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.
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