KEYWORDS: Ultraviolet radiation, Luminescence, 3D modeling, Cultural heritage, Diagnostics, 3D image processing, 3D applications, Projection systems, Light emitting diodes, 3D image restoration
This contribution presents some examples of the application of ultraviolet fluorescence (UVF) photography and photogrammetry on cultural heritage objects and paintings. The used approach is based on low-cost systems sustainable in terms of costs for restorers and conservators, but, at the same time, able to supply valid and relevant information for a better knowledge of the preservation state, of previous restoration interventions and of possible superimposed materials. This knowledge is fundamental for planning and addressing the restoration activities, such as cleaning and consolidation, in the most appropriate way as possible. Specific cases studies will be reported concerning large paintings and 3D objects. In the first case, it has been necessary to acquire several images by dividing the surface into various parts, as function of the dimensions of the investigated area, and then by using photogrammetric tools to recompose the images into a single one (orthophotomosaic of the painting). In the second case, the UVF images are acquired all around the 3D objects and then processed in order to obtain a photorealistic model under ultraviolet fluorescence. The image acquisitions were obtained by using a digital camera equipped with different lens and filters. Lighting of the surfaces was obtained by UV projectors. The acquired images have been then processed through photogrammetric tools in order to obtain the final 2D and 3D ultraviolet fluorescence outputs of the investigated artworks that can be explored and profitably used for gathering metrically precise information and material response to UV radiation.
The main purpose of this contribution is to report some first preliminary analyses of a new and never investigated decorative technique named Tattoo Wall, especially the possible changes due to ageing artificially induced by extreme humidity conditions in view of a possible application in crypts, churches or outside wall paintings. This innovative decorating technique involves transferring digital images on wall surfaces through a transfer paper with solvent-based ink and fixative. For the experimental tests, we chose to work on a color scale as wide as possible, to test each single color, and on different materials. The printed colors were applied on hydraulic mortar, containing marble powder combined with Ledan C30, particularly suitable for restoration in environments with high relative humidity (RH%). Moisture ageing was obtained by placing the sample in a box with RH% fixed to 92% thanks to the presence of salts (sodium sulphate deca-hydrated) for compressively two years (96 weeks). Reflectance spectrophotometry for color measurements and hyperspectral imaging (HSI) were used to assess the effect of high relative humidity exposure. The experimental data were statistically treated in order to evaluate their significance. Testing enabled us to verify the stability and durability of Tattoo Wall® under high relative humidity, with little chromatic alterations. Testing could and should be conducted also on different surfaces and materials (paintings on canvas and wood, oil on wall, etc.) to make it as complete as possible and guarantee the use of Tattoo Wall® in most cases of pictorial reintegration, reducing the risk of human error.
The focus of this study was to investigate the potential of hyperspectral imaging (HSI) in the monitoring of commercial consolidant products applied on wood samples. Poplar (Populus spp.) and walnut (Juglans Regia L.) were chosen for the consolidant application. Both traditional and innovative products were selected, based on acrylic, epoxy, and aliphatic compounds. Wood samples were stressed by freeze/thaw cycles in order to cause material degradation without the loss of wood components. Then the consolidant was applied under vacuum. The samples were finally artificially aged for 168 h in a solar box chamber. The samples were acquired in the short wave infrared (1000 to 2500 nm) range by SISUChema XL™ device (Specim, Finland) after 168 h of irradiation. As comparison, color measurement was also used as an economic, simple, and noninvasive technique to evaluate the deterioration and consolidation effects on wood. All data were then processed adopting a chemometric approach finalized to define correlation models, HSI based, between consolidating materials, wood species, and short-time aging effects.
The focus of this study was addressed to investigate the potentiality of HyperSpectralImaging (HSI) in the monitoring of commercial consolidant products applied on wood samples. Poplar (Populus Sp.) and walnut (Juglans Regia L.) were chosen for the consolidant application. Both traditional and innovative products were selected, based on acrylic, epoxy and aliphatic compounds. Wood samples were stresses by freeze/thaw cycles in order to cause material degradation. Then the consolidants were applied under vacuum. The samples were finally artificially aged for 168 hours in a solar box chamber. The samples were acquired in the SWIR (1000-2500 nm) range by SISUChema XL™ device (Specim, Finland) after 168 hours of irradiation. As comparison, color measurement was also used as economic, simple and noninvasive technique to evaluate the deterioration and consolidation effects on wood. All data were then processed adopting a chemometric approach finalized to define correlation models, HSI based, between consolidating materials, wood species and short time ageing effects.
The focus of this paper is to show the work experiences with laser cleaning on sculptures made of terracotta, plaster,
wood and wax. These materials exhibit peculiar features that often prevent the use of traditional cleaning procedures to
remove the surface dirt, soot or carbonaceous deposits and other materials coming from environment or ancient
conservative interventions.
To overcome the difficulties in the cleaning of the above mentioned materials, laser technology was tested. The laser
irradiation and cleaning tests were carried out with a Q-switched Nd:YAG system under the following conditions:
wavelength 1064 nm and 532 nm; energy 4-28 mJ; pulse duration 10 ns; spot diameter 2-8 mm; frequency 5 Hz. The
irradiated surfaces were analyzed before and after the laser tests, with the aid of a video microscope and a reflectance
spectrophotometer, in order to evaluate the morphology and colour changes of the surfaces.
Before starting with the cleaning intervention, some diagnostic analysis was performed on the sculptures in order to
obtain the identification of the original materials and of the surface deposits. Concerning this, Fourier Transform Infrared
spectroscopy, X-ray fluorescence spectroscopy, and internal micro stratigraphic analysis were performed.
This research demonstrated that the laser cleaning is an effective method to remove the surface deposits preserving the
original patina of the sculptures and the opacity of the wax.
The results gathered in this work encourage to continue the research in order to better understand the interactions
between the laser beam and the surfaces and to find the most appropriate laser conditions to clean the sculptures.
The aim of this work is to study the surface modifications of poplar (Populus spp.) wood by reflectance spectrophotometry and Fourier Transform Infrared (FT-IR) spectroscopy in order to understand the mechanisms that cause the changes and to suggest possible solutions to avoid the degradation phenomena. Since colour changes on wood surfaces are due to photo degradation of its chemical constituents, the study of the relationship between CIELAB colour changes and changes in chemical composition due to irradiation is of practical importance both in cultural heritage and in contemporary artefacts and objects.
Concerning the surface protection of wood, starting from the results obtained by testing different commercial products, the attention has been focused on Linfoil®, a novel organic preservative/consolidant product that seems to attract a great interest in the field of conservation of wooden artefacts. Linfoil® was chosen and analysed in order to understand its composition and its time stability using reflectance spectrophotometry, FT-IR spectroscopy and analytical pyrolysis coupled to a gas chromatographic-mass spectrometric system.
Colour monitoring allowed to find that wood surface colour undergoes an important variation due to photo-irradiation, occurring within the first 24 hours and mainly due to L* decrease and b* increase. Though Linfoil® treatment modifies wood colour, nevertheless it seems to protect wood surface by reducing the yellowish. FT-IR spectroscopy allowed to investigate the rate of photo-degradation of wood surface due to lignin oxidation. The most important result is that a correlation of the colour changes may be derived with the photo-degradation of lignin obtained by FT-IR analysis.
In this paper two case studies on the application of colour measurements for the evaluation of some
restoration materials are discussed. The materials related to the research are: watercolours employed
in restoration of wall paintings and preservative/consolidants for wood artifacts.
Commercial watercolours, supplied by Maimeri, Windsor&Newton and Talens factories have been
tested. Colour measurements have been performed by means of a reflectance spectrophotometer
(RS) before and after accelerated ageing of watercolours at 92% relative humidity (RH) and in a
Solar Box chamber. The experimental results show that watercolours based on natural earths and
artificial ultramarine undergo the main colour changes, expressed as L*, a* and b* variations and
total colour difference (▵E*). In the other cases colour differences depend on both watercolour
typology and suppliers.
The other example concerns the evaluation of colour change due to surface treatment of Poplar
(Populus sp.) and chestnut (Castanea sativa L.) wood samples. The wooden samples have been
treated with a novel organic preservative/consolidant product that has been tested also in a real case
as comparison. The treated samples have been artificially aged in Solar Box chamber equipped with
a 280 nm UV filter. Colour has been measured before and after the artificial ageing by means of a
RS. Colour changes have been determined also for the main door of an historical mansion in
Viterbo, made of chestnut wood, and exposed outdoors.
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