Microblasting of powdered lignocellulosic particles: Cleaning of a wooden joint cover of a medieval coffered ceiling

Abstract

Mechanical methods used for cleaning unpolychromed wooden heritage in conservation-restoration rely on procedures that entail pressure and friction, potentially leading to erosion or material loss on the treated surface. In addition, certain methods, such as the use of sponges or erasers, very often leave residues that could affect the long-term conservation of wood due to their chemical composition. The aim of this work is to assess the feasibility of using microblasting with powdered lignocellulosic particles for cleaning unpolychromed wood on a heritage artwork. The investigation aims to evaluate the advantages and drawbacks of this technique as a sensitive and sustainable alternative to the most common techniques used by conservator-restorers for unpolychromed wood cleaning. The cleaning results of microblasting of lignocellulosic particles are qualitatively compared to those achieved by traditional dry-cleaning techniques on wood. This study is based on previous research that examined the effects of this technique on non-heritage wooden samples using hazelnut and almond shells, cork and pure cellulose powdered particles. The investigation aimed to assess potential morphological surface changes and to determine the degree of cleaning qualitatively without causing damage to the wood surface. Additionally, the study allowed the development of a cleaning protocol by selecting the specific particle size, and by adjusting pressure, an- gle, distance and time to surface soiling characteristics and wood typology according to the limited bib- liographic references available. From these results, tests were conducted on the back side of a wooden joint cover dating back to between the 14th and 16th centuries from one of the ceilings of the Monastery of Santa María de Pedralbes. The joint cover was weakened and affected by fungi and woodworm after centuries of outdoor climate exposure. To evaluate the cleaning efficiency and the resulting effects on wood, the surface was analysed by digital optical microscopy and scanning electron microscopy before and after cleaning. Star diagrams were also made to assess the fulfilment of the cleaning criteria selected for the study. Results indicate that when the technique is applied properly, an appropriate cleaning level can be achieved without compromising the fragile treated surface and with negligible presence of residues. Therefore, this approach emerges as a promising and environmentally friendly technique, respectful to the integrity of the heritage wooden artworks.