EGU22-8670, updated on 28 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Mn-rich Black Patina Formation on Built Heritage in Humid Areas

David Martin Freire-Lista1,2, Rebeca Blanco-Rotea3, Maria do Rosário Costa1,4, and Jorge Sanjurjo-Sánchez5
David Martin Freire-Lista et al.
  • 1Centro de Geociências da Universidade de Coimbra., Geology, Vila Real, Portugal (
  • 2UTAD Universidade de Trás-os-Montes e Alto Douro. Quinta de Prados, 5001-801 Vila Real, Portugal (
  • 3Laboratório de Paisagens, Património e Territorio (Lab2PT), Universidade do Minho. Unidade de Arqueologia, Edifício dos Congredados. Avda Central, 100. 4710-229 Braga (
  • 4GeoBioTec — Geobiociências, Geotecnologias e Geoengenharia Research Centre, Campus de Santiago, 3810-193 Aveiro, Portugal
  • 5University Institute of Geology, University of A Coruña. Campus de Elviña, 15071 A Coruña, Spain (

This study aims to characterise the decay due to black patinas of Santalla de Bóveda Monument (Lugo, Northwest of Galicia, Spain).

Manganese is one of the most abundant elements on Earth, and the granite on which Santalla de Bóveda Monument was built (used as building material of the monument) has considerable amounts of Manganese. This monument shows black patinas on the surface of its building materials (mortars and granites).

Mortars and granite with Mn-rich black patinas were analysed in their chemical, mineralogical and petrographical properties (polarizing and scanning electron microscopes, X-ray diffraction and X-ray fluorescence). In addition, the water from springs near the monument was analysed.

According to the experimental study results, it was observed that rich Mn-oxide crusts are presumably induced by bacteria. That is, the oxidation of Mn fuels the growth of chemolithoautotrophic microorganisms, which need water to live. These patinas of biogenic Mn-oxide minerals presented different shapes, nano-dimensions, with low degree of crystallinity, and appear to be composed of manganese oxides such as birnessite, ramsdellite and groutellite. They were associated with large amounts of extracellular polymeric substances exuded by filamentous bacterial communities, which serve as nuclei for preferential precipitation of manganese oxides on the extracellular sheaths, as seen in scanning electron microscope analyses.

Mn required for patina formation likely derives from the reductive dissolution in water of Mn-rich minerals, as suggested by the mineralogy and chemistry of Mn-rich phases present in the building granite and mortars. Mn migrates to the exposed surface of building materials, where they are re-oxidized via biological processes. Patinas developing over time result from the alternation of wetting-reducing and drying-oxidizing cycles.

Water absorption, dampness and black patinas are among the most common and critical problems when it comes to decay of both cultural heritage and modern buildings. The climate and specifically the humidity are determinant for the development of Mn-rich black patinas. Results revealed that chemical composition and porosity played a major role in the development of biological activity that generates the black patinas of manganese oxides on mortars and granite.

How to cite: Freire-Lista, D. M., Blanco-Rotea, R., Costa, M. D. R., and Sanjurjo-Sánchez, J.: Mn-rich Black Patina Formation on Built Heritage in Humid Areas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8670,, 2022.