Glass-Sensors: Assessment of Complex Corrosive Stresses in Conservation Research

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GLASS-SENSORS: ASSESSMENT OF COMPLEX CORROSIVE STRESSES IN CONSERVATION RESEARCH DIETER R. FUCHS, HANNELORE ROMICH, AND HELMUT SCHMIDT Fraunhofer-Institut for Silicatforschung (ISC), Neunerplatz 2, D-8700 Wdrzburg, FRG

ABSTRACT Glass sensors, based on K-Ca-silicate glass chips, with a low durability against corrosive stresses, offer a new method for assessing the complex environmental stress situation of monuments and pieces of art. The easy-tohandle technique is able to detect the combined impact of climatic stresses, pollution and microbiological effects as well as synergetic interactions. The chemical composition of the sensitive glasses enables judgements within few months. This way long-term estimates can be obtained without costly long-term investigations. The corrosion progress is determined by microscopy and IR-spectroscopy of the weathered glass sensor surfaces. The sensors are already operating in the field of stained glass window preservation. They monitor the efficiency of different kinds of external protective glazings and the remaining stresses from the in-door environment of cathedrals.

1. INTRODUCTION In conservation research the evaluation of the aggressivity/corrosivity of environments has a major key function from various points of view. Basic investigation of the interaction between the materials and the environmental stress at the very spot of a site or building structure can render detailed understanding of deterioration phenomena and corrosion mechanisms. The correlation between specific stress situations and resulting decay processes also may be essential for the design of adequate protective measures as well as for the tailoring of time-lapse laboratory tests for conservation materials and techniques. The assessment of the combined corrosive efficacy induced by climatic influences, pollution-related parameters as well as synergetic effects is of high interest for judgements concerning the protective features of already applied conservation concepts. In the field of stained glass window conservation the state-of-the-art is characterized by transferring analytical standard methods from the fields of climatology and environmental engineering into conservation research. Measurements of temperature, temperature gradients, air humidity, condensation effects, pollutant concentrations in air, precipitation, and run-off water, microbiological records - the spectra of relevant environmental parameters as well as the efforts of analyzing them can be extended at pleasure. But up to now the knowledge about the exact conclusions between these influences and the resulting impact on the material, as well as the synergetic effects among them is still fragmentary. The parameters are changing locally and with time permanently. Scientific investigations including model calculations and simulation tests would have to set up a detailed framework first, to justify extensive - and expensive - climate and pollution control at the sites. But even when such theoretical background can be realized, the technical effo