Precipitation of manganese oxides on the surface of construction materials in the Khmer temples, Cambodia

Abstract

Background: In addition to the blackening caused by blue-green algae growth, other black areas on the surface of construction materials (e.g., sandstone, laterite and bricks) are frequently observed in the Khmer temples in Cambodia. A non-destructive on-site investigation was carried out using a portable X-ray fluorescence analyzer (pXRF). In addition, samples were taken from the buildings and were analyzed using an X-ray diffractometer (XRD) and a scanning electron microscope with an energy dispersive X-ray spectrometer, and were observed using a field emission scanning electron microscope. Results and conclusions:A non-destructive investigation using the pXRF revealed that this blackening was caused by manganese oxide precipitates. The precipitates contained small amounts of Ni, V, Zn, Y, K, Cl, S, Pb, and Cr. The XRD analysis indicated that the manganese oxides were mainly present as an amorphous phase, but some formed birnessite and todorokite. The manganese precipitates were mostly in a hexagonal plate form (100-300 nm), but some were in a rod-shape, which may have been caused by the activity of manganese oxidizing microbes. Preliminary experiments on removal of manganese oxide precipitates were conducted. The manganese oxide precipitates could be easily removed using a reducing agent such as an oxalic acid solution.

Black manganese-rich crusts on a Gothic cathedral

“…Colored organic compounds incorporated into the coatings can result in brownish or yellowish discolorations (Bonazza et al, 2007a;Brimblecombe and Grossi, 2009;Grossi and Brimblecombe, 2008). More recently, the growth of cyanobacteria (Bonazza et al, 2007b;Uchida et al, 2016), bacteria (Miller et al, 2012), and fungi (De Oliveira et al, 2011;Gorbushina et al, 1993;Saiz-Jimenez et al, 2012;Viles and Gorbushina, 2003) was also implicated in the discoloration of exposed stone materials.…”

“…However, in the last few years it was discovered that some black crusts on buildings in urban open areas are actually Mn-rich coatings (Grissom et al, 2014;Grüner et al, 2011;Livingston et al, 2016;Uchida et al, 2016;Vicenzi et al, 2016) with an as yet unknown genesis. These black crusts lack identifiable biogenic structures (Grissom et al, 2014;Livingston et al, 2016;Vicenzi et al, 2016) and are thus dissimilar to Mn-rich crusts found in cave environments, which had often been found to be of biogenic origin (Frierdich et al, 2011;Miller et al, 2012;Saiz-Jimenez et al, 2012;White et al, 2009).…”

The Tomb of the Diver and the frescoed tombs in Paestum (southern Italy): New insights from a comparative archaeometric study

“…Moreover, on the tombs 109, 110, 20, 23 and 76 (S1 Fig) superficial black patinas were observed. XRF spectra revealed the presence of manganese ( Fig 5A), likely due by the activity of manganese oxidizing microbes during the burial period [29]. This deterioration patinas ( Fig 5B), observed on tomb slabs preserved in the deposits and not yet subjected to a complete cleaning intervention, show evident differences in chemical composition with the unaltered black pictorial layers, displaying an enrichment in manganese, silicon, and iron content.…”

Characterization of an unusual black patina on the Neang Khmau temple (archaeological Khmer area, Cambodia): a multidisciplinary approach

“…The colours can vary from ochre through red, brown, violet to black, depending largely on the relative concentration of the metal oxides. [1,17,18] The temple appeared significantly covered by a black patina, distributed over all four facades, regardless of their exposure (south, east, north and west) ( Fig. 1), and covering a substantial part of the laterite walls protected from rainfall (despite the distribution of the biological patinas).…”

“…All monuments were built using sandstone, laterite and bricks. [1][2][3] Recent studies of the temples record the observation of various forms of deterioration of the stones. [4][5][6][7][8] The most common are biodeterioration processes because of microorganisms and plant colonization (bacteria, cyanobacteria, algae, lichens and higher plants), because of the climate and lush greenery of the area.…”