The San Carlo Colossus: An Insight into the Mild Galvanic Coupling between Wrought Iron and Copper.

The San Carlo Colossus, known as San Carlone, is a monument constituted by an internal stone pillar support to which a wrought iron structure is attached. Embossed copper sheets are fixed to the iron structure to give the final shape to the monument. After more than 300 years of outdoor exposure, this statue represents an opportunity for an in-depth investigation of long-term galvanic coupling between wrought iron and copper. Most iron elements of the San Carlone appeared in good conservation conditions with scarce evidence of galvanic corrosion. In some cases, the same iron bars presented some portions in good conservation conditions and other nearby portions with active corrosion. The aim of the present study was to investigate the possible factors correlated with such mild galvanic corrosion of wrought iron elements despite the widespread direct contact with copper for more than 300 years. Optical and electronic microscopy and compositional analyses were carried out on representative samples. Furthermore, polarisation resistance measurements were performed both on-site and in a laboratory. The results revealed that the iron bulk composition showed a ferritic microstructure with coarse grains. On the other hand, the surface corrosion products were mainly composed of goethite and lepidocrocite. Electrochemical analyses showed good corrosion resistance of both the bulk and surface of the wrought iron, and galvanic corrosion is not occurring probably due to the iron's relatively noble corrosion potential. The few areas where iron corrosion was observed are apparently related to environmental factors, such as the presence of thick deposits and to the presence of hygroscopic deposits that create localized microclimatic conditions on the surface of the monument.

Protective treatments for copper alloy artworks: preliminary studies of sodium oxalate and limewater effectiveness against bronze disease.

Nantokite (CuCl) locked inside subsurface micro-pits has been recognised as the driving force to the form of corrosion called bronze disease. The use of the traditional corrosion inhibitor benzotriazole is questioned because of toxicity. So there is a need for alternative conservation treatments. This work is focused on the experimental design to test the effectiveness of sodium oxalate followed by treatment with limewater to face bronze disease on outdoor bronzes. A number of foundry bronze coupons were exposed to weathering at Genoa Experimental Marine Station (GEMS) exposure site and sprayed twice a week with a 5% NaCl solution for the first 124 days. After 562 days of natural weathering, the patinas on coupons were characterised with non-destructive techniques (NDT) and the presence of nantokite was verified. We designed a workflow, as similar as possible to conservation treatments on real artworks, to test a 3% w/v sodium oxalate treatment with two different application times, with or without limewater, on the coupons. The effectiveness of the treatments was analysed by comparison of surface properties by several NDT measurements. A statistical approach and XRD measurements directly on the corroded bronze surfaces are suggested as an effective way to characterise and compare the overall behaviour of bronze disease treatments for conservation.

Enriching the knowledge of Ostia Antica painted fragments: a multi-methodological approach.

This paper presents the study of selected painted fragments from different contexts of Ostia Antica city, dating between 2nd century BCE and the end of the 1st century CE. The aim is to identify the raw materials used and to understand the execution techniques through a non-invasive protocol including techniques based either on multiband imaging (Visible-VIS, Ultraviolet induced Luminescence - UVL and Visible Induced Luminescence - VIL) and single spot analyses (Fiber Optic Reflectance Spectroscopy- FORS and portable X-Ray Fluorescence spectrometry - XRF). The most representative and interesting fragments were sampled for further studies with laboratory techniques such as optical microscopy (OM) and electron microscopy (SEM), Fourier Transform Infrared and micro-Raman Spectroscopies (FT-IR and µRaman). The extensive use of non-invasive techniques, even working on fragments, is proved to be the most robust and effective approach enabling the analysis of a high number of areas, dramatically increasing the statistical meaning of the collected data. The elaboration of such a huge number of data allows highlighting differences and similarities, thus achieving a more realistic overview of the materials composition and addressing the sampling to the more significant and complex areas.

A multi-analytical approach for the study of red stains on heritage marble.

Red stains are a common discolouration on stone cultural heritage all over the world. These are very difficult to remove and little is known about the reddish pigmentation. Numerous red stains were mapped on the Baptistery of San Giovanni in Florence, one of the most important monuments in Italy. This paper is focused on red stains on marble stone and the results of a detailed multidisciplinary approach are presented. Several analytical and investigation techniques (such as optical microscopy, X-ray fluorescence mapping, X-ray micro-tomography, micro-Raman spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, microbial isolation, colorimetric measurements and isotopic analyses) were used to better understand the origin and processes involved in this kind of alteration. Analyses of the red stains led us to believe the presence of minium (lead tetroxide) and Pb are usually concentrated in the spaces between calcite grains. Red stains of Pb isotopic composition also overlap with data from Sardinian mines. These preliminary data seem to reinforce the suggestion of a source of lead from some metallic items (during restoration campaigns between 1938 and 1944, damaged parts were removed and replaced, and the new marble cladding was fixed with iron brackets treated with minium).

Environmental impact assessment on the stone decay in the archaeological site of Hierapolis (Denizli, Turkey).

The archaeological site of Hierapolis (Denizli province, Turkey) is unique in terms of the conservation of marbles and travertines. Environmental factors (i.e. interaction with thermal waters, high thermal stress, CO2 degassing) and geological aspects (presence of seismic faults, frequent earthquakes, formation of travertine) play a fundamental role in the durability and conservation state of the stone materials. This paper presents a multi-analytical approach aimed to identify the phenomena and causes of stone decay related to environmental conditions. The analyses of alteration and decay phenomena are discussed together with the monitoring of the main environmental parameters and with analyses of waters and gases present in the archaeological site. Finally, the need of a continuous monitoring of the environmental parameters affecting the archaeological site is stressed.