Catálogo de publicaciones - libros

The applicability of spectral optical coherence tomography (SOCT) for noninvasive and noncontact assessment of varnish layer thickness and structure on easel paintings is discussed. The SOCT tomograms of such objects are presented.

The present work focuses on the main phenomenological features of stone cleaning by lasers. They are the removal rate, degree of cleaning, and chromatic appearance of the treated surface associated with different conservation problems and laser parameters. A set of three different outdoor stone conservation problems were investigated here. The measurement of the ablation rates were carried out on encrusted stone artefacts and two sets of prepared samples in order to derive general behaviour through repeatable measurements. The analysis of the irradiation tests provided a quantification of the different efficiencies, degree of cleaning, and chromatic appearances associated with the fundamental harmonic of Q-switching, long Q-switching, and short free running Nd:YAG lasers (1,064 nm), as well as with the second harmonic of Q-switching sources (532 nm).

Results of laser cleaning experiments on different gilding types like leaf gilding and fire gilding are presented in this contribution by means of three tested art objects. The reflectivity of gold is advantageously high for the typical laser cleaning wavelength of 1,064 nm. Additionally, to avoid damage like gold loss, the transfer of the absorbed laser pulse energy into the art object by thermal conduction is considered. Fire gilded surfaces are most easily cleaned because of the good heat transfer conditions which imply a high threshold intensity with respect to damage. This is different for leaf gilded surfaces but suitable laser cleaning parameters have also been found for this case. The results of laser cleaning experiments are presented by photography, microscopy, SEM and EDX analysis.

The use of laser cleaning within the conservation field in the United Kingdom has tended to be restricted to indoor work within the studios of a small number of national museums and private conservation companies. This paper describes one of the first large-scale projects to be carried out on a public building in the United Kingdom.

In this work a series of egg tempera paint and varnish systems have been prepared, artificially aged and irradiated with KrF excimer laser at a wavelength of 248 nm. The samples were prepared with pure pigments and selected mixtures. It was found that, for some pigments, the colour changed upon laser irradiation even at low energy densities, below the ablation threshold while for other inorganic pigmented egg temperas the degree of discoloration is very small at moderate fluence of ∼ 0.30 J cm ? 2. The varnish systems did not present signs of discoloration. The thickness, superficial roughness and magnitude of the colour changes of the samples were measured. X-ray diffraction, Raman spectroscopy and UV/visible spectroscopy were used in order to investigate the changes induced by the KrF excimer laser radiation.

The most widely known application of holographic and speckle interferometry (termed HINDT, ESPI, or DSHI) is in the sensing of invisible structural flaws, which are represented visually as discontinuous interference patterns. This property raised laser metrology techniques as the candidates best suited for nondestructive detection of subsurface defects in qualitative assessment of artworks [1–6].

A fluorescence lidar measurement has been performed on the castle Övedskloster in Sweden. A mobile system from the Lund University was placed at ∼ 40m distance from the sandstone façade. The lidar system, which uses a frequency tripled Nd:YAG laser with a 355-nm pulsed beam, induces fluorescence in each target point. Areas were studied by using whisk-broom scans. The possibility of detecting biodeteriogens on the surface and characterization of materials was confirmed. The method can be a tool for conservation planning and status control of the architectural heritage where fluorescence light can point out features that are not normally visible under natural illumination.

This work, aimed at quantifying the morphological variations induced by laser cleaning on stone materials, represents a very first attempt for a new quantitative means to reveal changes in stone surfaces. It is a three-dimensional survey carried out by means of laser micro-profilometry and completed by statistical data processing. The acquisition and successive computation is performed on small selected areas both before and after the cleaning process.

The Abergavenny Hoard is a recently discovered collection of late Saxon and Norman silver coins, the details of which were badly obscured by corrosion products and iron concretions. A Q-switched Nd:YAG laser, using near infrared radiation at 1,064 nm, was employed to clean the hoard. Detail retained on the surface of the coins after laser cleaning included “rough-out” marks and polishing marks from the original die, as well as the legend. From this evidence surface damage appears to have been minimal, and the treatment very successful.

A large-scale survey ( ∼ 700m2) of frescoes and wall paintings was undertaken in the US Capitol Building in Washington, DC to identify regions that may need structural repair due to detachment, delamination, or other defects. A common approach for post-processing time series called Proper Orthogonal Decomposition, or POD, was adapted to frequency-domain data in order to extract the essential features of the structure. We present a POD analysis for one of these panels, pinpointing regions that have experienced severe substructural degradation.