Development of a non-destructive test to assess the quality of new pieces of glass smalti from Murano (Italy) used in the “trencadís” cladding

During the restoration of the cladding of a heritage building it was noticed that some of the new glass smalti pieces from Murano used in the “trencadis” (typical Catalan modernism style mosaics) are deteriorating and cracking prematurely. In contrast, some of the original glass pieces put in position years ago seem to have only minor decay problems, even though they were produced in the same glass workshop in the area of Murano (Italy). Consequently, the private organisation that is responsible for the building decided to contact LiTA (Architectural Innovation and Technology Laboratory, a research group of the Universitat Politecnica de Catalunya) to collaborate in order to obtain better performance and similarity in the new parts of the cladding that are being built, as well as better results in the restoration of the original. A multidisciplinary research team was then created with a holistic approach to cover all aspects involved. The main goals of the research were: ? To measure and assess the quality of the materials used in the cladding. ? To assess and improve as much as possible the production of the materials to achieve better quality. ? To assess and improve as much as possible the building processes and practices associated with the cladding. ? To study the interaction between the materials under the building situations that were categorized. In this context, it is particularly important to evaluate the mechanical characteristics of the Murano smalti glass to avoid the appearance of unwanted cracks and fissures on the material. Murano smalti glass is now produced in small round (diameter O 30cm) and rectangular (20x40cm approximately) shapes, following traditional procedures and controlled by artisanal means. Given that every glass piece is quite different from the others, a fast, cheap and portable method needed to be developed to assess the quality of each piece before shipping to the building site. We conducted several studies to determine the modulus of elasticity (MOE) of each piece, by making it vibrate by means of an impulse and analysing the natural frequencies of vibration. The method proved fast and effective for regular shapes. We obtained promising results with round-shaped pieces and we are now investigating other more irregular shapes.