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Preservation made to order

Sensor monitors corrosion process that historical organs in churches and works of art in museums are submitted to

eduardo cesar Sensor detects substances released by the degradation of woodeduardo cesar

A baroque organ in the Catedral da Sé cathedral in the historical city of Mariana, State of Minas Gerais, was monitored for one year and four months by a sensor developed by researchers from the University of São Paulo/USP, as part of a project for the preservation of historical organs. The project, named Sensorgan, is funded by the European Community. The technique evaluates the influence of humidity, temperature and organic acid vapors released by wood during the corrosion process of the venting pipes. “Based on this monitoring, we were able to define, for example, at what time the cathedral’s windows and doors have to be opened and closed to help maintain the metal, so that it lasts for a longer period of time,” says organ player Elisa Freixo, curator of the organ in Mariana. The organ was manufactured by master organ builder Arp Schnitger in 1700 and is one of the best preserved organs found outside Europe.

“The monitor is a combination of temperature, relative humidity and luminosity sensors and a dosimeter based on a micro scale with a crystal quartz disc measuring 0.5 centimeters in diameter and  of 0.1 millimeter thick linked to two gold electrodes that register subtle weight changes in any material deposited on the surface of the quartz,” explains professor Andrea Cavicchioli, from USP’s School of Arts, Sciences and Humanities, which is participating in the European project. A thin layer of the investigated substance – lead oxide, in the case of organs – is deposited on the quartz disc in the form of a film with nanometric thickness. When the sensor is placed in the micro environment that houses the organ, it is able to measure the speed of the wear-and-tear process, because the disc registers weight changes as being corrosion of the metal.

eduardo cesar Organ pipes in São Paulo City’s Mosteiro de São Bento monasteryeduardo cesar

Prior to being used for the evaluation of historical organs, the quartz micro scale technique had already been used in environmental sensors for the monitoring of gases in the atmosphere. Cavicchioli, who is also a chemist, decided to adapt this methodology to monitor the response of painting materials in closed environments housing works of art, such as in museums and art galleries, based on the knowledge that the degradation process of substances such as paints, varnishes and glues occurs because of mass variations. “When a coat of varnish placed on the micro scales is attacked by environmental factors, it oxidizes, and undergoes an irreversible transformation, which increases the weight; this is registered by the micro scales,” he reports. The technique, which nowadays can be applied with the help of an automatic device developed by the team, evaluates the quality of the environment where the works of art are exposed, because it registers the atmosphere’s oxidation effects on the decomposition of organic materials used in paintings.

This work resulted in an invitation to participate in a European project, led by the Göteborg Organ Art Center, a Swedish institution dedicated to the conservation of the art of the organ. The objective of the project is to detect whether environmental conditions of the place that houses an organ can lead to its degradation or not. Seven partnering institutions are taking part in this project, including USP and the Swedish center. Other participants include researchers from London University, from Poland’s Catalyst and Surface Chemistry Institute, from Italy’s Institute of Climate and Atmosphere Sciences, from Poland’s Olkusz Municipal Culture Center, and from Sweden’s Chalmers Technology University. The research studies began in January 2006 and the monitoring techniques have been tested since then on European heritage organs and on the organ in Mariana.

The team from USP developed automatic prototypes to detect the action of gaseous substances inside the organ. These substances, mainly acetic acid and formic acid, are released by the degradation of wood. When combined with condensation phenomena, they create conditions that cause serious damage to the metal parts of organs. “Although it seems to be inert material, wood is the main enemy of lead pipes,” says Cavicchioli. Concurrently with the European program, he began a Jovem Pesquisador project, funded by FAPESP, to evaluate how the combination of different environmental factors leads to the degradation of varnish in works of art.

The Project
Impact of micro environment on the conservation of cultural heritage (nº 06/61437-3); Modality Apoio a Jovens Pesquisadores Program; Coordinator Andrea Cavicchioli – USP; Investment R$ 201.187,36 (FAPESP)