A STUDY OF GLASS TESSERAE FROM MOSAICS IN THE MONASTERIES OF DAPHNI AND HOSIOS LOUKAS (GREECE)

In this work 51 glass mosaic tesserae from decorations of the two Greek monasteries of Daphni and Hosios Loukas were analysed by inductively coupled plasma optical emission spectroscopy, electron microprobe analysis and X‐ray powder diffraction. On the basis of the chemical analyses, after discrimination between the tesserae of the original decorations and those from other periods, it was possible to outline the distinctive traits of Byzantine mosaic tesserae. In both the monasteries, the original mosaics were decorated with tesserae produced with plant ash based glass, either of the typical composition or a mixture with natron type glass. The samples from the Hosios Loukas decorations show a more homogeneous composition compared with those from Daphni. The major differences among the original samples are due to the presence of opacifiers and colourants.     

MATERIAL CHARACTERIZATION OF CERAMIC TILE MOSAIC FROM TWO 17TH‐CENTURY ISLAMIC MONUMENTS IN NORTHERN INDIA

Coloured tiles from two northern Indian monuments were analysed for their body and glaze composition. The results suggest that three different groups of tiles were used, all comprising a stonepaste body with alkali glaze. One group has strong similarities to a major Indian glass group, known as high alumina mineral natron glass, while the other two are similar to Western and Central Asian plant ash glazes, although with much lower lime content. The colorants conform with those usually employed in pre‐modern glazes, with lead‐tin yellow Type I and Type II for opaque yellow, copper blue‐turquoise, cobalt blue, manganese purple, and green through mixing of lead‐tin yellow and copper blue.     

The Effects of Time,Restoration and Conservation Approaches on Twelfth-Century Cosmati Pavements

Abstract

This paper compares the current condition and appearance of Cosmati floors in six churches in Rome. Based on the assumption that all of the floors had a similar appearance when constructed, it is possible to see how the floors now reflect the original design and materials, the church environment, management decisions, restoration and conservation approaches. This illustrates the importance of considering all the significant features and possible outcomes of both a series of small interventions and major interventions. Many findings will also be applicable to other floors and mosaics.     

CHEMICAL CHARACTERIZATION OF ANCIENT MESOAMERICAN ‘COPAL’ RESINS: PRELIMINARY RESULTS*

So‐called ‘copal’ resins from nine Aztec/Mixtec turquoise mosaics have been subject to analysis by gas chromatography – mass spectrometry to examine their higher terpenoid composition with a view to botanical identification. Botanical specimens and modern commercial ‘copal’ resins were analysed for reference. A range of botanical sources for the resins was identified, including pine, Protium and possibly Bursera. The data reinforce the ambiguity in the use of the term ‘copal’ and demonstrate the need for further work on characterization of ancient Bursera resins.     

Electron paramagnetic resonance of mosaic glasses from the Mediterranean area*

Ancient mosaic glass tesserae sampled from archaeological sites located in the Mediterranean area have been analysed by Inductively Coupled Plasma‐Optical Emission Spectroscopy (ICP‐OES). The aim of the research was to understand the role played by 3d transition metals in the optical properties of such samples. In order to better identify the specific effect of the main chromophorous element, modern samples have been prepared in the laboratory by adding to a colourless base frit controlled concentrations of colouring oxides. Samples with compositional and optical properties similar to the ancient ones have been obtained. For all these modern samples, as well as for all the ancient ones, electron paramagnetic resonance (EPR) measurements have been performed. The features of the EPR spectra could be successfully associated with the presence and abundance of the paramagnetic colouring ions (namely iron, manganese and copper) and to their oxidation states. This could be a basic step towards understanding the provenance and chronological attribution of mosaic glass tesserae.     

MOSAIC GLASS FROM ST PETER'S,ROME: MANUFACTURING TECHNIQUES AND RAW MATERIALS EMPLOYED IN LATE 16TH‐CENTURY ITALIAN OPAQUE GLASS

A recent restoration of late 16th‐century mosaics in one of the vaults beneath the dome of St Peter's Basilica in Rome allowed sampling and analysis of a group of glass tesserae. The aim of this work is the characterization of opaque coloured glasses possibly produced in Rome. The characteristics of the glass from St Peter's were compared with those of Venetian and Tuscan production, in order to assess possible common origins. Chemical analysis of 30 samples was carried out by electron microprobe, while the nature and morphology of opacifiers were determined by X‐ray diffraction and scanning electron microscopy. Almost all the opaque samples were characterized by the presence of SnO₂ crystals. In addition, depending on the colour of the glass, other crystalline phases were identified: lead‐tin oxide (PbSnO₃) in yellow glass, cuprite (Cu₂O) in orange glass and two calcium‐tin silicates with different stoichiometry (CaSnSiO₅ and Ca₃SnSi₂O₉) in the green‐yellow variety. A frame of reference for identifying raw materials and glass‐making techniques is provided by textual sources, here examined in comparison with the compositional characteristics of the tesserae from St Peter's.