§ 2. MOSAIC.
The mosaics of figures exposed at the time of Fossati’s repairs are many of them figured by Salzenberg, although his harshly coloured diagrams can but very inadequately represent the beauty of the originals. We give here his descriptive text in a slightly condensed form as a basis for our own remarks. Dethier[374] asserts that only a part of the mosaics discovered were published by Salzenberg, and that Fossati preserved others inedited in his portfolios.[375]
The mosaics are formed of glass of various colours cut into small pieces and applied to the vaults with a cement. The gold mosaic was made by laying leaf gold on the glass, which was then covered by a thin film of glass to protect the surface. Silver mosaic was made in the same way. The gold was used, in spite of its apparent abundance, with great economy. For instance, in vertical spaces high up and only visible from almost immediately beneath, the tesserae are arranged in horizontal rows at a distance of two or three tesserae from each other with their upper edges projecting. The projecting edge of the lower row hides the bare space between it and the row above. There is thus a saving of more than half the material, and great play of light is obtained. The tympana of the aisles are covered in this way. The coloured tesserae are set in the usual way, as the difficulties involved by the other method in the curves of the ornament would outweigh the saving of material.
Besides gold and silver, red, blue, and green are the principal colours; though others are used in the heads of the figures. The vaulting throughout was covered with a background of gold, on which are conventional patterns that follow the forms of the construction. Some of the spaces have representations of figures.
In the bands of ornament are gamma-crosses [swastikas], hearts, leaves, and crosses, placed in circles, squares, and other figures. There are no sharp arrises to the vaults, but patterned bands are placed on the rounded edges.
The vault of the narthex has its wide transverse bands adorned with gamma-crosses. In the domed portions between the transverse arches are diagonal bands which culminate in a circle inclosing a cross.[376]
The vaults of the gynaeceum, perhaps because they were visible from the nave, are more elaborate than those of the aisles below.[377] Salzenberg’s Plate xxv. shows the western dome on the south side, on which is represented the descent of the Holy Spirit: the arches have the same ornament as those below.[378]
Details of the dome are given in Salzenberg’s Plate xxvi. The edges of the ribs and window openings are covered with bands of ornament. The faces of the ribs have alternate squares and crosses, which decrease in size as they get higher. The central space has lost its figure subject, but it is surrounded by a wide border.[379] The sides of the window openings are lined with silver mosaic. The lower part of the dome is not decorated, as the projecting cornice hides it from below.[380]
The edges of the exedra-conchs have bands similar to those on the great arches, and the same pattern occurs again on the edges of the eastern barrel vault, and the bema apse.[381] The rest of the decoration of the surface of the apses has disappeared.
Over the centre door from the narthex to the nave is represented Christ on a throne, holding a Gospel open at the words, “I am the Light of the world: Peace be with you.” A monarch is prostrate before him, and in medallions on either side are Mary the Intercessor, and Michael the Protector.[382]