Wendy Meulebroeck

Iron speciation in soda-lime-silica glass: a comparison of XANES and UV-vis-NIR spectroscopy

Scientific analyses of ancient glasses have been carried out for many years using elemental chemical analysis. However, it is known that the control of the redox conditions in the glass melt has a strong implication on the final hue of glass because it affects Fe2+/ΣFe. Therefore an increasing number of studies on the redox conditions have been published in recent years by means of synchrotron based X-ray absorption spectroscopy. This is a technique which is not easily accessible and requires dedicated facilities. In this paper we describe an alternative approach by means of optical absorption spectroscopy. We synthesised 10 soda-lime-silica glasses with known redox conditions and iron concentration to calibrate the absorption at 1100 nm as a function of Fe2+ concentration. The linear extinction coefficient was also determined. These glasses were also studied by means of X-ray Absorption Near Edge Structure (XANES) spectroscopy. Electron paramagnetic resonance spectroscopy was additionally used as an ancillary method to verify the quality of our data. Furthermore 28 samples from real archaeological samples were analysed by XANES and optical spectroscopy as a case study. The Fe2+/ΣFe values obtained were compared and demonstrated that the two techniques were in good agreement with each other. Optical spectroscopy can be applied in situ with moderate sample preparation to determine the concentration of Fe2+. To investigate the redox conditions, especially as a first screening approach, this methodology is an important tool to take into consideration before applying more sophisticated techniques such as XANES, which is more elaborate and requires high-tech resources.

A XANES study of chromophores: the case of black glass

We studied the Fe K-edge X-ray absorption near edge (XANES) spectra of several Roman black glass fragments in order to determine the Fe3+/ΣFe ratio of these materials. The selected archaeological glass samples cover the period 1st–5th century AD in nine different sites of the North Western provinces of the Roman Empire. The fragments belong to two different compositional groups demonstrating a diachronic evolution: early Roman HMG (High Magnesia Glass) and Roman Imperial LMG (Low Magnesia Glass). The first group contains natural Fe levels (below 2 wt% as Fe2O3), while the LMG has concentrations above 5 wt%. This difference is also reflected by Fe3+/ΣFe values. Low iron glass was produced under strongly reducing conditions in order to obtain the black colour, with average Fe3+/ΣFe values ≈ 0.17. LMG glass is somewhat more oxidised (Fe3+/ΣFe ≈ 0.4–0.5). While HMG glass required active control of the furnace environment, LMG was made under ambient atmosphere and its higher oxidation degree is mainly determined by the chemistry of the raw glass.

Photonics enhanced sensors for food monitoring: part 1

This paper is the first part in a series of three where the authors show how photonics based food sensors can contribute to the quality control and safety of solid and liquid food products. In this first part, we describe the theoretical aspects of the various physical phenomena that can occur during food screening together with their related measurement setups. In addition, this document contains information regarding data processing and the concerned sensing platforms.

Authenticity screening of stained glass windows using optical spectroscopy

Civilized societies should safeguard their heritage as it plays an important role in community building. Moreover, past technologies often inspire new technology. Authenticity is besides conservation and restoration a key aspect in preserving our past, for example in museums when exposing showpieces. The classification of being authentic relies on an interdisciplinary approach integrating art historical and archaeological research complemented with applied research. In recent decades analytical dating tools are based on determining the raw materials used. However, the traditional applied non-portable, chemical techniques are destructive and time-consuming. Since museums oftentimes only consent to research actions which are completely non-destructive, optical spectroscopy might offer a solution. As a case-study we apply this technique on two stained glass panels for which the 14th century dating is nowadays questioned. With this research we were able to identify how simultaneous mapping of spectral signatures measured with a low cost optical spectrum analyser unveils information regarding the production period. The significance of this research extends beyond the re-dating of these panels to the 19th century as it provides an instant tool enabling immediate answering authenticity questions during the conservation process of stained glass, thereby providing the necessary data for solving deontological questions about heritage preservation.

Unravelling provenance and recycling of late antique glass from Cyprus with trace elements

Earlier research has shown that several common late antique glass types circulate in Cyprus between the fifth and the seventh century AD, specifically Levantine 1, HLIMT, HIMTa, HIMTb and Egypt 1, HIT, Roman and a plant ash glass. By investigating the glass material from Yeroskipou-Agioi Pente, Maroni-Petrera, and Kalavasos-Kopetra, we aimed to refine the chemical groups present within three late antique Cypriot sites and define the relations between trace elements obtained from LA-ICP-MS. Our data demonstrate compositional patterns that can be exploited to provenance late antique glass by investigating the REE-bearing mineral fractions, the amount of zircon and the carbonaceous fraction of the sand. In addition, Nb and Ti display a strong linear relation which depends on the glass type. Finally, the paper discusses the occurrence of glass recycling on the island and how this activity influenced the concentration levels of specific trace elements. Our study thus sets out an analytical framework to identify recycling events tailored on each compositional type.

Terranova, a Popular Stone Imitation Cladding: Strategies and Techniques for Restoration

At the beginning of the 20th century, the application of innovative finishes on facades became a popular phenomenon in Belgium. Decorative renders were frequently used to hide the aesthetically imperfect structure and to imitate valuable natural stone features. In order to create the appearance of French stone, ingredients such as lime, mica and crushed natural stone were added to white cement. Afterwards, the surface was scratched or scraped to shape a rough texture. As a result, a convincing ‘simili-pierre’ or ‘stone imitation’ masonry was obtained, after drawing simulated joints into the wet render layer. Today, these imitation finishes suffer in most cases from discoloration, cracks, peeling off and other damage which has completely changed the initial perception. Since knowledge is lacking concerning their composition, properties and application techniques, many questions remain unanswered within the conservation area. As a consequence, incorrect decisions may be made during restoration campaigns, which may lead to additional damages. A remarkable example of a simili-pierre render is the former commercial product Terranova, which is the focus of the research. By means of literature studies, the exploration of historical patents, laboratory analysis of representative samples and a comparative research between similar claddings, this paper proposes legitimate solutions to revitalize the Terranova finishes. It is found that both original mortar formulas and historic application guidelines are key elements which form a fundamental contribution to restore stone imitating renderwork in a sustainable way, with respect for authenticity issues.