How Byzantine Mosaics Are Made: Ancient Techniques Explained

In mosaic terminology, 'substrate' refers to the base material you are sticking your mosaic onto, such as wood, cement-based marmox, glass, metal, or plastic. 'Tesserae' refers to the mosaic pieces themselves, which can include glass, stained glass, ceramic tile, glazed tile, natural materials like marble, shells, wood, or mirror. Understanding these terms helps in selecting the appropriate adhesive for your specific materials.

A tessera (or tesoro) is any material used to create a mosaic that is attached to a substrate. This includes glass pieces, tiles, and even unconventional materials like Barbie dolls. The term refers to the individual pieces that form the mosaic artwork when arranged and adhered to a backing surface.

Glass-on-glass mosaic (GOG) is a type of mosaic where both the substrate and tesserae are made of glass. The substrate serves as the base surface, while the tesserae are the individual pieces that create the design. Common materials for tesserae include vitreous glass, glass beads, glass tile, milly fiori, small tiles, and stained glass. This technique is particularly popular when the goal is to allow light to pass through the finished mosaic.

Mosaic art is a decorative art form that creates images from small pieces arranged together to form a unified whole. The small pieces, called tesserae, are typically flat and square-shaped materials such as colored glass, stone, tile, mirror, or glass. From a distance, the image appears complete, but up close, the individual small pieces are visible.

Mosaic is an art form where small pieces of material work together to create an image or impression. From a distance, mosaic appears as a painting, but upon closer inspection, it reveals thousands of small individual pieces called tesserae. These tesserae have no meaning on their own; they only gain meaning when placed in proximity and relation with other pieces, functioning together as a whole image.

Smalti is colored glass produced by melting and coloring glass in its mass, then casting it into thin or thicker plates by Italians, who called them 'pizze.' These plates are then cut into rectangular tesserae. Gold has always been popular in mosaic, especially during wealthy empires like Byzantium, which incorporated large amounts of gold into their mosaics. The combination of colored glass and gold created the luminous effects characteristic of Byzantine religious art.

Smalt production has evolved through multiple technological stages: from small furnaces for melting glass tiles, to sintering, traditional boiling, and now to modern V4 technology. The manufacturing process involves grinding glass cullet, sieving to remove inclusions, mixing with pigments and fluxes, pressing tiles under 20 tons of pressure, and creating artistic variations by intentionally imperfectly mixing colors. JSG smalt represents an innovation, sandwiching smalt between glass layers to provide a glossy, durable surface at lower cost than traditional glass tiles. The palette development began chaotically during the Savva Serbsky project and evolved into systematic color stretching, resulting in over 1,000 colors currently available.

Smalti is not simply colored opaque glass in the form of cubes or plates used for making mosaics; it is a product of hand production. Glass powder with added pigments is fired at temperatures around 1000 degrees. Known since ancient times, smalti is rare and expensive but always in demand and often made to order. Over time, entire factories for its production appeared in the USSR. Smalti is not only resistant to abrasive substances, household chemicals, and humidity, but also to temperature fluctuations. It is much stronger than glass mosaic, allowing it to be used for external walls, pools, and other surfaces subjected to intense environmental influence.

The smalti from which the mosaics were laid is not merely colored glass. It is a specially manufactured material in which color and transparency are achieved by adding various metal oxides. Copper gave green and blue colors, cobalt gave blue, manganese gave purple. Golden smalti was made by baking a thin sheet of gold between two layers of glass, giving that unique golden brilliance that does not fade or darken over time. The golden mosaics of Kiev Sophia shine today as they did a thousand years ago. Each piece of smalti was inserted into wet plaster at a specific angle. This angle was calculated so that light would reflect from it in the right direction, so that the mosaic would glow rather than merely reflect light. This required incredible precision, incredible patience. One square meter of mosaic could contain tens of thousands of pieces of smalti, each of which had to be inserted by hand at the correct angle, in the correct place. This was work that required months, that required skill unattainable without years of practice.

The cathedral's mosaics use smalti, which is colored glass. The most expensive type is gold smalti, which contains thin sheets of real gilded silver in its composition. This explains its high cost and exceptional value. The cathedral also features 'stretched smalti,' created by pulling glass from a continuous mass into thin strips, then cutting them into small pieces for vertical mosaic placement.

Early Christian architecture emerged by adapting the Roman basilica form—originally used for law courts and public gatherings—into sacred spaces that expressed Christian beliefs through symbolic spatial arrangements, including longitudinal plans oriented toward the East (symbolizing Christ's return), cruciform layouts representing Christ's sacrifice, and richly decorated interiors using mosaics and frescoes to convey theological concepts to largely illiterate congregations, creating an immersive spiritual experience that influenced Western church architecture for centuries.

Santa Maria Maggiore represents the oldest Marian church in the Western world, founded by Pope Liberius in the 4th century on the site of a pagan temple dedicated to Juno. Early Christians strategically built churches on pagan sites, incorporating pagan elements like columns into Christian spaces. The Christian basilica adapted Roman architectural forms but made crucial modifications, replacing heavy barrel vaults with lightweight wooden beams to create spiritual lightness. The 5th-century mosaics represent the largest surviving early Christian mosaic ensemble, designed as 'Biblia pauperum'—visual scripture for illiterate believers—using typology to connect Old and New Testament narratives.

Since most ancient Christians were illiterate and could not read sacred texts, and only the wealthy could afford personal copies of scripture, biblical knowledge was primarily transmitted through oral hearing during worship services. Wall paintings in catacombs served as visual reminders of the biblical stories heard during services, functioning as a 'visual Bible' for the illiterate majority of early Christians. The fish (ichthys) was one of the earliest Christian symbols, serving as an abbreviation for 'Iesous Christos Theou Yios Soter' (Jesus Christ, Son of God, Savior). The anchor was one of the earliest symbols of the Eucharist, instantly recognizable to Christians while appearing as mere graffiti to non-Christians. The Good Shepherd, depicting Christ as a young man carrying a lamb on his shoulders, was based on Gospel narratives and was later removed from Christian art following the Sixth and Seventh Ecumenical Councils.

Santa Maria Maggiore, one of Rome's four major papal basilicas, was founded in the 4th century following a miraculous snowfall on August 5th that outlined the shape of a church on the Esquiline Hill, as witnessed by Pope Liberius; this basilica exemplifies the fusion of architectural styles from early Christian, Renaissance, and Baroque periods, housing fifth-century biblical mosaics that served as visual scripture for an illiterate faithful, along with Renaissance artworks by masters like Pietro Cavallini and Giovanni Battista Salvi da Sassoferrato, and precious relics including the crib of Christ and a portion of the True Cross that have drawn pilgrims for centuries.

Early Christian basilicas like Santa Sabina continued the Roman Basilica type with large central nave directing attention to the apse platform where priests conducted mass. The interior was lavishly decorated with colored marble and golden mosaics, while exteriors remained austere. The nave was twice the width of aisles (1:2 ratio). The flat entablature with Ionic columns created visual hierarchy. The mosaics formed a type of military Roman triumph, celebrating the triumph of the church with Christ as new Emperor. The wooden doors showed Christ crucified with thieves, symbolizing that through Christ and the church doors, salvation is gained.