Alkylophosphates as low-cost inhibitors in silver tarnishing

Tarnishing is a process taking place in silver surface causing corrosion. This is due to the presence in the atmosphere, even in small amounts, of reactive species like water, sulphidric acid and carbonyl sulphide which can be physisorbed onto the silver surface thus reacting with it. We propose the use of alkylphosphates to protect the silver surface against corrosion: the polar head group should interact with the silver surface with the formation of a thin film of opportunely oriented surfactant molecules. This would shield the silver surface from the attack of reactive agents present in the atmosphere and from the adsorption of humidity water helped by the surfactant scarce hydrophilicity. The joint Raman and XPS experiments showed the protective action exerted by dibutylphosphate or bis (2-etylhexyl) phosphate according to the different sulphidizing conditions. Our discovery deserves to be tailored in cultural heritage where silver artefacts are generally precious and inimitable objects, but also in modern microelectronics where silver joints and conductors are used

Application of µ-Raman spectroscopy to the study of the corrosion products of archaeological coins

In this paper, a study of the corrosion products formed on archaeological bronze artefacts excavated in Tharros (Sardinia, Italy) is presented. The investigation was carried out by means of the combination of different analytical techniques, including optical microscopy, micro-Raman spectroscopy (µ-RS), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. The artefacts under study are three bronze coins from the Phoenician–Punic period that are deeply corroded due to the chloride-rich soil of the Tharros excavation site. µ-Raman spectroscopy was chosen to investigate the corroded surfaces of the artefacts because it is a non-destructive technique, it has high spatial resolution, and it makes it possible to discriminate between polymorphs and correlate colour and chemical composition. Through µ-RS, it was possible to identify different mineralogical phases and different polymorphs, such as cuprite (Cu2O), copper trihydroxychloride [Cu2Cl(OH)3] polymorphs, hydroxy lead chloride laurionite [PbCl(OH)] and calcium carbonate polymorph aragonite. The experimental findings highlight that micro-Raman spectroscopy can be used to provide further knowledge regarding the environmental factors that may cause the degradation of archaeological bronzes in soil.</p

A multianalytical approach to investigate stone biodeterioration at a UNESCO world heritage site: the volcanic rock-hewn churches of Lalibela, Northern Ethiopia.

A multianalytical approach combining Optical Microscopy (OM), Backscattered Variable Pressure Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy (VP-BSEM + EDS), Powder X-ray Diffractometry (PXRD), Raman Spectroscopy, and Microbiological techniques has been applied to characterize decay products and processes occurring at the surface of two rockhewn churches (Bete Gyorgis and Bete Amanuel) at the UNESCO’s World Heritage site of Lalibela, Northern Ethiopia. The two churches were carved into volcanic scoria deposits of basaltic composition. In their geological history, the Lalibela volcanic rocks underwent late to post-magmatic hydrothermal alteration together with partial laterization and are therefore characterized by a decay-prone highly vesicular microtexture with late stage to post-magmatic precipitation of secondary mineral phases (calcite–zeolite–smectite). The main objective of the study was to gain a better insight into the weathering products and mechanisms affecting the surface of the stone monuments and to assess the relative contribution of natural “geological” weathering processes versus biological/salt attack in stone decay at this unique heritage site. Results indicate that while the main cause of bulk rock deterioration and structural failure could be related to the stone inherited “geological” features, biological attack by micro- (bacteria) and/or macro- (lichens) organisms is currently responsible for severe stone surface physical and chemical weathering leading to significant weakening of the stone texture and to material loss at the surface of the churches walls. A prompt and careful removal of the biological patinas with the correct biocidal treatment is therefore recommended

A multianalytical approach to investigate stone biodeterioration at a UNESCO world heritage site: the volcanic rock-hewn churches of Lalibela, Northern Ethiopia.

A multianalytical approach combining Optical Microscopy (OM), Backscattered Variable Pressure Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy (VP-BSEM + EDS), Powder X-ray Diffractometry (PXRD), Raman Spectroscopy, and Microbiological techniques has been applied to characterize decay products and processes occurring at the surface of two rockhewn churches (Bete Gyorgis and Bete Amanuel) at the UNESCO’s World Heritage site of Lalibela, Northern Ethiopia. The two churches were carved into volcanic scoria deposits of basaltic composition. In their geological history, the Lalibela volcanic rocks underwent late to post-magmatic hydrothermal alteration together with partial laterization and are therefore characterized by a decay-prone highly vesicular microtexture with late stage to post-magmatic precipitation of secondary mineral phases (calcite–zeolite–smectite). The main objective of the study was to gain a better insight into the weathering products and mechanisms affecting the surface of the stone monuments and to assess the relative contribution of natural “geological” weathering processes versus biological/salt attack in stone decay at this unique heritage site. Results indicate that while the main cause of bulk rock deterioration and structural failure could be related to the stone inherited “geological” features, biological attack by micro- (bacteria) and/or macro- (lichens) organisms is currently responsible for severe stone surface physical and chemical weathering leading to significant weakening of the stone texture and to material loss at the surface of the churches walls. A prompt and careful removal of the biological patinas with the correct biocidal treatment is therefore recommended

Experimental and analytical study of gold parting processes used in ancient times

This paper provides an overview of our previous experimentation on ancient gold refining methods and reports recent developments. The research project is based on the use of experimental archaeology and analytical chemistry applied to probable ancient gold assaying and refining methods, in light of archaeological evidence and ancient textual sources. The aim is to understand the processes and their outcomes, supporting archaeological interpretations regarding gold metallurgy and related chemical processes in ancient times. Previous experimentation was carried out using different combinations of man-made and natural compounds, belonging to the sulphate-halide group (i.e. misy or ios skolekos and salt) and the phyllosilicate-halide class (i.e. powdered brick and salt), tested and characterized in the reagent-product chains and thermodynamically interpreted. Experiments were also undertaken to understand multipurpose procedures such as the collection-scorification-cementation method for the parting of gangue, accessory minerals and metals (copper and silver) from gold by the combination of different processes conducted sequentially in the same crucible. Recent results have been obtained on the following topics: Misy from Cyprus is evaluated in ancient texts as to be of high quality, and the experiments carried out after an analytical appraisal of specific mineral compounds has allowed us to hypothesize a possible reason: compositions such as copiapite-rich gossans and Devil's Mud (sulphide-based composition), make the cements particularly effective in the purification process; The use of stibnite as a parting agent has also been tested and interpreted, thus adding this typeof sulphide process to the possible procedures used, as well as suggesting a thermo-chemical interpretation of cementation with Devil's Mud; Preliminary analytical results of trace element variation before and after cementation of alluvial gold are proposed as possible fingerprints of transient processes used in the processing of gold and the fabrication of gold artefacts; The multi-purpose usage of ancient cement recipes for the removal of surface oxidation during the production of gold artefacts and for depletion gilding

A comprehensive strategy for exploring corrosion in iron-based artefacts through advanced Multiscale X-ray Microscopy

The best strategy to tackle complexity when analyzing corrosion in iron artefacts is to combine different analytical methods. Traditional techniques provide effective means to identify the chemistry and mineralogy of corrosion products. Nevertheless, a further step is necessary to upgrade the understanding of the corrosion evolution in three dimensions. In this regard, Multiscale X-ray Microscopy (XRM) enables multi-length scale visualization of the whole object and provides the spatial distribution of corrosion phases. Herein, we propose an integrated workflow to explore corrosion mechanisms in an iron-nail from Motya (Italy) through destructive and non-destructive techniques, which permit the extraction of the maximum information with the minimum sampling. The results reveal the internal structure of the artefact and the structural discontinuities which lead the corrosion, highlighting the compositional differences between the tip and the head of the iron nail