Tüskés Anna (szerk.): Omnis creatura significans - Tanulmányok Prokopp Mária 70. születésnapjára (2009)

Antik és középkori művészet

Essays in Honour of Mária Prokopp

of 660 pounds of tesserae in various colors and shades.^ Since we know that glass tesserae were also being produced at the time in Orvieto itself, can it be that it was only the hue of the Venetian tesserae that mattered? Is it possible that the more stable nature of the Venetian soda glass was a factor as well?

A very rough calculation of how much 660 lbs of glass tesserae would make in terms of a mosaic surface-turns out to be about 12 square metres or about 10% of the Orvieto fagade mosaic.20 So far, no soda glass tesserae have been identified among the ruined remains of the Orvieto mosaics (Fig. 5) but this may be due to lack of analysed samples.21 In any case, the late Trecento documents tell us that the fagade mosaics there made by Orcagna and others were defective because they were badly set and discolored. Hardly were the individual scenes finished than repairs and restorations ensued.22 For a complete study of their complicated history, see the recent article by Giulio Manieri Elia and Paul Tucker.23

What kinds of glass were used elsewhere in Italy for 13th and 14th century fagade mosaics? The fact is we don’t know and this goes for Lucca and Florence as well as for Rome.

As for interior mosaics during the same period of time: soda glass and natron do turn up in the late 13th century mosaics at Santa Maria in Trastevere.24 Were these tesserae manufactured then, or could they be spoils—recycled from other sites? In Florence, potas- sic glass was used for the early 14th century mosaics in the Baptistry’s gallery.25 If potassic glass was used throughout the Baptistry vault, this would partly explain its poor condition and the many heavy restorations it has endured.

What is known of another essential ingredient in glass tesserae—the silica? What came from river sand and what came from quartz bearing pebbles? Can one deduce from what rivers or mountains this material may have come from? Silica from sand tends to be less pure than from pebbles and would have required different preparations.

And what of the metal oxides used for the coloring? Is it possible to distinguish between I4th-century tesserae and later ones inevitably introduced to replace the losses?

Returning to Prague. What about the plaster used? Luigi Solerti, a Venetian mosaicist, who was in Prague in 1879, distinguished a layer of lime and crushed brick as well as another vaguely indicated as an area of lime and marble dust.26 Both types of plaster were conventional. Matejcek writing in 1915 mentions two layers of plaster.27 This brings us to the matter of earlier restoration campaigns. There may have been one in 1478.28 A fire occurred in 1541 with unknown consequences for the mosaics

.29 It has been said that the mosaic was whitewashed in 1619.3° Matejcek mentions restorations before 1832 and 1837 but no documentation for these is known to me.31 Later on in the century, the mosaics were deliberately abraided to get

rid of the whitish deposits ascribed to oxidation—an operation which must have further weakened the condition of the tesserae.32 in 1857 and 1890 pieces of the upper border fell down. Soon afterwards, in 1890 it was decided to detatch the entire mosaic and repair it.33 Twenty years later in 1910, the mosaic was returned to its original site.

The frequency of restorations throughout the 19th and early 20th centuries occurred when Prague was still part of the Austro-Hungarian empire. Moreover, this coincided with a general revival of interest in mosaic manufacture all over Europe. There is the Albert Memorial in London, mosaic schools were founded in Paris, Munich and Innsbruck.34 Between 1836 and 1845 mosaics were stripped from the walls of churches in Murano, and Ravenna and then sent to Potsdam and Berlin.35 Wittelsbach castles were adorned with new mosaics. Luigi Solerti, the Venetian mosaicist, who consulted on the Prague mosaic between 1879 and 1890 was also involved with the mosaic schools in Innsbruck and Munich.36 Could it be that the work done on the St. Vitus mosaic was part of a widespread mosaic revival? Would it be possible to recognize the hands of the various restorers involved by a study of Solerti’s and other mosaicists’ work elsewhere? An- dreescu was able to pick out the work of Moro and Salviati in areas of the Torcello mosaic.37 Moreover, scientific means exist today for distinguishing between old and new tesserae.38

Now to the big question: in view of the nature of the Prague mosaic with its potassic tesserae, its exposure, its frequent restorations, how much can really remain of the i4th-century mosaic? Italian fagade mosaics such as Santa Maria Maggiore in Rome and Orvieto Cathedral have been re-worked many times over. Could the Prague mosaic have escaped similar treatment? Throughout the mosaic there are notable inconsistencies in the setting of the tesserae. More than forty years ago, Karl Hettes noticed that a number of the St. Vitus tesserae had a bevelled wedge shape known in Italy as tessere a cuneo.39 The only other examples known to me of this type date from the 5th century at Galla Piacidia in Ravenna.4° Could these Prague tesserae be spoils? Other instances of recycled tesserae are well known going back to Carolingian times: at Aachen and in Rome at Santo Stefano Ro- tondo, Sant Prassede and San Clemente.41

Hettes also noted another interesting feature in the Prague mosaic: the different color of the support glass for the metallic tesserae (Fig. 6). Red predominates in the central panel giving the main scene a warmer glow while dark green and blue were used for the flanking mosaics.42 It is known that red glass without lead in it is not ideal for the adherence of metal foil (does the Prague mosaic have lead in its red support tesserae?). Green and blue glass are better in this respect.43 In fact, this is mentioned in a I5th-century mosaic treatise published by Milanesi in the 19th century.44 Were the Prague mosaicists aware of this? Another question:

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