A Case Study of the Compatibility of Biocidal Cleaning and Consolidation in the Restoration of a Marble Statue

The two major components of the restoration of an 1884 outdoor marble sculpture in New Orleans were cleaning the extensive biological growth and consolidating the fragile surface. New Orleans’ semi-tropical climate encourages the growth of microorganisms that can be damaging to the stone. The biological growth on the sculpture of Margaret Haughery, a philanthropist (Figures la and lb), was found to include algae, fungi, hemi-lichens and lichens, particularly Caloplaca feracissima H. Magn., which greatly altered the white Carrara marble surface appearance. In addition, some organisms had penetrated up to 10 mm into the stone along larger cracks (Figure 2) and 0.05 mm beneath loose surface crystals. Their physical presence contributed to the mechanical degradation of the marble. They also contributed to the stone’s chemical degradation by etching the marble crystals with acidic secretions (Figure 3).