Degradation of ancient Maya carved tuff stone at Copan and its bacterial bioconservation
MetadataShow full item record
AuthorElert, Kerstin; Ruiz Agudo, Encarnación; Jroundi, Fadwa; González Muñoz, María Teresa; Rodríguez Navarro, Carlos Manuel
Elert, K., Ruiz-Agudo, E., Jroundi, F. et al. Degradation of ancient Maya carved tuff stone at Copan and its bacterial bioconservation. npj Mater Degrad 5, 44 (2021). [https://doi.org/10.1038/s41529-021-00191-4]
SponsorshipSantander Program for the Research and Conservation of Maya Sculpture, at the David Rockefeller Center for Latin American Studies (DRCLAS), Harvard University; Spanish Government European Commission RTI2018-099565-B-I00; Junta de Andalucia RNM-179- BIO 103; University of Granada, Unidad Cientifica de Excelencia UCE-PP2016-05
Much stone sculptural and architectural heritage is crumbling, especially in intense tropical environments. This is exemplified by significant losses on carvings made of tuff stone at the Classic Maya site of Copan. Here we demonstrate that Copan stone primarily decays due to stress generated by humidity-related clay swelling resulting in spalling and material loss, a damaging process that appears to be facilitated by the microbial bioweathering of the tuff stone minerals (particularly feldspars). Such a weathering process is not prevented by traditional polymer- and alkoxysilane-based consolidants applied in the past. As an alternative to such unsuccessful conservation treatments, we prove the effectiveness of a bioconservation treatment based on the application of a sterile nutritional solution that selectively activates the stone ' s indigenous bacteria able to produce CaCO3 biocement. The treatment generates a bond with the original matrix to significantly strengthen areas of loss, while unexpectedly, bacterial exopolymeric substances (EPS) impart hydrophobicity and reduce clay swelling. This environmentally-friendly bioconservation treatment is able to effectively and safely preserve fragile stones in tropical conditions, opening the possibility for its widespread application in the Maya area, and elsewhere.