SCIENTIFIC INVESTIGATIONS OF ANTIQUE LACQUERS FROM A 17TH‐CENTURY JAPANESE ORNAMENTAL CABINET

A recent restoration of a 17th‐century Japanese lacquer cabinet revealed various later treatments over the original black coating to maintain and preserve the high gloss of the oriental cabinet over the course of time and to meet changing tastes. The comprehensive investigation on a series of coating samples was executed by means of two hyphenated techniques: gas chromatography – mass spectrometry (GC–MS) and pyrolysis combined with GC–MS (Py‐GC–MS). The results showed that the original lacquer is based on urushi and linseed oil, while the past interventions are composed of sandarac, shellac and dammar. Additional microscopic studies proved the multi‐layer structure of the lacquer and the use of different pigments.     

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.     

CHARACTERIZATION OF RED‐COLOURED SLIPS (ALMAGRA) ON ISLAMIC CERAMICS IN MUSLIM SPAIN*

Small objects found in Islamic (eleventh‐century) kilns excavated in Zaragoza (Spain) were studied to determine the nature of the red coating of almagra pottery. Ceramics with almagra decoration were completely coated with a glossy deep‐red layer, a slip, applied to the body before firing. Chemical and mineralogical studies were carried out, together with analysis of a surface treatment with organic compounds. The results of this study confirm that almagra ceramics were produced by means of a specific and elaborate process (slip preparation, firing and wax application), demonstrating the introduction of this slip into local production during the Islamic period.     

ARCHAEOMETRIC INVESTIGATIONS OF SGRAFFITO CERAMIC TILES (FIFTEENTH‐SIXTEENTH CENTURIES) RECOVERED FROM EXCAVATIONS IN UDINE (NORTH‐EAST ITALY)*

Most of the Renaissance sgraffito tiles excavated in Udine (Italy) constitute a homogeous group, the tile body having a CaO/MgO molar ratio ?= 3:2. They were produced using a dolomite‐ and calcite‐containing clay fired at 900–950°C. A small group of samples, with a lower firing temperature and a CaO/MgO ratio ?= 2:3, was probably produced in a different factory. Slip and transparent glaze, characterized by optical microscopy and inductively coupled plasma atomic emission spectrometry, are an illite‐rich clay and a lead silicate, respectively.