THE TECHNIQUE OF GLASS MOSAIC

“Either light is born here, or, confined here, rules freely. Perhaps it is the earlier light, whence comes now beauty of the sky.”
titulus in church St. Andrew the Apostle at Ravenna

Angela van der Burght

The technique of making glass mosaics -as one of the processing techniques- developed independently of the technique for mosaic glass -which belongs to the originating techniques- in which small, pre-formed stones are used in fusing and overplayed work, such as cased glass. It is not known when the first mosaics were made, but so much is certain that the word ‘musivum’ was used for the first time by Aelius Spartianus. The most obvious etymological explanation for the word mosaic is that it derives from the word 'muse', because Themis' daughters -the Muses- have been represented frequently in this technique. The oldest known mosaics are still related to running water, in Pompeii for example, water basins, fountains, baths and walls are covered with mosaics of little stones and shells whose extra twinkle comes from light on water cascading over these mosaics.

The origin of the inlay technique can be found with the Sumerians and the Assyrians, who were already familiar with encrustation in 3.000 BC. They covered the walls of the palace of Warka in Chaldea, with tiny, bright-coloured, enameled terra cotta cones, which were set into the wet clay or plaster on their pointed ends. The Egyptians made inlay works for decorationing sarcophaguses, furniture and hieroglyph. Figure pieces or emblematics, a part of a mosaic laid in a larger mosaic, arose probably in Greece where in 1930 the pavement of a temple was discovered at Olynthus, dated from 347 BC. The mosaic figure was fabricated with white gravel on a black background or fond. At Antioch, Pergamum and Alexandria, different types of marbles and precious minerals were used for the decoration of building and floor decoration. In the large Hellenistic cultural centres mosaics reached their utmost technical perfection. Sosus, who worked in Pergamum, in the third century B.C., was considered the best mosaic artist of the antiquity by Plinius. Sosus was the maker of the two themes that soon were copied on a large scale, namely the ‘drinking pigeons’ and the ‘unswept floor’.

Roman military expeditions, in Asia and Egypt brought back to Italy, the idea of floor mosaic that extended the use of wall mosaics from Rome to Ravenna, in the fourth and sixth centuries. In imperial residences, public buildings and private houses mosaic floors were increasingly fashionable. Walls, columns and niches were very often covered by small pieces of stone, enamel ceramics, shells and little glass bits. From Sueton we learn that Caesar carried mosaics with him, spreading the technique throughout the rest of Europe. Opus musivum was the term for wall and floor mosaics, in which symmetrically placed, thinly cut fragments of coloured marbles or minerals were used. Later this was called opus sectile. The opus signinum, named after Signia, a place in Latium, was made of red earth. This kind of cheap pavement, a mixture of pounded bricks and lime, has often been used at Pompeii. Splinters of marble, porphyry and scattered gravel were added for decoration. The plainest mosaic tile form was the opus tesselatum, in which simple graphic cube forms were used for making geometric patterns. Emblemata were small parts, manufactured in a studio, ready made, then laid into a floor or wall. For wall mosaics primarily glass was used, delivered by glass factories, then cut by the mosaic makers themselves, in little squares of 1x1 centimeters tesserae. The broken flanks were put in visibly tilted frontward, into the plaster, expressly to catch the light and letting the surface sparkle. Even in the opus vermiculatum, resembling swarming worms, little glass pieces were used. The first Christian wall mosaic was made at Rome, in 390. In the Byzantine Polyeuktes church in Constantinople, in the year 525, for the first time tiny gold coloured stones were laid in so distortedly that it created a twinkling sensation intensified by light reflectioned from every angle. Until the late Middle Ages mosaics were made on the spot (in situ), later in sections, in studios. The pieces for glass mosaics were cut with a chisel out of opaque coloured pizzas, flattened by a lump of hot glass on an iron plate or marver. Gold (aurum massivum) and little silver stones were acquired by pasting albumen with gold and silver leaf on clear or transparent pizzas, and by igniting gold powder or placing gold leaf between two layers. In the thirteenth century gold leaf was replaced by the cheaper tin-bisulphide and in the nineteenth century by bronze powder. Mosaic studios nowadays cut the pizzas with mechanical chisel machines and selling the selected stones per kilo or per piece. These pieces are laid in a synthetic resin or assembling lutes with water-resistant cement. Glass mosaic pieces for sanitary ware are now imported from Italy and Spain, pressed from recycled glass.

In mosaics, decoration joins function: in walls and floors, normally exposed to moisture, water or in houses, whose interior and exterior is exposed, mosaics are functional and easy to maintain or clean. The surface to be decorated first was carefully leveled, then smeared with a mixture of lime and water. When the surface dried, then it was covered by a layer of plaster as thick as the glass pieces. Every piece was laid in according to the pattern and a contour line indicated where the plaster had to be cut out for each stone. With a refined paste or bitumen (a kind of natural asphalt) the stones were then put into the little holes. The joints were filled up, were all polished with sand stone or tin oxide. The glass for mosaic walls, niches and fountains came from Egypt until the late Emperial Age. As well, stone mosaics were made with glass when colour variations in marble or precious stones were not available.

Mosaics are laid in directly with the right side up, stone by stone in plaster, or inverted (transfer technique) and later fixed on their place with glued paper. In the inverted method (mosaico rivoltura) the stones are put with the right side in a temporary plaster (German: Setzteig), in real or plastic clay, or in damp sand. Then the stones are taken up with glued jute or adhesive foil to finalize their place and form. When the plaster has dried, the foil is removed or the glue dissolved in water to remove the textile. For incidental wall mosaics, the outline of the mosaic segment will be drawn, and then cut out, to fit into the pattern. Then, the mosaic can be laid in at the same level or laid upon it to be joined later. Artists work directly in the spot where stones are placed straight into the fresh plaster or on ready-made plates that can be fastened onto or in a wall.

Splendid eleventh century examples can be admired in the cathedral of Torcello, a minuscule island in Venice’s lagoon. The cathedral’s floors are carpeted with vividly coloured marble mosaics, as the walls, apse and chapels are draped with glass mosaics. As well, the Venetian basilica of San Marco has splendid mosaics. However, the most beautiful glass stones still come from Murano where a dazzling multitude of choices exists in various opaque colours with copious gold, bronze and silver variants.

In all different periods of art-history, glass mosaics have been used for decoration. In particular, monumentalists, at the beginning of the twentieth century, used this technique alongside stained glass, carpets and specially crafted furniture. There is still to be admired the mosaics of well-known plastic artists such as Gustav Klimt, Fernand Léger, Marc Chagall or Oskar Kokoschka. Antoni Gaudi brought the connection between architecture and technique to a summit. In his Krypta Colònia Güel, built from 1898 to 1917 south of Barcelona, patterns of masonry, stained glass windows and mosaics flow together seamlessly. In northwest of Barcelona, the Güel Park, exemplifies the flow of wall-, floor- and roof covered with every conceivable kind of ceramic and glass mosaic. Inside-to outside organic shapes flow and spill over into each other; reptiles, columns, stairs and pavilions are at once decorative/symbolic and functional shapes.

When you really pay attention you see mosaics everywhere: in the glass museum in Düsseldorf at the Ehrenhof you can see gorgeous 5x10 meter high mosaics of Anton Prikker from 1930. Monumental, as well as, refined in its detail are the walls 'Tag & Nacht' (Day & Night), pure abstract works with shapes in rhythmic shapes and linear order, its lustrous gold is the prime player. Or, the works of Niki de Saint Phalle, for example, her Il Parco dei Tarocchi at Garavicchio, Italy, that depicts the 22 Great Arcana from the Tarot, as huge sculpture-buildings. Already from a distance, the silver towers twinkle, beckoning visitors to enter into a womanly figure that contains the artist’s house and studio. Similarly, the works of Jan-Willem van Zijst for the An-Nur mosque at Waalwijk, the Netherlands offer a modern treat. In 1990, Van Zijst made a transparent glass mosaic four and a half meters wide for the large men's prayer room. On a base of float glass, are thousands of tiny lustre cathedral-glass stones. The text has been stained with a sea-green luster. This craft technique was chosen because Islam, historically, is not associated with an autonomous art. All art forms are craft or applied techniques: only Allah creates while humans merely count and measure. Mosaic techniques are used in mosques all over the world because with their square little blocks and geometries, mosaics are extremely suitable for counting and measuring. And, it must be said that laying in thousands of small stones certainly generates a humble feeling. An artist entirely cognisant of this was Irene van Vlijmen, who lived in Spain and sometimes works for years on her orders. At the beginning of this year she often works years on a single commission. At the beginning of 2000, Van Vlijmen worked in the Grand Hotel Karel V, in Utrecht. Here, she made wall mosaics for an entrance hall, a restaurant, ceiling paintings and tapestries. Her palette’s hues are Venetian mosaic stones of 260 colours with 20 gold variants.
In Van Vlijmen’s work even little stone became a monument.
©Angela van der Burght, 2000 for This Side Up!