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One of the most recognized decorations of the pick-up technique is the millefiori glass, which has been commonly attributed to Venetian production. However, Portugal is the country where the largest known assemblage of this type of glass artefact has been studied and published. In this work, two important archeological contexts were selected: (1) Santa Clara-a-Velha monastery (SCV) and (2) São João de Tarouca monastery (SJT). The fragments selection was made based on the diversity of decorative motifs, colors, and original forms that has been associated with Portuguese production. The compositional characterization was conducted by performing micro-particle-induced X-ray emission (µ-PIXE) mapping, which facilitated the visualization of the distribution of different oxides across the different glass layers and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to obtain the major, minor, and trace elements composition, including rare earth elements (REEs) to determine which kind of raw materials were used. Additionally, µ-Raman spectroscopy was employed to investigate the opacifiers, while UV–Visible spectroscopy was used to study which chromophores are presented in the glass samples. All the analyzed glass layers can be considered to be of a soda–lime–silica type, and four different geological patterns (from GP1 to GP4) were detected and reported. This result can indicate that these objects were made by using silica sources taken from four different geological settings. Interestingly, the GP3 represents about 41% of the analyzed glass fragments and is compatible with the pattern detected in some production wastes found in two different archeological contexts located in Lisbon, which reinforces the veracity of the theory that this GP can be attributed to a Portuguese production. On the other hand, GP1 was probably attributed Granada provenance.

Little is known about the materials used in the manufacture of red window glass in the 19th and the first decade of the 20th century. Here, we have studied fragments from eight Spanish glasses from the 19th and 20th centuries. The red glasses consist of a single layer of red glass on a colourless glass substrate. The chemical composition, oxidation state, nature of colourants and crystalline precipitates were determined by a selection of microanalytical techniques. In the study, we have found that the red colour of the glass is due to the presence of Cu0 nanoparticles, the red glass layer has lower calcium content than the substrate glasses, which we found favours copper being present in the glass predominantly in Cu+. They also contain tin and iron while lead, described in historical and modern documentation, was absent. Tin must have been added to the glass as a Sn2+ compound and acted as a reducing agent for copper. Iron is also a well-known reducing agent, but does not act as such in the red glasses studied here. However, it may have facilitated the reduction of copper to Cu0 by promoting its incorporation into the glass as Cu+ rather than Cu2+. Resumen: Poco se sabe sobre los materiales utilizados en la fabricación de vidrios rojos planos en el siglo xix y primera década del xx, por ello se han estudiado ocho fragmentos españoles de la época. Todos ellos están formados por una sola capa de vidrio rojo sobre un sustrato de vidrio incoloro. La composición química, el estado de oxidación, la naturaleza de los colorantes y los precipitados cristalinos se han determinado mediante una selección de técnicas microanalíticas. Hemos encontrado que la capa de vidrio rojo contiene nanopartículas de Cu0, y que tiene un menor contenido de calcio menor que el vidrio sustrato, lo cual favorece que el cobre esté en el vidrio predominantemente como Cu+. Tal y como está descrito en la documentación histórica y moderna contienen estaño y hierro, pero no se ha verificado la presencia de plomo. El estaño se agregó al vidrio como un compuesto Sn2+ y actuó como agente reductor del cobre. El hierro a pesar de ser un agente reductor, no actúa como tal en los vidrios rojos estudiados. Sin embargo, su presencia podría facilitar la reducción del cobre a Cu0 al promover su incorporación al vidrio como Cu+ en lugar de Cu2+.