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Comparison of optical methods for characterization of glass mosaic weathering
Kocour, Vladimír ; Petráňová, Veronika ; Valach, Jaroslav
The work presented in this paper is a part of research project supported by Ministry of Culture and devoted to conservation of precious mosaic of 'Last Judgement' on St. Vitus Cathedral in Prague. The aim of the project is to enhance external protective polymeric coating on glass tesserae of mosaic and also to develop optical method for assessment of coating’s surface conditions. The paper concentrates on comparison of various methods for surface evaluation assesses their advantages and disadvantages and also discusses their suitability for long term monitoring of coating state, namely reflectometry, scanning probe microscopy, nanoindentation, white-light interferometry, and scanning electron microscopy. It is found that white-light interferometry and reflectometry methods are the most suitable ones for monitoring purposes.
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Assessment of vibrations in museum's environment
Valach, Jaroslav ; Wolf, Benjamin ; Paulová, E. ; Urushadze, Shota
This paper deals with measurement of mechanical vibrations and accelerations threatening objects in museum collections. Two case studies are presented. The first case analyses situation in museum exhibitions strongly influenced by street traffic in its close proximity. It compares results obtained by sensitive professional measurement system to the custom-built user device for acceleration recording. The second case analyzes object’s accelerations during transport based on measurement by the custom-built device.
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Semiautomatic Surface Reflectance Measurement for Monitoring of Material Weathering
Kocour, Vladimír ; Valach, Jaroslav
We present a device for measurement of surface reflectance in dependence on incidence angle and reflectance angle. This measurement enables us to quantitatively determine how much the surface is glossy or matt. The device is programmable, which enables us to choose non-equidistant steps of angles, and study special situations more in detail. It can be used for monitoring of material weathering or other types of degradation as weathering usually causes that the surface becomes more matt.
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Determination of drift distortion in SEM micrographs acquired at different magnifications and acquisition times
Petráňová, Veronika ; Koudelka_ml., Petr ; Valach, Jaroslav
In the experimental mechanics wide variety of optical methods including measurement of deformation at reduced length scales using combination of computer vision and scanning electron microscopy (SEM) have been recently applied. One of suitable methods for in-plane measurement of displacements and deformations in the micrographs obtained by SEM is the 2D digital image correlation. In contrast to images obtained in visible spectrum by classical optical devices temporally-varying distortions known as drift distortion are present in the SEM micrographs. These distortions are caused by positional errors of electron beam during scanning process. Magnitude of this effect decreases with higher conductivity of the sample and is also influenced by magnification and scanning time. For this purpose measurement of distortion was performed on a series of micrographs of conductive samples acquired at different magnifications and acquisition times. Surface of each sample was covered with liquid silver to ensure adequate contrast pattern necessary for determination of distortion’s magnitude and distortion magnitudes were assessed.
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Investigation of Optical Properties of Protective Layer for Glass Medieval Mosaic of Last Judgement from St. Vitus Cathedral in Prague
Valach, Jaroslav ; Kocour, Vladimír ; Černý, Miloš
The Mosaic of Last Judgement from St. Vitus Cathedral in Prague is a medieval masterpiece created in late 14th century by Venetian craftsmen. If very dramatic history and various problems encountered are taken into consideration, the current state of preservation is acceptable, perhaps mainly due to systematic effort to protect the valuable item of cultural heritage. The research project, part of which is presented here, also aims on developing effective means for preservation of the precious object. It concentrates on finding formula for creation of protective layer that eliminates influence of chemicals present in air and in water, while being stable itself. The main goal of the investigation is to help in finding the best formula for protective layer that is most stable itself, i.e. which does not represent a future obstacle in viewing the mosaic, e.g. because of losing its transparency.
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