Zprávy památkové péče 2018, 78(3):252-259 | DOI: 10.56112/zpp.2018.3.09

Cleaning the sculpture of St. John of Nepomuk from Prague's Pohořelec using a laser

Jakub Ďoubal

Fakulta restaurování Univerzity Pardubice

The article summarizes the basic principles of laser cleaning and presents its practical application in the cleaning of the valuable early Rococo sculptural group of St. John of Nepomuk from the Pohořelec area of Prague. The sculpture was created in 1752 by the Prague sculptor Jan Antonín Quitainer. The concept of the restoration was chosen on the basis of a comprehensive restoration survey with special attention paid to the challenge of cleaning, which was conducted on the basis of thorough examinations and laboratory tests. For the silicate sandstones, the impurities consisted predominantly of dust and soot bound in a silicate film and firmly bonded to the substrate. In practice, the removal of this insoluble film consists in the use of either a chemical cleaning using an ammonium fluoride which dissolves the silicate film and allows it to be removed by subsequent washing, or an abrasive cleaning using the abrasive characteristics of various types of abrasives driven by air or water. This description of the cleaning process alone makes it clear that both methods pose a significant risk to the substrate. For these reasons, a laser equipment has been previously developed for cleaning first carbonate and subsequently silicate minerals. Electron microscope photographs, as well as protrusions and recesses, show the results of the cleaning tests and an assessment of the methods of cleaning in question. The most sensitive method of cleaning using laser beams (Q-switched, ND: YAG Thunder Art Laser) was selected and was used to clean the sculpture in connection with the overall concept of the item's restoration. In this case, the cleaning contributed to an improvement of the physical properties of the surface and to the visual unification of the work, as well as to the preservation of its aesthetic qualities. The photographic documentation shows the cleaning process, including the details and the final state. The final discussion summarizes the experiences and risks of using the tested cleaning methods.

Keywords: cleaning sculpture monuments, laser cleaning stones, sculpture of St. John of Nepomuk in Prague's Pohořelec

Published: September 1, 2018  Show citation