New insights into 17th and 18th century glass from Portugal: Study and preservation

• Main Author: Coutinho, Inês Alexandra Ramalho
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2016
• Subjects: Art history
• ISBN: 9781083602114; 108360211X

Early Modern glass from the Iberian Peninsula has - so far - seldom been investigated. The project, combining chemical analysis with a stylistic approach, and focusing on composition and technology, aims to characterise glass objects circulating in the national territory, in an attempt to identify their origins and to eventually bring to light a Portuguese centre of glass production. The chemical composition of more than 200 glass fragments was determined by means of μ-PIXE down to a level of tens of μg/g. The results obtained allowed one to select some objects to further extend the analysis to the trace and rare earth elements (REE) down to the ng/g level, through the use of LA-ICP-MS. Glass colours and natural hues were studied by means of UV-Vis reflectance spectroscopy and, when necessary, enamels were studied by means of μ-EDXRF and μ- Raman microscopy. From all the objects analysed, it was possible to conclude that the great majority of the glass dating upto the 17th century, is of a soda-lime-silica type, which indicates a Mediterranean tradition. Venetian or façon-de-Venise shapes were identified, and for some of them a Venetian provenance was confirmed. For other façon-de-Venise shapes, the composition presented differences that led to the conclusion that new façon-de-Venise production centres could be recognised. From the only assemblage containing glass fragments dated to the medieval period, it was possible to attest the presence of Venetian glass in the Portuguese territory from at least the 14th century. Additional objects showed particular compositional features, such as high and very high alumina contents for instance, that, as far as it is known, do not match up with any of the known glass production centres in Europe. Allying the stylistic characteristics with the glass chemical composition, allowed one to identify some objects possibly belonging to a Portuguese production. Several glass fragments belonging to wine bottles were retrieved from archaeological excavations in Lisbon and were chemically characterised. The chemical analysis revealed an HLLA composition for all of them. For some of these fragments it was possible to propose an English provenance. Besides the chemical characterisation, a systematic analysis of the bottle shape was proposed since the shape can be an important factor in determining its chronology. A small percentage of the fragments were identified chemically as having mixed-alkali compositions, potassium-rich glass, and lead glass compositions. The latter two chemical formulations were found among the assemblages from Lisbon and the objects with these compositions were dated to the 18th century. These constitute evidence that Portugal followed European tendencies in their glass and its compositions. This is the first systematic chemical characterisation of Early Modern glass circulating in Portugal, providing new insights into trade between Portugal and its trade allies. As a part of the study, and to prolong the survival of these glass assemblages, simple and low cost optical sensors were developed for the in situ detection of the organic pollutant formic acid, which is emitted by materials usually used in storage and in the display of glass. The detection of the presence of this acid can play an important role in the preservation of this valuable heritage; glass.