Ionic liquids against heritage deterioration
Micro-organisms are adept at colonising and deteriorating artistic and architectural heritage, resulting in considerable economic damage for museums and local authorities as well as private collectors. More importantly, this can lead to immeasurable cultural and social losses.
Nowadays, the increase in geotourism (for example, underground caves) has an increase in illumination of such environments, which favours the growth of autotrophic organisms such as cyanobacteria and algae.
An example of overgrowth of these autotrophic micro-organisms in caves associated with permanently installed lighting (lampenflora) is found in the bas-reliefs of the prestigious underground Vranken-Pommery Champagne cellar in Reims, France. These bas-reliefs were carved in chalk by the French sculptor Gustave Navlet between 1882 and 1885, and are listed as a UNESCO World Heritage Site. The winery organises numerous tours every day to present the galleries and the rooms containing the bas-reliefs, which were once illuminated by incandescent lamps and have now been replaced by LEDs. In addition, over the past 13 years, contemporary artworks have also been exhibited in different rooms of the winery, which has increased the need for artificial light. Some of the works even radiate light themselves, exacerbating the problem. The progressive expansion of the lampenflora has generated extensive biofilms, with greenish and reddish tones, which alter the natural beauty of the bas-reliefs and contribute to their deterioration. To solve this problem, microbial contamination is removed by a classic cleaning procedure, applying bicarbonate with the aid of an airbrush. However, the lampenflora is capable of recolonising the surface in a short time, generating biofilm on the bas-reliefs once again, which makes it necessary to carry out periodic cleaning every six months.
The aim of this research carried out by Scott G. Mitchell and Isabel Franco Castillo, researchers at the Instituto de Nanociencia y Materiales de Aragón (INMA), a joint institute of the CSIC and the University of Zaragoza, was to study and validate the use of polyoxometalate ionic liquids (POM-ILs) as transparent coatings to prevent the colonisation of lampenflora and protect the bas-reliefs. During this study, the activity of these compounds against different strains of algae and cyanobacteria was compared with the commercial product Preventol RI80, and it was demonstrated that the POM-ILs have greater microbicidal activity against these autotrophic strains than the commercial product. The experiments carried out to study the efficacy of the compounds were a combination of antimicrobial assays, colorimetry and chlorophyll fluorescence analysis, which showed how POM-ILs are more effective than Preventol RI80 in preventing the growth of algae and cyanobacteria for seven weeks. In addition, a test was carried out in more extreme conditions, more in line with the environment where the bas-reliefs are located and showed how one of the POM-ILs was able to prevent re-colonisation of the surface.
This work was made possible by international collaboration between Dr. Scott G. Mitchell (INMA), Dr. Stéphanie Eyssautier (URCA), and Prof. Dr. Carsten Streb (University of Mainz, Germany). In 2019 Scott was a visiting professor at URCA for two weeks and, in spring 2022, Stéphanie carried out a one-month research stay at INMA to characterise colonised chalk using the electron microscopy equipment available in the Laboratory for Advanced Microscopy (LMA). In March of 2022, the INMA-URCA team initiated a phase of on-site tests inside the underground Champagne cellar, in recently cleaned areas of the bas-reliefs, to evaluate the duration of POM-ILs activity in real environments.
These results are not only useful for professionals in the field of heritage conservation, but also for chemists looking for more sustainable solutions to prevent biodeterioration and contribute to heritage conservation. The INMA team is currently looking for opportunities to transfer these results to the commercial sector.
The work has been published in the journal International Biodeterioration & Biodegradation, a study on “New protective coatings against lampenflora growing in the Pommery Champagne cellar”. This work will be part of a Special Issue entitled “Current knowledge and old problems: Complexity and new perspectives on the biodeterioration of materials”.
“New protective coatings against lampenflora growing in the Pommery Champagne cellar”
Isabel Franco-Castillo, Archismita Misra, Sébastien Laratte, Maxime Gommeaux, Robin Perarnau, Nathalie Vaillant-Gaveau, Clément Pierlot, Carsten Streb, Scott G.Mitchell, Stéphanie Eyssautier-Chuine
International biodeterioration & Biodegradation 173 (2022) 105459
Available online 11 July 2022, Version of Record 11 July 2022.
DOI: 10.1016/j.ibiod.2022.105459
22/12/2022
