The influence of microfilamentous fungi on wooden organ pipes: One year investigation

Highlights

• Different fungal strains were isolated from a wooden contaminated organs.

• 8 wooden model pipes were artificially contaminated with these isolates for one year.

• Fungi colonized the wooden pipes and primarily degraded the joints glue.

• A novel portable sound controller was developed in order to monitor the pipes.

Abstract

Wooden pipe organs are precious objects of cultural heritage the degradation of which has been very poorly studied. Fungal strains recovered from an organ dating back to the 19th century included Alternaria mali, Eurotium cristatum, Aspergillus amstelodami, Penicillium crustosum and Aspergillus sydowii. These isolates were used to artificially contaminate wooden pipes treated with linseed oil varnish and varnish-free. The pipes were incubated at different temperatures and relative humidity for one year. The pipes, incubated at a high relative humidity (70–75%), collapsed due to the biodegradation of glued joints. After one year, inoculated strains (Alternaria mali, Penicillium crustosum and Aspergillus sydowii) as well as some non-inoculated Talaromyces rugulosus, Paecilomyces formosus, Cladosporium cladosporioides, Aspergillus versicolor and Epicoccum nigrum were recovered from the pipes. Few strains exhibited lignolytic activity, while almost all were able to hydrolyze the rabbit glue used to join the wood elements of the pipes. A newly developed portable pipe-sound controller did not detect differences of sound spectra between the uncontaminated and the few surviving contaminated pipes. In this study we have demonstrated that glue degradation was critical for pipe preservation and it can be tremendously accelerated above a certain relative humidity threshold. Therefore, it is important to apply a monitoring strategy able to check the environmental conditions, microbial contamination and pipe sound alteration in order to preserve these valuable and rare cultural heritage objects.

Introduction

Wooden pipe organs are not uniformly spread in European countries, but there are different areas of Central Europe, including Italy, where they were more widely diffused especially during the Renaissance and the Baroque periods, embellishing churches and aristocratic residences (Jakob, 1997). Many churches in Slovakia also conserved this particular musical heritage (Mayer, 2009, Štafura et al., 2014) which in several circumstances are seriously contaminated by microfilamentous fungi.

Construction materials of organ pipes are usually biodegradable materials like leather, wood, a variety of glues made from plant- or animal-derived materials, and the degradation of these materials affects directly the technical properties, as well as the sound quality of the instruments. This study was motivated by the specific and extensive contamination of microscopic fungi on the wooden elements (including wooden organ pipes) of a historical musical organ in the city of Spišská Nová Ves (Slovakia), the origin of which dates back to the early 19th century. The fungi were recovered from all types of wood, whether Picea abies, or Quercus sp. etc. (Fig. 1a–c).

The average relative atmospheric humidity in autumn and winter in the proximity of the wooden organ was around 60%–70%. The window panes on the back side and around the organ were made of transparent glass which promoted water condensation (Fig. 1d). This phenomenon occurred when the outside temperature was higher than the temperature inside the sacral place, producing a moist environment on the surface of the wooden organ pipes favorable for the growth of microfilamentous fungi.

In addition, many wooden components of the pipe organ were impregnated, on their surfaces, by a varnish oil preservative. Probably this oil layer of linseed oil (commercial name Fermež) diluted with different solvents such as toluene was applied in previous restoration operations. Such a compound could create an environment favorable for collecting hygroscopic particles including microscopic fungi. Other wooden organ elements, e.g. the organ case, without oil varnish did not exhibit visible fungal colonization.

This study on the impact of microscopic fungi on different model wooden pipes materials was encouraged also by the fact that only one investigation (Scheiding et al., 2008) on this topic was reported before in the literature. In addition, we didn't find any studies dealing with the modification of the sound of organ pipes caused by the actions of microscopic fungi. A portable pipe-sound controller (URHAN 300P) was developed for these investigations.