Surface layers analysis of bronze artifacts by means of laser spectroscopy techniques

Abstract

Abstract-Advantages of the complementary use of spectroscopic techniques are exemplified by the analysis of a historical bronze mortar from XV c. performed as part of the running collection conservation project by the National Museum in Gdansk. The bulk material and surface layers are analyzed by means of the XRF and µ-Raman techniques. Quasi-nondestructive LIP (Laser Induced Plasma) spectroscopy delivers additional data on the elemental composition and is applied also for stratigraphic sampling across the surface layers.A detailed understanding of the environmental impact on historical metal artefacts is of considerable importance for their preservation. In most cases, the poor state of historical metal objects and collections being a significant part of our cultural heritage results from prolonged exposure to adverse environmental conditions This paper presents the results of analysis of the material and patina of the historic bronze mortar (Fig. 1) by means ofRecently, systematic research on historic collections and case studies show that the combination of spectroscopic and optical techniques for elemental, compositional, and structural analysis enhance greatly the reliability of results [2][3]. Moreover, non-destructively operating instruments allow us to keep the impact on valuable and precious objects extremely low.complementary spectroscopic methods, which ensure reliable characterization of the object. The bronze mortar (XV c.) produced by casting has a bell shape and a rectangular handle * E-mail: izmuda@imp.gda.pl -see Fig. 1.Typically, the gothic mortars were decorated with reliefs based on architectural motives. The object under investigation originates most probably from Gdańsk and represents a modest version of the dish characterized by a smooth, not ornamented coat. Dishes of this type were popular in Northern Europe in the fifteenth century. The mantle just above the foot is slightly bellied with a little horizontal crack visible on the surface. The entire surface is covered with a homogeneous layer of brown patina with the exception of the foot edge. The light reflection on the surface may originate from the protection layer applied during previous conservation. Small t An elemental analysis of the object was carried out races of a greenish-coloured patina are present on the foot reverse and the handle, too.non-invasively by means of an X-ray fluorescence spectrometer (XRF) completed at IF-FM PASci. The spectrometer X-ray tube IS601.5 (Italstructures) used for excitation has produced an excitation beam collimated to a spot of 4 mm in diameter. The tube was operated at 50kV and 1mA, and ensured detection of elements in the range from K (19) to U (92). During measurements an accumulation time of 120s for recording of each spectrum was applied.The XRF results were supplemented by the LIBS data in order to increase the level of confidence of the detected elements. The LIB spectra were recorded under pulsed excitation with an Nd: YAG laser (Quantel) operated at 1064nm and energy density of 2J/cm -2 ...