesserae should never be jammed: it is that which causes so many modern mosaics to look like oil-cloth or chromo-lithographs.

The Finished Cartoon

The finished cartoon, having been coloured in lines, should look exactly like the finished mosaic as regards effect; and the master, in leaking his cartoon, should always bear in mind that he is designing for mosaic, and not making a finished picture. The cartoon, when complete, is taken off the wall and cut up in pieces. Each piece is then carefully traced. The space upon the wall corresponding to each section is then covered with cement, but only upon that portion of the space which can be ,worked in mosaic in a day. The mosaic worker then applies the portion of the tracing upon the wet cement, and with a sharp point he pricks through the paper upon the lines thereon drawn; on removing the tracing he will find indents within the surface of the cement, which give him his cue to all the forms. Setting up the coloured design by his side, he takes the tesserae, which exactly correspond in colour and tone with those on the drawing, and begins his work, commencing from the outline and working inwards towards the centre, the lightest portion being left to the last. Here comes in the real test whether the craftsman is capable or the reverse. This is soon judged by the master, who will put the work in and out until he is satisfied with the result. Unless the master has himself gone through the drudgery of laying the cubes he can be no teacher. He must be a craftsman as well as a designer, and must know by experience and practice in a very difficult craft what the material can do with ease and what it is not called upon to do by reason of its inherent limitations. If he has not so trained himself he is certain to pictorialize what he should conventionalize; and, moreover, he will set technical difficulties in the way which are impossible to overcome. He must aim at the greatest simplicity without dullness, at producing the greatest effect by the simplest means, and to do that he must know his material or fail. (W. B. RI.)