Capabilities and limitations of handheld Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) for the analysis of colourants and binders in 20th-century reverse paintings on glass

A first approach into the characterisation of historical plastic objects by in situ diffuse reflection infrared Fourier transform (DRIFT) spectroscopy

This research explores the potential of a portable instrumentation of diffuse reflection infrared Fourier transform (DRIFT) spectroscopy for the in situ characterisation of plastics cultural objects. As sampling has been increasingly questioned in the conservation field, the development of portable devices has been sought. Among them, infrared (IR) spectroscopy in reflection mode has been gaining a powerful position in conservation research. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) has been widely used for plastics, yet the strong contact required by the technique can make it inappropriate for flexible and/or fragile historic objects. Therefore, in this study, the potential of in situ DRIFT spectroscopy is assessed on both references and historical objects made of the same polymers - polyethylene (PE), polypropylene (PP) and polystyrene (PS). Plastic samples showing different characteristics such as refractive and absorption indexes and topography are also included. These different polymers and surface qualities are discussed as factors influencing the final spectra. In situ DRIFT proved to be very versatile as it could be applied in a variety of plastics and objects' shapes, does not require sampling nor an intimate contact as ATR. Moreover, specific bands and spectral profiles were identified as DRIFT markers of the polymers under study. The acquisition conditions for the in situ analysis were optimized and a pilot spectral database using different IR modes (transmission, ATR and DR) was created. Important information was collected, which allowed the polymer identification of the majority of the historical objects produced between the 1940s and 1980s, from a Portuguese private collection.

Potentiometric titration of microhydrolysis products of oils: A new low-cost methodology and investment for the analysis of oil binders present in works of art

The analysis of oil paints present in historical paintings is commonly carried out for research, authenticity and forensic purposes. This paper proposes potentiometric titration and calculation of the fatty acids concentrations with the aid of the Best7 program as an alternative technique to characterize the oil binders used in works of art. The method involves determining the ratio between the levels of palmitic (P) and stearic (S) acids present in the microhydrolysis products of commercial oil binders and paints. The microhydrolysis products were characterized, using FTIR spectroscopy, by displacement of the carbonyl band and the pKa values for the C16 and C18 in the system studied were determined. The P/S ratios found for the microhydrolysis products of linseed, palm and nut oils were 1.65, 5.91 and 2.42, respectively. For the commercial paints analyzed, values ranging from 1.34 to 1.98 were obtained, characterizing the presence of linseed oil. The values were confirmed by GC-MS and are in agreement with those reported in the literature for the oils investigated in this study.

Thin-layer chromatography/metal underlayer-ATR FTIR methodology for the study of synthetic dyes extracted from degraded wool fibres

The integration of an enhanced FTIR method with a multi-step micro-extraction protocol and the use of AgI@Au supports are proposed to analyse dyes in aged fibres.

Characterisation of oil and aluminium complex on replica and historical 19th c. Turkey red textiles by non-destructive diffuse reflectance FTIR spectroscopy

This work investigates historical and replica Turkey red textiles with diffuse reflectance infrared (DRIFT) spectroscopy to study the coordination complex between cellulose, fatty acids, and the aluminium ions that form the basis of the colour lake. Turkey red was produced in Scotland for around 150 years, and is held in many museum and archive collections. The textile was renowned for its brilliant red hue, and for its fastness to light, washing, rubbing, and bleaching. This was attributed to its unusual preparatory process, the chemistry of which was never fully understood, that involved imbuing cotton with a solution of aqueous fatty acids and then aluminium in the following step. Here we show, for the first time, a characterisation of the Turkey red complex on replica and historical textiles. The development of techniques for non-destructive and in situ analysis of historical textiles is valuable for improving understanding of their chemistry, hopefully contributing to better conservation and display practices. The results show the fatty acids condense onto the cellulose polymer via hydrogen bonding between the CO and OH of the respective compounds, then the aluminium forms a bridging complex with the fatty acid carboxyl. This contributes to an improved understanding of Turkey red textiles, and shows the useful application of handheld diffuse FTIR instruments for heritage textile research.

Investigation of the Cross-Section Stratifications of Icons Using Micro-Raman and Micro-Fourier Transform Infrared (FT-IR) Spectroscopy

The cross-section stratifications of samples, which were removed from six icons, are studied using optical microscopy, micro-Raman spectroscopy, and micro-Fourier transform infrared (FT-IR) spectroscopy. The icons, dated from the 14th to 19th centuries, are prominent examples of Byzantine painting art and are attributed to different artistic workshops of ​​northern Greece. The following materials are identified in the cross-sections of the icon samples using micro-Raman spectroscopy: anhydrite; calcite; carbon black; chrome yellow; cinnabar; gypsum; lead white; minium; orpiment; Prussian blue; red ochre; yellow ochre; and a paint of organic origin which can be either indigo ( Indigofera tinctoria L. and others) or woad ( Isatis tinctoria L.). The same samples are investigated using micro-FT-IR which leads to the following identifications: calcite; calcium oxalates; chrome yellow; gypsum; kaolinite; lead carboxylates; lead sulfate (or quartz); lead white; oil; protein; Prussian blue; saponified oil; shellac; silica; and tree resin. The study of the cross-sections of the icon samples reveals the combinations of the aforementioned inorganic and organic materials. Although the icons span over a long period of six centuries, the same stratification comprising gypsum ground layer, paint layers prepared by modified "egg tempera" techniques (proteinaceous materials mixed with oil and resins), and varnish layer is revealed in the investigated samples. Moreover, the presence of three layers of varnishes, one at the top and other two as intermediate layers, in the cross-section analysis of a sample from Virgin and Child provide evidence of later interventions.