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LACONA is the most renowned international conference in the field of lasers application to conservation. The conference gathers together every two years researchers and conservator-scientists to share their latest projects and experiences. For those involved in this area of our profession, the conference is an up-to-date record of experience, achievements and recently proposed solutions for laser technology applied to conservation of works of art.
The use of lasers in conservation is not new; it dates back to 1972 when John Asmus first applied laser cleaning to marble sculptures. Since then, laser technology has opened new doors of knowledge in conservation, not only in laser cleaning but also in the analytical field. Over the last three decades, much research has been done and technology has developed considerably. From 1995, when LACONA first took place, up to the latest edition - LACONA VII held in Madrid in 17-21 September 2007 - the conference seems to bring together more participants and more diverse, advanced contributions. This time the book of proceedings was published in August 2008 by CRC Press in a carefully bounded, full colour hardcover edition. As expected, the volume brings to light recent studies and developments, for both the already established laser systems applications and the newly explored, innovative approaches used to address usual and less usual conservation problems. The book gathers 77 contributions organised in 10 sections according to their thematic: Innovative Approaches in Laser Cleaning and Analysis; Analytical Techniques; Portable Laser Systems for Remote and On-Site Applications; Laser Cleaning of Monuments and Sculptures; Laser Cleaning of Paintings and Polychromes; Laser Cleaning of Metal Objects; Laser Cleaning of Documents and Textiles; Structural Diagnosis and Monitoring; Imaging and Documentation; and Miscellaneous. It has become a tradition that the very first article of the proceedings is authored by John Asmus, who is considered to be the grandfather of laser art conservation. Encouraged by his early discovery of laser cleaning in Venice (Italy) in the 70’s, John Asmus continued testing and applying laser to clean several materials. The paper now presented, “Photonic restoration of marine artefacts and vessels of New Spain”, documents his extended experience with laser cleaning in Ballas Point, San Diego Bay (USA). Among other uses, the author describes laser cleaning tests of several archaeological artefacts such as fossils, coins and wood, and diverse equipment including that used for underwater laser cleaning. The opening section of the book is “Innovative approaches in the laser cleaning and analysis”. It counts 8 articles that summarise the latest technologic advances in the field. In laser cleaning, the growing use of femtosecond lasers should be noticed, which offers shorter pulse duration minimizing potential damage to the surface, and may be used for the chemical reconversion of pigments. Nowadays most analytical techniques are based on laser technology, which is closely connected to any industry that we can think of. Its application to art conservation is of high importance and our understanding of art and art materials wouldn’t have been so advanced without it. The section dedicated to analytical techniques is the largest of the book, containing 13 papers. The diversity of techniques, their applications and further case studies makes impossible their reference in this review. However it is worthwhile reading and I have found especially interesting the article concerning the thermal decomposition of basic lead(II) carbonate by San Andrés et al. This single paper explains in detail the thermal decomposition process that involves historical lead-based pigments, in particular the production of litharge, massicot and lead white. The paper is an important addition to the current research on laser induced degradation of pigments, a possible side effect of laser cleaning. In case of immovable cultural heritage, portability of laser systems is a major concern because the most likely scenario is that the monument requires on-site treatment. In fact, only a limited number of objects may be transported to the laboratory or workshop and therefore the development of portable laser systems for laser cleaning and analysis is a priority. In particular, the section dedicated to portability of lasers systems comprises research made with different types of lidar based systems. Lidar stands for Light Detection and Ranging and it is a remote sensing system used to collect topographic data. One of the most known but also intricate and demanding laser applications is cleaning. There are four sections fully dedicated to laser cleaning of several materials, namely stone-based materials (monuments and sculptures), painted surfaces (paintings and polychromes), and metals and organic materials such as paper documents and textiles. The section dedicated to the laser cleaning of monuments and sculptures is surprisingly short containing only 5 papers. I say surprisingly because this section is the only one specific to the cleaning of stone-based materials which has been the main cleaning application for considerable years. In particular, the section contains case studies of architectural decorations and a study of granite stone. Again to my surprise, there is only a single case study of sculpture cleaning, that of ivory statues cleaning with Nd:YAG laser. The largest section is the one dedicated to paintings and polychromes, a remarkably growing field of research. In fact, a safe interaction of paintings and laser radiation is one of the most difficult processes to achieve due to the high sensitivity of the paint layer. Safety procedures dictate that the removal of varnish - the most often use of laser cleaning of paintings followed by removal of dirt deposits – should be only partial in order to avoid discolouration. The papers of this section present the actual state of the art in this domain. All the papers describe actual case studies of paintings with several laser types, namely Nd:YAg, KrF and Er:YAg. Among these, Er:YAG laser attracts more attention because of the limited research of its applications. One of the characteristic properties of this laser is that by working at 2.94 µm it requires the presence of –OH groups either at the surface or within the material composition. I would like to refer here to two papers in particular. The first is “Laser cleaning of stucco’s fragments from an early middle age bas-relief” where Sansonetti et al. applied mostly laser cleaning with a Nd:YAG system but also compared the results obtained with that system with an Er:YAG laser. The Nd:YAG laser was found more suitable for that type of support because it allowed to conserve the patina while the Er:YAG produced a “whitish surface”. Furthermore, Camaiti et al. studied “the interaction of laser radiation at 2.94 µm with azurite and malachite pigments”. It was found that wetting agents were required in order to avoid pigment discolouration and that tenorite is an alteration product of both pigments. I welcome these researches but the fact that so far the effect of this wavelength has not been completely understood in many materials makes me wonder if the commercial Er:YAG systems are being well used. The last section is dedicated to imaging and documentation. A high-profile paper presents the case study of the Mona Lisa: “Ultra high-resolution 3D laser colour imaging of paintings: the Mona Lisa by Leonardo da Vinci” by Blais et al. I have already come across some news about this project on the internet but this is the first detailed paper I found about it. The project describes the 3D scanning process that a team from the National Research Council of Canada (NRC) made of the Mona Lisa painting. The scanning of both the painting and the reverse side was made with the support of a custom built 3D scanner with a depth resolution of 10 µm. The importance of the painting obviously attracts public attention but the most important fact, in my opinion, is that the development of the technique and the type of information that painting researchers have now access to have a huge potential. Last but not least, a paper that is also of high interest for painting conservators is “Multi IR Reflectography” by Fontana et al. The authors developed a high resolution reflectography scanner that works in the 800-2300 nm spectral range. The scanner recollects the image from 14 spectral bands which offer high quality information from the inner layers of the paintings. This is way further than what common reflectography equipments have ever achieved and I wish conservators will have access to such equipment in a near future. A book of proceedings is not always an easy read due to its diversity of areas and applications. However, conservators and other professionals most interested in new technologies and their applications to art conservation will most definitively appreciate the reading. Rui Bordalo is a paintings conservator with a strong interest in technology development for conservation, particularly in the application of lasers to the cleaning of paintings, subject on which he focused his PhD research.
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