Abstract:In this paper we demonstrate that optical coherence tomography (OCT) is a powerful tool for the non-destructive investigation of transparent coatings on metal substrates. We show that OCT provides additional information which the common practice electrical impedance spectroscopy (EIS) cannot supply. First, coating layer thicknesses were measured and compared with reference measurements using a magnetic inductive (MI) measurement technique. After this validation of the OCT measurements, a customized sectioned sample was created to test the possibility to measure coating thicknesses with underlying corrosion, which cannot be analyzed accurately by MI or EIS measurements. Finally, we demonstrate the benefit of OCT on a standard sample. The OCT measurements provide the correct coating layer thickness with high lateral resolution and even enable metal and corrosion layers to be distinguished from each other.
Identifying the most vulnerable plastics and monitoring their deterioration is one of the main problems within heritage collections with historical synthetic polymers. Gathering and interpreting data about material and degradation phenomena in a collection reveals its conservation needs. A systematic survey of the collection can help towards this purpose. Surveys aiming at inspecting and documenting damages rely on several tools in order to fulfill their purpose. Firstly, objective descriptions of the damages that may appear, and secondly, the means of acquiring and interpreting material information. To address these needs, this article presents (a) a visual damage catalogue of degradation phenomena in plastic and rubber materials, and (b) the implementation of Fourier-transform infrared spectroscopy (FTIR) and pyrolysis–gas chromatography–mass spectrometry (py-GCMS) for the identification of analytically challenging rubber materials and of blooming phenomena. The damage catalogue is based solely on visual and olfactory signs, so that the assessment is independent of possible causes of damages and underlying processes, with the purpose of allowing objectivity to prime over interpretation. The limitations of the use of FTIR in the identification of heavily compounded rubbers in museum surveys is highlighted, and examples are presented. The use of py-GCMS on these cases conveniently allowed the identification of the constituting monomers of several rubber materials where FTIR could not provide a univocal classification of the material present. The study of several cases of blooming allowed the identification of diverse compositions and origins, showing that the description of a degradation phenomenon is only the first step towards its understanding. Unveiling the nature of a particular case of blooming is particularly critical when conservation treatments, such as the removal of a (potentially protecting) layer, are planned. For this purpose, attenuated total reflection-FTIR (ATR-FTIR) as a surface technique was particularly useful.
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