Combined imaging technologies make changes at the stone surface of cathedrals visible

Analysis of a stone surface with the new imaging technologies: green: no changes during one year, blue: surface loss of up to 20 mm, yellow until red: surface growth of up to 1 mm.

The „Opto-technical Monitoring” from the University of Bamberg helps to evaluate new conservation methods using nanomaterials

Nanomaterials applied e.g. to the surfaces of ancient cathedral stones might be a promising new technology for conservation work. They are tested in the international project Nano-Cathedral. But do they work? In order to find out, Dr. Rainer Drewello, professor of Building Preservation Sciences at the University of Bamberg, together with his colleague Max Rahrig, developed a process known as „Opto-technical Monitoring” which combines various imaging methods.

„Imaging technology is already being used in heritage conservation,” explains Drewello, „but until now, it had been all but impossible to test new materials used for stone conservation without destroying at least part of the stonework by extracting samples.”

Using the new lighting technology, Drewello can effectively execute a non-destructive and contact-free analysis of an approximately two-square-meter surface. Opto-technical Monitoring is based on a combination of high-resolution 3D imaging and VIS, ultraviolet, and infrared photography.

Whereas high-resolution 3D images serve to measure a surface and record its condition with an accuracy of 0.3 mm, the VIS color photography reveals variations in surface coloring. UV fluorescence photography and infrared photography make inorganic and organic foreign substances present on the surfaces visible. These can be preservative coating materials or biological growth such as bacterial films, lichens or mosses.

Max Rahrig and his colleague Anna Luib during research at the Oslo Opera House.

Together, these 4 techniques provide a complete image that had never before been possible in heritage conservation. By layering images that were rendered at different times, scholars are able to make comparisons and recognize changes in the stone.

The researchers are hoping that the international, interdisciplinary Nano-Cathedral project and its 6.3 million € from EU funding will make a significant contribution to the preservation of Europe’s cultural heritage. The project, in which Drewello and Rahrig collaborated with 18 partners from 6 European countries, was completed in 2018 after a 3-year runtime.

The nanomaterials developed in the project are currently being made market-ready and the new monitoring techniques will be used as a quality assurance mechanism involving ongoing measurements to determine the materials’ long-term benefits.

Source: University of Bamberg

Pictures: Max Rahrig, Katrin Vill, Christof Altmann/KDWT/Universität Bamberg

(19.03.2019, USA: 03.19.2019)