A black paint on the facade of a Renaissance building in Bergamo, Italy

Abstract

The first storey of the Casa dell'Arciprete in Bergamo, Italy, built of grey limestone, is today covered with a black paint layer. A detailed investigation of the morphology and composition of this layer was necessary in order to plan conservation work in 1993. Optical and scanning electron microscopy showed that the layer is very thin and closely follows the surface of the stone. Energy-dispersive X-ray (EDX) spectra of polished cross-sections did not reveal significant differences between the elemental composition of the stone and the black layer. Fourier transform infrared (FTIR) spectra of powdered samples provided evidence of a recent conservation treatment with an acrylic resin. Reflectance micro-FTIR analyses of polished cross-sections showed weddellite as the major component of the paint layer. Hydrolysis and gas chromatography-mass spectrometry (GC-MS) analysis of black samples showed the presence of an amino acid residue that has to be ascribed to an o'riginalproteinaceous binding medium. X-ray photoelectron spectroscopy (XPS) analysis of some black surface samples characterized the pigment phase as carbon of vegetal origin. Based on this investigation, it is hypothesized that the original paint layer was composed of carbon black applied with a proteina-'ceous medium, as recommended in ancient recipes. The organic medium ,is no longer the main component of the layer but present only in trace amounts. An oxidative process may have transformed the original binder into calcium oxalate. As the underlying stone was in good condition, the painted black layer was conserved.

A green approach to clean iron stains from marble surfaces

“…[46,51,52]. Their co-presence, often found on monument surfaces [53] long exposed to atmospheric pollutants, contributes to the formation of the characteristic 'patina' . Here the term "patina" indicates, without discrimination, all the sequential layers, of both biotic and abiotic origin, possibly deposited over the "noble patina", formed over the underlying carbonate stone and eventually protective against the progressive erosion due to acidic rain and aggressive atmospheric components [54,55].…”

Raman spectroscopy of natural oxalates at 298 and 77 K

“…The observation of the interface between calcite substratum and the above mentioned secondary minerals is an important step in the explanation of alteration process of artifacts of historic and artistic interest 37 . Studies of the black paint has shown the presence of oxalates in the paint with serious implications for remediation 38 .…”

Green Approach to Clean Marble Surfaces

“…As revealed by the number of peaks composing the carbon 1s signal, listed in Table 2, the blank surface of marbles is covered by carbonaceous contaminants, mainly consisting of aliphatic chains containing oxygen groups and some nitrogen and sulfur groups. Additional unspeci ed adsorbed compounds are grouped, in Table 2 assignments, as C organic belonging to the lower zone of Binding Energy typical of carbides, graphite, polycyclic and aromatic carbons [39,43,44]. Their co-presence, often found on monumental surfaces [45] long in uenced by atmospheric pollutants, contributes to the formation of the characteristic 'patina'.…”