In the quest for historical Lisbon through 17th century Millefiori glass

Abstract

Being Lisbon one of the world’s most important trading port and a place where historical documents attest the presence of at least four glass furnaces working between the 16th and 17th centuries, the authors decided to investigate one of the most luxurious coeval glass decorative techniques (millefiori) found in Lisbon to try to understand the trade route and raw-materials provenance of these artefacts.For this work, two Lisbon archaeological contexts were selected: Largo do Chafariz de Dentro (LCD) and Santana Convent (LCS) due to their significant amount of interesting millefiori fragments (eight fragments) and the presence of production waste (one in LCD and three in LCS). The analysis, comparison and discussion of glass production waste (PW) and archaeological glass artefacts will be carried out for the first time.For this work, macroscopic and microscopic observations were combined with the chemical characterization of colourless and coloured glass to make the morphological characterization and to determine which raw materials were employed in its production. The chemical characterization was made by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to obtain the major, minor and trace elements composition, including rare earth elements (REE).The chemical composition of the selected samples revealed that all the millefiori glasses are of soda-lime-silica type (part of them made with Levantine ashes and the other part with barilla) while the glass type of PW is was not attributed.Regarding the Lisbon millefiori glass fragments, there is a notable relation between the concentration of major components associated with the silica source, namely SiO2, Al2O3 and TiO2. Moreover, upon analysing the geochemical patterns exhibited by the production waste found in LCS context and comparing it with the pick-up glass fragments, a consistent trend emerges, implying that both were made by using either the identical silica source or, at the very least, a closely related silica source. For this reason, the possibility of a Portuguese local production may be proposed, especially when some decorative patterns are clearly from Portuguese inspiration (e.g. caravel and cross of Christ), while the authors admit that more data analysis is still required to prove this hypothesis.