LIBS ANALYSIS AND LASER CLEANING OF METAL OBJECTS RESCUED FROM THE CORVETTE H.M.S. SWIFT

G. M. BILMES; F. C. ALVIRA; N. PEREZ ZOLOZA; A. A. ORSETTI

Laser in the Conservation of Artworks IX

Archetype Publications

Lugar: Londres; Año: 2012; p. 179 - 181

On March 13, 1770 as a consequence of a storm the war corvette H.M.S. SWIFT stranded and sank at the Patagonian coast in the Deseado Ria, Santa Cruz, Argentina, at 50 meters from the coast. It came from a military base located in Puerto Egmont, in Malvinas islands. Its mission was the exploration of the Patagonian coast. The corvette had been built by the British army in 1762 and it was a small and light ship of 27. 94 meters long, with 26 canons. It was prepared to transport a crew of 125 men, but at the moment of  sinking it had only 91, and three of them died during the storm. On February 4, 1982 a group of enthusiastic students created a commission for the search and rescue of the Swift objects. Since then, more than 500 objects have been  rescued by the Instituto Nacional de Antropología de la Argentina and now belong to the Museo Municipal Mario Brozoski located in the city of Puerto Deseado,  Santa Cruz Province, Argentina. Most of the objects have concretions and different degree of corrosion. Before restoration and conservation in many cases it must be necessary to identify the main composition of the substrate, to decide the appropriate treatment that requires each object. This is the case of many metal pieces for which the high degree of marine corrosion makes impossible, by simple inspection, to determine the main composition of the piece. Chemical and structural analysis of archaeological objects provides also important information about the techniques and procedures used for the manufacture of the objects. For this purpose several analytical techniques can be used. Among them, Laser –induced Breakdown spectroscopy (LIBS) has significant advantages over conventional, analytical techniques for applications to unique pieces of heritage value.1-3 LIBS is based on the spectroscopic analysis of the light emitted by the plasma generated by ablation of the sample with a laser pulse. When qualitative composition of an object is required LIBS has its optimal performance. Since samples do not require prior preparation (analysis can be performed directly on an object of any shape and dimension), measurements are fast and easy to perform. LIBS has also the possibility of deep profiling characterization.4 This work is part of an ongoing project that applied the LIBS technique for identifying the elemental composition of objects belonging to the war corvette HMS SWIFT in order to implement the appropriate conservation treatment. Previous results showed the feasibility and advantages of LIBS for this purpose.5 Here, LIBS was applied to the characterization of 23 metal objects. They are a collection of spoons, buckles, coins, buttons, bullets, and other metallic pieces . Laser cleaning of some of these objects was also performed. We discuss the advantages of LIBS for characterization of the composition of underwater objects previous to restoration.