Brass lamps: Preliminary study on the constituent materials and production technology by X-ray and microscopical techniques

This paper reports a preliminary study concerning two brass lamps belonging to the Évora Museum collection and one brass lamp belonging to a private collection. The main objective of this study was to acquire scientific data to assess the production technology used in the making of these lamps. Optical microscopy, X-ray digital radiography and scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) were used to study the base, oil reservoir and the reflector of the selected lamps. SEM/EDS analysis showed that although the analyzed parts of the lamps have slightly different elemental compositions, they are all made out of yellow brass (Cu 70% and Zn 30%, in w.t.) and soft-solder (Pb-Sn alloy). The lamp bases alloys also contain tin, which increases the dezincification resistance, and lead was also found in one of the lamps, which is known to increase malleability and reduce the melting point of the alloy. Metallographic procedures were performed on two selected components of a lamp. Observation of as-cast and wrought brass microstructures support the main processing techniques used in manufacturing of this kind of objects. Likewise, the metallic phase encountered - alpha - of the Cu-Zn binary system - are in agreement with the elemental analysis performed. This study reveals the importance of the radiography analysis to obtain a better understanding of structural aspects, as much thickness and density as mechanical processes and their impact on the manufacture of the different elements of these lamps. Fissures, cracks and restoration marks could also be identified in these lamps.