Abstract 3D laser and optical scanning techniques are widely employed in Cultural Heritage preservation for documenting pieces of different sizes and shapes. However, due to limitations of the methods available today, the results obtained vary according to different characteristics of the object under study. External surfaces showing very smooth features make the capturing process and the posterior processing a more elaborate task, requiring special attention and additional retouching to improve the final 3D model. Tombstones are a typical example of this type of objects, combining both flat external contours and refined outlines. In this work the procedure of creation of the digital model of the tombstone of the bishop Vasilije Petrović (Negosh) is described, a piece of art which combines both technical and historical importance. Post-processing steps required involved different software (Geomagic Design X, ZBrush, Adobe Photoshop) for surface correction and cleaning, details and photorealistic texture improvements and lost material restoration.

This paper is devoted to investigation of laser cleaning of paper with fat-containing contaminations. In recent years, laser technologies have been widely used in the preservation of Cultural Heritage (CH). One of the main fields of laser application in this area is the cleaning of CH objects from natural and anthropogenic contaminations. It is known that there exist two main approaches to the laser cleaning, e.g. dry cleaning and wet cleaning. We will present experimental results of wet laser cleaning with the Ytterbium fibre laser (wavelength of 1064 nm) of fat-containing contaminations from model samples and fragments of a real historical artefact such as XIXth century book.

The article presents experimental results related to the use of Raman and laser induced breakdown spectroscopy for chemical analysis, as well as to the study of the composition of historical inks Examples of qualitative spectral analysis of four types of model ink as well as the original ink of the manuscript “The Gospel According to Luke Explanatory” are presented. The given ink replicas created on the basis of an authentic recipe were applied to cotton pulp paper, which underwent artificial heat and moisture aging. The obtained spectra were recorded using a Raman Confocal microscope. The presented results of interpretation of the spectra show the possibility of qualitative analysis of model ink samples and original ink of the manuscript, their comparison and obtaining the expected similarity of compositions. The disadvantages of this method were identified as well, and it was proposed to compensate for them using laser induced breakdown spectroscopy.

3D printing techniques are widely used nowadays in different areas, thanks to its replication speed, good accuracy, good material reliability and low cost. Everyday these techniques are applied in new and diverse fields, employed for testing purposes, replication and reconstruction tasks and even to substitute complex and hard to replace mechanical parts. However, there are different methods available in the market with various reproduction accuracy degrees depending on multiple factors like physical properties of the used materials. To evaluate these issues, we used three popular 3D printing technologies (FDM, SLA and SLS) to reproduce geometrical primitives created in CAD software with the goal of evaluating how these different techniques represent important features of these particular figures like hard edges and plain surfaces.

Nowadays, in restoring and examining paintings, the search for effective analytical methods for studying paint pigments is very actual. The identification of poor pigments is important itself, but it is also important for the determination of pigments in paints with different binders. Many studies were done in this field by means of Raman and IR Fourier spectroscopy, X-ray fluorescence spectrometry and some others. However, all the mentioned methods require the use of complex and expensive equipment, sampling, and preparation of samples. For this reason, the search for new simple non-destructive, and inexpensive testing methods is still very actual. In this work for studying color characteristics of pigments, the spectrophotometry method was used. In the experiments, the color characteristics of model samples were studied. It was shown that the color characteristics of pigments and paints, including, for example, whitewash (lead, zinc, and titanium), have characteristic individual values of the color coordinates L*a*b* that may be used for their identification.

In this work, a painted gypsum bas-relief from the facades of the inner courtyard of the St. Petersburg Academy of Arts building was examined using UV and visible light photography and optical and electron scanning microscopy, which showed the heterogeneous layers of white painting on the surface of the bas-relief that covered the historical ones. These undesirable layers should be removed during the restoration work, but it was found that the traditional method of removing surface layers of painting with the help of chemical solvents and mechanical cleaning does not solve the problem to the full extent. A cross-section of all the painting layers was prepared to investigate the stratigraphy of the paint layers. These studies were conducted using optical and electron scanning microscopy in order to determine the structure of the paint layers more properly and study the chemical composition of every layer. After this study, a complex cleaning technique was developed. This technique combines chemical and laser cleaning, making it possible to effectively remove the upper dense layers of paint without damaging the historical paint layers.

Subject of study. This work was devoted to the removal of foxing spots from the pages of books and paper documents. Aim of study. The aim was to determine the output parameters of lasers that would allow the effective and safe removal of foxing. Method. Pulsed lasers were used in the experiments: a solid-state Nd:YAG laser with a wavelength of 0.53 mu m and an excimer ArF laser with a wavelength of 0.193 mu m. Main results. The highest foxing removal efficiency was achieved when the ArF laser was used for the treatment. The best results were achieved when using wet laser treatment in the case of paper containing wood pulp fibers and dry treatment for paper containing wood pulp. The optimal output characteristics of the ArF laser, which effectively removed foxing spots, included an energy density of 0.21-0.34 J/cm2, pulse repetition rate of 1-2 Hz, and pulse duration of 10 ns. A technique for quantifying the foxing removal effectiveness based on an analysis of digital optical images of the studied section of a book or document before and after laser treatment was proposed and experimentally verified. This technique is easy to use and does not require expensive analytical equipment. The research showed the high efficiency of foxing laser removal from the long-term perspective. Practical significance. The results obtained in this study showed the advantage of the laser treatment of books and paper documents with foxing spots compared with traditional restoration methods and recommend this technology for practical restoration work in libraries and archives. (c) 2024 Optica Publishing Group

This article is focused on the study of the possibility of the restoration of the lost decorative color appearance of iron-based metal artworks. An ytterbium fiber laser (1064 nm) was used to irradiate carbon steel surfaces. Laser-induced color oxide layers of blue, yellow, brown, and white colors were obtained on the surface of carbon steel by adjusting the main laser radiation parameters: power, repetition rate, beam scanning speed, and pulse duration. In experiments, we used mockups on the surface of which colored oxide layers had been obtained by means of laser treatment. Then we damaged the oxide layers, creating artificial corrosion, and reproduced the original color appearance by means of several stages of laser processing, including cleaning, polishing, and local heating of the mockups' surfaces. The conducted studies show that the application of lasers is a promising method for the reconstruction of the color appearance of iron-based cultural heritage objects.

The work examined a fragment of the 18th-century bas-relief (metope) from the courtyard facade of the St. Petersburg Academy of Arts building. As a result, a combined method was developed for cleaning a gypsum bas-relief from surface paint layers using a chemical solvent of dimethyl sulfoxide in combination with laser cleaning technology. Comparative analysis with the area cleaned by the traditional method showed that the area cleaned by the combined cleaning method had a more uniform color without visible surface damage.

At the moment 3D imaging is one of most powerful tools for documenting Cultural Heritage (CH) objects that makes possible their high-precision virtualization and representation. Nowadays this approach is frequently used in a routine base in many museums around the world. Meanwhile, a considerable number of CH objects found in underwater scenarios are documented and restored on site, following the newest trends in the CH preservation field. Our paper is devoted to 3D imaging of underwater CH. We will present overview of state-of art of underwater 3D scanning and photogrammetry. We analyzed features of underwater 3D imaging and mathematical algorithms which are most effective at creation of computing 3D models objects documenting in underwater environment. Preliminary experimental results of underwater 3D imaging also will be presented.

This paper is devoted to investigation of chemical and mechanical paper properties after laser cleaning. In recent years, laser technologies have been widely used in the preservation of Cultural Heritage (CH). One of the main fields of laser application in this area is the cleaning of surfaces of CH objects from natural and anthropogenic contaminations. However, cleaning of books and documents on paper basis requires intensive experimental studies. Comparison of paper properties before and after laser cleaning may prove the safety of laser cleaning. One of the most important parameters that characterize paper strength and durability are hydrogen ion concentration (pH) and absorptivity. We will present experimental results on pH value measurements of paper as well as results on paper absorptivity performed on model samples and real historical artefacts such as books and fragments of newspapers. The results of studies indicate on the neutralising effect of laser irradiation which can be used for the conservation of books and documents on paper base.

The purpose of this work is the study of laser cleaning of historical paper. The effect of laser exposure of the paper reflectance, fracture resistance and acidity was investigated. The paper surface roughness before and after laser treatment was analyzed by optical and scanning electron microscopy. It was shown that use of multi-pulse micromachining in combination with high-speed scanning of laser beams provides high safety for paper cleaning. The optimal parameters of laser radiation for effective and safe cleaning are a power density of about 2 × 105 W/cm2 at a wavelength of 1.06 μm, pulse repetition rate is 20 kHz; and a beam scanning speed of 200 mm/s–500 mm/s. The selective laser cleaning method for books and documents was proposed. Selective cleaning is achieved by means of high-precision control of the trajectory of movement of laser beams.

This article is devoted to the study of the possibility of the passivation of iron-based metallic materials. The experimental results obtained for the laser treatment of carbon steel model samples by the radiation of repetitively pulsed and continuous-wave 1.064 µm Nd:YAG lasers are described. It is shown that the laser treatment allows the formation of dense protection films, 62–77 microns thick, on the steel surface. The films enhance the anticorrosion properties of the metal. Exposure to laser radiation reduces the surface roughness (from Ra = 0.53 µm to Ra = 0.38 µm). Laser radiation power densities of 10.2 × 105 W/cm2 and 10.7 × 105 W/cm2 for these two laser generating modes, respectively, correspond to the optimum (in terms of the degree of corrosion resistance) modes of steel treatment. The conducted studies show that the application of Nd: YAG lasers is a promising method for the surface passivation of artworks created from steel and cast iron. One of the most promising applications of the proposed method for the anticorrosion protection of iron is the passivation of the surface of iron-based historical monuments.

3D laser and optical scanning are widely used in the engineering field to obtain digital representations of complex surfaces. Its high precision and harmless working principle make it an invaluable tool in Cultural Heritage Science. One recent application for 3D scanning is the monitoring of the conservation state of oil paintings. Two studies were carried out in 2014 and 2019 on an oil painting that is part of the collection of the Military-Historical Museum of Artillery, Engineer and Signal Corps (St. Petersburg, Russia) to evaluate its preservation progress over a period of time. In 2021 a new study was performed with a 3D structured light scanning device. The goal of this work is to show how 3D scanning can be used as a tool to continually evaluate the conservation status of this type of fine art and verify for signs of aging, comparing the obtained results in the different studies.

Single dielectric microspheres can manipulate light focusing and collection to enhance optical interaction with surfaces. To demonstrate this principle, we experimentally investigate the enhancement of the Raman signal collected by a single dielectric microsphere, with a radius much larger than the exciting laser spot size, residing on the sample surface. The absolute microsphere-assisted Raman signal from a single graphene layer measured in air is more than a factor of two higher than that obtained with a high numerical aperture objective. Results from Mie's theory are used to benchmark numerical simulations and an analytical model to describe the isolated microsphere focusing properties. The analytical model and the numerical simulations justify the Raman signal enhancement measured in the microsphere-assisted Raman spectroscopy experiments.

3D laser and optical scanning are advanced technologies that are widely used for creation of state-of-the-art, highly accurate documentation of physical objects being of particular importance in Cultural Heritage to preserve the most precise representation of a piece of art. However, the process of creation of a 3D model from data obtained on the process of 3D scanning is a complex procedure which implies the use of specific software tools to achieve good results. One of the phases is the alignment step (also called registration) which connects the data objects obtained after the scanning phase. This procedure might be done with the help of different software programs and algorithms, giving results that might differ. The goal of this work is to estimate the accuracy of creation of 3D models which can be created using different software tools that are usually employed for the alignment procedure.

3D laser and optical scanning technologies are invaluable tools in metrology applications, covering requirements of the most diverse fields of the scientific activity being Cultural Heritage Science (CH) one of them, where researchers and practitioners rapidly implemented their use allowing them to create highly accurate digital 3D models of real-life objects while preserving the objects condition thanks to their non-destructive working principle. Nonetheless, creation of 3D models starting from scanning procedures involves complex and time-demanding post-processing tasks that must be done by highly trained professionals who use different available tools to reach the final output and, as a consequence of this, the results might greatly differ in terms of reproduction accuracy, important requirement in CH field both in terms of measurement accuracy and observer’s perceived reproduction quality, depending on the application in which the resultant model will be used. Along this work, in which the scientific novelty resides in the study of the influence of the human factor over the accuracy of the creation of 3D models of objects of CH, we compare the results of three different post-processing procedures done by different operators with distinct experience in the area, we study the tools employed in each case, the main differences that feature the results and investigate how a common agreement is needed to try to reduce the gap between the finished models, in the search of reducing to a minimum the so-called human factor in creation of digital 3D objects for CH.

Three-dimensional laser scanning is a novel measurement technique that is frequently used for the documentation of cultural heritage (CH) objects. In the process of 3D scanning, one can obtain computing 3D models of artworks to be documented. It allows one to produce detailed digitized archives of important CH objects. Moreover, the use of 3D scanning enables the digital reconstruction of architectural fragments, sculptures, and other artworks. One more important application of this technique relates to the creation of molds and replicas for replacements of outdoor CH objects in case their preservation requirements do not allow them to remain in their original place due to the influence of environmental factors. One of the most effective ways of creating replicas is the use of laser additive technologies. Therefore, the combination of 3D scanning and additive technologies is a very promising way of preservation of CH. This paper describes several case studies concerned with the combined usage of 3D laser scanning and additive technologies for digital reconstruction and replication and of outdoor sculptures in St. Petersburg city. One of them is the reconstruction of the zinc sculpture “Eva at the fountain” (XIX century, England), which was destroyed during WWII. Its replica was created by means of laser stereolithography. Eventually, one more project is related to the reconstruction of the fragment of the sufficiently damaged cast-iron XIX century monument. This object was reconstructed using two laser technologies: direct metal laser sintering (DMLS), and laser cladding (LC).

The article describes laser cleaning of paper. In recent years, laser technologies were increasingly used for the preservation of the Cultural Heritage. One of the main fields of laser application in this area is the cleaning of CH objects from natural contaminations and anthropogenic pollutions. Compared with mechanical and chemical cleaning methods traditionally used in the restoration, laser cleaning technology has a number of important advantages, such as high efficiency and "delicacy" for the removal of contaminants. The paper presents experimental results on laser cleaning of paper including model samples and real artifacts (fragments of old newspapers).

Optical characteristics of minium pigment layers were studied using the time-resolved THz spectroscopy method. The special software were created for fast automation of data processing. The results can be used for pre-restoration diagnostics of easel paintings. In addition, they provide prerequisites for creating the technique of colorful thin-film coatings thickness controlling.