Gert Nuyts

Room-Temperature Study of Iron Gall Ink Impregnated Paper Degradation under Various Oxygen and Humidity Conditions: Time-Dependent Monitoring by Viscosity and X-ray Absorption Near-Edge Spectrometry Measurements

Many western manuscripts were written using iron gall inks. These inks can damage the paper via two major mechanisms: (a) acid hydrolysis, enhanced by humidity, and (b) oxidative depolymerization provoked by the presence of oxygen and free iron(II) ions. The degradation of unsized Whatman paper impregnated with different combinations of iron sulfate, gallic acid, and gum arabic was studied at room temperature in order to assess the relative importance of each mechanism. The samples were stored in various environments including a dry and/or an oxygen-free atmosphere. The cellulose depolymerization was monitored by viscometry and related to changes in the oxidation state of iron, determined by X-ray absorption near-edge spectrometry. The results indicate that residual amounts of oxygen (less than 0.1%) promote cellulose depolymerization, whereas the level of relative humidity has no impact. The cellulose depolymerization also appears closely correlated to oxidative mechanisms. Regarding the oxidation of iron, it only occurs in the simultaneous presence of oxygen and moisture, suggesting the occurrence of rustlike oxidative mechanisms. Finally, the presence of gallic acid has a strong influence, which is only partially explained by its capacity to reduce iron(III) to iron(II).

Evaluation of manganese-bodies removal in historical stained glass windows via SR-μ-XANES/XRF and SR-μ-CT

The speed and effectiveness of a conservation treatment used for stained glass windows have been investigated. Dark-coloured Mn-rich stains can be found in the alteration layer of ancient glass artefacts and cause the surface to turn brown/black: this phenomenon is known as Mn-browning or Mn-staining. While in glass manganese is present in the +II or +III oxidation states, in the Mn-rich bodies, manganese is in a higher oxidation state (+IV). In restoration practice, mildly reducing solutions are employed to eliminate the dark colour and restore the clear appearance of the glass. In this paper the effectiveness and side effects of the use of hydroxylamine hydrochloride for this purpose are assessed. Archaeological fragments of stained glass windows, dated to the 14th century and originating from Sidney Sussex College, Cambridge (UK), were examined by means of synchrotron radiation (SR) based microscopic X-ray Absorption Near-Edge Spectroscopy (μ-XANES) and microscopic X-Ray Fluorescence (μ-XRF) and with high resolution computed absorption tomography (μ-CT) before, during and after the treatment. The monitoring of the glass fragments during the treatment allows us to better understand the manner in which the process unfolds and its kinetics. The results obtained reveal that the hydroxylamine hydrochloride treatment is effective, but also that it has a number of unwanted side effects. These findings are useful for optimizing the time and other modalities of the Mn-reducing treatment as well as minimizing its unwanted results.

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.

Micro-XANES study on Mn browning: use of quantitative valence state maps

Historical glass, especially non-durable medieval glass, can undergo corrosion. This sometimes results in the formation of dark-coloured manganese-rich inclusions that reduce the transparency of the glass. While unaltered bulk glass contains manganese mainly present in the +II valence state, inside the inclusions Mn is present in higher valence states (+III to +IV). Two different strategies may be considered by conservators when aiming to improve the transparency. One is based on the reduction of highly oxidised black/brown compounds using mildly reducing solutions, while the other focuses more on the extraction of manganese from the inclusions by the application of chelating agents. In this paper, a method for quantitative mapping of the Mn speciation inside partially corroded historical windowpanes based on X-Ray Absorption Near-Edge Structure (XANES) spectroscopy is discussed. The calibration of such Mn valence state maps based on the combo method, a fairly reliable way to determine the oxidation state, is described in more detail. This method is used to evaluate the effect of reducing treatments on historical glass, dated to the 14th century and originating from Sidney Sussex College (Cambridge, UK), suffering from Mn browning. Glasses were examined by means of Synchrotron Radiation (SR) based microscopic X-Ray Absorption Near-Edge Structure (μXANES) spectroscopy and microscopic X-Ray Fluorescence (μXRF). X-Ray elemental distribution maps of glass cross-sections are recorded at different energies, while Mn K-edge spectra are used to convert these into Mn valence state (VS) maps. Such valence state maps will allow evaluation of a reducing treatment.

Combined Computed Nanotomography and Nanoscopic X-ray Fluorescence Imaging of Cobalt Nanoparticles in Caenorhabditis elegans

Synchrotron radiation phase-contrast computed nanotomography (nano-CT) and two- and three-dimensional (2D and 3D) nanoscopic X-ray fluorescence (nano-XRF) were used to investigate the internal distribution of engineered cobalt nanoparticles (Co NPs) in exposed individuals of the nematode Caenorhabditis elegans. Whole nematodes and selected tissues and organs were 3D-rendered: anatomical 3D renderings with 50 nm voxel size enabled the visualization of spherical nanoparticle aggregates with size up to 200 nm within intact C. elegans. A 20 × 37 nm2 high-brilliance beam was employed to obtain XRF elemental distribution maps of entire nematodes or anatomical details such as embryos, which could be compared with the CT data. These maps showed Co NPs to be predominantly present within the intestine and the epithelium, and they were not colocalized with Zn granules found in the lysosome-containing vesicles or Fe agglomerates in the intestine. Iterated XRF scanning of a specimen at 0° and 90° angles suggested that NP aggregates were translocated into tissues outside of the intestinal lumen. Virtual slicing by means of 2D XRF tomography, combined with holotomography, indicated presumable presence of individual NP aggregates inside the uterus and within embryos.

Lost transparency! Weathering phenomena on the archaeological window glass collection of the Cistercian Abbey of the Dunes - Koksijde (Belgium)

As far as Belgium and archaeological window glass is concerned, the most important site is the Dunes Abbey, a former Cistercian abbey near the Flemish coastline. The collection contains approximately 15,000 fragments dating from the 13th to the 16th century. This glass was exposed to atmospheric weathering while in situ for several hundred years, buried for up to 400 years, excavated by different individual excavators in different eras and for over half a century stored in uncontrolled conditions. Moreover, different conservation treatments have been applied to the glass. Due to this, the collection was in a friable condition and we assume half of it has already been completely lost. The remaining collection retains fragments whose condition ranges between almost perfectly preserved material to being completely weathered to the point that no original glass survives. In this research, an important asset is recognizing what has already been lost and maximizing what is still available. During recent conservation and stock making campaigns, the different weathering phenomena were separated into 9 groups based on empirical criteria and detailed registration. As a first step to further investigation of the weathering processes, quantitative SEM-EDX analyses are used to give better insight into the chemical composition of these groups. The aim is to bridge the gap between interpretative archaeologically and archaeological science and to develop a common terminology to evaluate the complexity of weathering phenomena in archaeological window glass collections which can be used as a tool for the assembling and interpretation of these collections.