Catálogo de publicaciones - libros

The laser cleaning of painted artefacts relies on the synergy of thermal, photochemical and photomechanical effects, which are involved in laser ablation. A crucial issue, however, for a successful cleaning intervention is the spatial confinement and control of these effects for safeguarding the original surface from potential damage. Extensive studies have shown that in many cases there is an optimum interplay of laser and material parameters, which resulted in successful laser cleaning applications. The laser pulse duration is an important parameter in this context.

A powerful sensor system providing both high-resolution textures and highly accurate 3D geometry information is created by combining near-range photogrammetry and terrestrial laser scanning. As both sensors are integrated closely into a single system, the textures can be applied to the 3D data automatically and with high precision. These sensors have proven as extremely valuable tools in applications of cultural heritage, architecture, and archaeology. We demonstrate the capabilities of the RIEGL LMS-Z420i system with an integrated high-resolution camera by presenting the work flow of data acquisition and postprocessing performed for modeling St. Stephen’s Cathedral in Vienna, Austria, with an emphasis on the construction of CAD models.

This study deals with the analysis and characterisation of historic patinas on Spanish buildings from the sixteenth and seventeenth century by means of laser induced breakdown spectroscopy (LIBS). Indicative results from the analysis of these samples are shown. LIBS can be proven as an appropriate technique to characterise patinas and assist in a rapid and facile classification. The prospect of developing portable LIBS equipment makes the technique attractive for carrying out analyses on site.

The fluorescence spectra of historical and model paper samples, previously irradiated with the laser beam at wavelengths of 1,064, 532, 355, and 266 nm, are recorded under excitation at 266 nm, and the nonirradiated samples are used for reference. The spectral profiles obtained for the laser-treated model papers made of cotton and/or linen only reveal differences compared to the reference ones. After irradiation at 532 and 1,064 nm, a decrease of the band intensities of the entire spectral profile is observed. In contrary, the UV irradiation at 355nm of the same samples results in the increase of bands centered at 341 and 370nm compared to the visible region only. Prolonged treatment at 266nm results in the marked increase of band intensities in the visible region and corresponds to the independently observed yellowing.

Before starting the cleaning program of the peristyle of Diocletian Palace in Split, a series of tests have been performed on it. First of all, the state of conservation of columns and capitals has been assessed applying non-destructive techniques such as thermography, magnetoscopy and superficial ultrasonic tests. All the areas with black crusts, exfoliation and stone cracks have been determined. In this stage, parameters such as water absorption and colour have been estimated in order to compare them with those measured after the cleaning operation. Then, more than 3-month period of tests have been performed to set up all the parameters concerning the application of the laser cleaning techniques. In this chapter, the results of these preliminary investigations are presented.

Raman spectroscopy, being a laser spectroscopic method, is gaining increasingly more interest for applications in the field of art and archaeology. The technique is especially appreciated for its non-destructive character, the speed of analysis and the ability to obtain molecular information on a whole range of materials, organic as well as inorganic. Although the Raman effect was observed for the first time in 1928, it was not until the end of the 1980s before instrumental improvements enabled the analysis of micro-samples, and thus allowing the application of this method in archaeometry.

In this study, tests were undertaken to ascertain whether the laser could achieve a better level of cleaning on polyurethane foam than vacuum cleaning. Optimum laser parameters were found using statistics on data from color measurements. The laser proved to be very effective regarding the removal of dust, but also caused damage on some PU-variants. The laser cleaning has been carried out at National Workshops for Arts and Crafts, Copenhagen, Denmark.

Laser metrology provides techniques that have been successfully applied in industrial structural diagnostic fields but have not yet been refined and optimised for the special investigative requirements found in cultural heritage applications. A major impediment is the partial applicability of various optical coherent techniques, each one narrowing its use down to a specific application. This characteristic is not well suited for a field that encounters a great variety of diagnostic problems ranging from movable, multiple-composition museum objects, to immovable multi-layered wall paintings, statues and wood carvings, to monumental constructions and outdoor cultural heritage sites. Various diagnostic techniques have been suggested and are uniquely suited for each of the mentioned problems but it is this fragmented suitability that obstructs the technology transfer. Since optical coherent techniques for metrology are based on fundamental principles and take advantage of similar procedures for generation of informative signals for data collection, then the imposed limits elevate our aim to identify complementary capabilities to accomplish the needed functionality.

The Lyre of Ur was one of two bull’s-headed harp instruments that British archaeologist Sir Leonard Woolley recovered from a mass grave during his highly publicised excavations of Ur’s Royal Cemetery in the 1920s and 1930s in Iraq. Recreated unplayable models of the Lyre are held in Pennsylvania, London and, until recently before it was vandalised, the Baghdad Museum. It is believed that the original Lyre is approximately 4,750 years old. An attempt to recreate an authentic playable version is being spearheaded by Mr. A. Lowings of Stamford. The instrument is to be ornamented by a golden-sheeted bull’s head and geometrically inlaid lapis lazuli as well as engraved gulf pearl shell plaques depicting Sumerian images, which are to be placed on the front of the lyre. Authentic cedar wood from Baghdad was used to create the main framework of the lyre. Due to the intricate designs required for the shell plaques, an investigation to laser engrave them was undertaken.

Laser divestment entered the field of art conservation through a nonlinear sequence of positive accidental events (serendipity) that involved the cinema industry, the invention of spread-spectrum and frequency-hopping communications, nuclear space propulsion, and oceanography. The unlikely chain of events began with the invention of a secure military communications system by a Viennese motion picture actress (1942). A first evaluation of the novel communications concept took place during a high-altitude nuclear test (TEAK) over the Pacific Ocean in 1958. The secure radio link proved to be a failure; however, analyses of the backscattered electromagnetic radiation contributed to the realization that nuclear-explosion plasmas need not be spherically symmetrical. Nobel Laureate Freeman Dyson exploited this nuclear option to guide in the design and prototype development of the ORION spaceship that was to rendezvous with the planet Saturn in 1970.