Combination of in situ spectroscopy and chemometric techniques to discriminate different types of Roman bricks and the influence of microclimate environment

Abstract

Red and yellow bricks are the wall-building materials generally used in Roman masonries. The reasons for the different coloration are not always understood, causing loss of crucial information both for the conservation and for the archaeological knowledge of the cultural sites. In this work, a combination of in situ analyses, employing portable Raman spectroscopy and handheld energy dispersive X-ray fluorescence (HH-ED-XRF) spectroscopy along with chemometric analysis, was carried out on ancient Roman bricks of the "Casa di Diana" building (Ostia Antica, Italy-130 CE). Specifically, the compounds and the characteristic elements, which describe each type of brick (red and yellow), were studied avoiding destructive or invasive sampling. The molecular analysis allowed us to identify the major and minor compounds that characterise the bricks (anatase, hematite, quartz, calcite and silicates). However, the elemental analysis gave more useful information. Thus, the complex HH-ED-XRF data matrix generated was treated by a specific principal component analysis (PCA) to identify behavioural differences of the coloured bricks. The results revealed that Ca and Fe are the discriminatory elements for the two types of bricks. The PCA outcomes suggest that the contribution of certain elements is different in the bricks (mainly Ca, P, Sr, As and S, for yellow bricks), which could indicate different raw materials. Even among bricks with the same red colour (Al, Si, Ti, K, Fe, Cr, Mn, Ni, Zn, Cu, Rb and Zr, seemed to be the elements linked to raw materials), as a function of the surface impacts (orientation and microclimate affect the salts' formation), a distinction was made. Furthermore, the PCA pointed out that the yellow bricks are those more affected by decaying processes (related with Ca, P and S), complying with the Raman spectroscopy results in which the efflorescences (gypsum) affect especially the surface of these types of bricks.

Egyptian metallic inks on textiles from the 15th century BCE unravelled by non-invasive techniques and chemometric analysis

“…The correlation between the presence and abundance of Fe, Mn and K in XRF spectra from a generic MP of typical spot size of 1 mm diameter, and their correspondence to the spatial distribution of the ink, is derived using “Box & Whiskers” representations and principal component analysis (PCA) (details are reported in SI) 23–26 . Box plots, shown in Fig.…”

“…Principal component analysis (PCA) is carried out on the whole set of XRF data to determine the correlations among the detected chemical elements and spot outliers, using the following variables:The list of measurement points and division into the inscription categoryThe different detected elements associated with the XRF peaksThe peaks’ intensities (integrated counts) 24–26 …”

High Frequency Data Acquisition System for Modelling the Impact of Visitors on the Thermo-Hygrometric Conditions of Archaeological Sites: A Casa di Diana (Ostia Antica, Italy) Case Study

“…The building, comprised of tabernae (a single room shop covered by a barrel vault within great indoor markets of ancient Rome; normally with overhead lighting openings) and cenacula (dining rooms), presents a very characteristic microclimate, especially inside two intercommunicating rooms (the Mithraeum and pre-Mithraeum ). The principal building materials are bricks and pozzolanic mortar aligned with the opus caementicium (Roman concrete, based on a hydraulic-setting cement, was a material used in construction during the late Roman Republic until the fading of the Roman Empire) technique [ 25 , 26 ]. The two rooms are characterized by different heights due to the presence at the sides of podium [ 26 ].…”

“…In the case of hypogea environments, characterized by a great stability (constant humidity and temperature) [ 25 ] and the abundance of nutrients providing a suitable niche for phototrophic microorganisms when combined with artificial illumination [ 15 , 24 ] visitors can be considered as a possible factor breaking that equilibrium state.…”

Neutrons for Cultural Heritage—Techniques, Sensors, and Detection

“…Cultural-Heritage artifacts, in particular ancient ones, still pose many interesting and important challenges, such as the correct determination of their historical and cultural timeframe, their location and method of production, and the choice of suitable treatments and environmental conditions for their restoration and conservation [1][2][3][4]. Amongst the large variety of physical and chemical techniques currently employed for the characterization of ancient objects, neutron-based methods are able to provide unique information, thanks to their particular interaction mechanisms with matter [5][6][7][8].…”