Susana Coentro

First archaeometric study on medieval glass found in Beja (Southern Portugal)

ABSTRACT During an archaeological intervention that took place in Beja (southern Portugal), at Avenida Miguel Fernandes, between August 2003 and March 2004, a set of 137 silos was discovered. The excavation yielded an assemblage of glass that can be dated between the fourteenth and the seventeenth centuries. For this investigation only the fragments from the medieval contexts were considered in order to provide an overview of the use of glass vessels in a Portuguese town in the fourteenth and fifteenth centuries. A group of eleven medieval glass fragments was chemically characterised by means of µ-PIXE (particle-induced X-ray emission) and UV-vis reflectance spectroscopy. Analysis by µ-PIXE enabled the determination of the chemical composition, and UV-vis reflectance spectroscopy was used as a complementary technique to identify the metallic elements responsible for different colours observed in the glasses. Results showed that the analysed objects are in the majority made of a soda-lime silica glass, indicating a connection with the Mediterranean tradition. Cobalt and copper were the colorants used to obtain the blue and turquoise glasses, respectively, whereas iron is responsible for the green and yellow colours.

The Cistercian glazed tiles of the Monastery of Alcobaça: characterization of the colour palette

ABSTRACT The glazed tiles that paved the apse of the Monastery of St. Mary of Alcobaça were a rare decorative element in the most important part of this Cistercian construction. These medieval tiles, all monochromatic, are believed to be a thirteenth-century production and represent some of the first examples of tin-opacified glazed tiles in Christian Portugal. Although lead glazes have been extensively used in medieval pavements in North-Western Europe, opaque tin-glazes are far scarcer. The technology used in this case is a testimony of mixing cultures, combining Cistercian Order traditions of building materials and techniques with the Islamic tin-glazing technology brought to the Iberian Peninsula in the tenth century. These glazes were applied on tiles of several geometric shapes to achieve the final decorative effect. For the first time, these tiles were analytically characterized to determine the chemical composition of the different colours of glaze and these differences were assessed to explain the variety of colours and shades observed. The analytical techniques used were µ-PIXE (micro-particle-induced X-ray emission), µ-Raman spectroscopy and optical microscopy. Samples selected for this study comprise all colours observed in Alcobaça tiles: white, turquoise, brown and several shades of green. Results show that the variety of colours and shades are consistent with different proportions of CuO, Fe2O3 and SnO2 in a lead-glazed matrix, together with a K-feldspar-rich white inner layer, most likely to be a slip.