On development of portable digital holographic speckle pattern interferometry system for remote‐access monitoring and documentation in art conservation

Abstract

AbstractArtworks are delicate objects representative of the most high values of human kind that require constant control over the situation they are in and effective actions to preserve them and deliver them safely to next generations. As such, the non‐destructive or minimally destructive nature of operator–artwork interactions has been considered as essential in this field. The complete diagnosis of the status of the art object signifying a full knowledge of invisible defects and their morphology allows its timely and correct maintenance and ensures its durability. It is herein presented the basic technical information on the development of a portable system termed Digital Holographic Speckle Pattern Interferometry (DHSPI) for the structural diagnosis of works of art. DHSPI has been tested on a variety of conservation problems over the years. It is a completely portable and fully PC driven automated system for the detection and non‐destructive diagnosis of the structural alterations of an artwork, whether they are defects lying on the subsurface or between the layers below it, the fringe number information allows the depth estimation and the complete documentation. The system exploits the benefits of a highly coherent laser beam as essential presupposition for remote on‐field access—that is the main emphasis given here—to immovable/movable art objects. It takes advantage of a CCD camera as photosensitive medium to record the interference of the retro reflected object laser beam from the object under consideration with a twin reference laser beam. The device allows micro projections of the defects on the surface of the object to be detected with a resolution that corresponds to half the wavelength of the laser beam. Local disparities, in relation to the total response of the object, are directly correlated to the detected microdisplacement of object surface as structural defects. Special tailor‐made software allows full control of the system, processing of the data, and extraction of anomalies. Direct visual qualitative observation of the displacement processes is followed as captured in the monitor. A second custom‐made software—not presented in detail here—enables further processing of the results to improve their imaging, quantification, and dimensioning. The final result is a quantitative map of alterations, the coordinates, and the classification of their risks which can be also extracted if further information is necessary. The qualitative or quantitative documentation map can be used as a guide to the conservator for maintenance and restoration work. Further on, the system also allows observation of the object's response to climate changes in order to predict the formation of alterations or the evolution of existing ones providing the only known direct tool for scheduling preservation strategies.