e. prior to the occurrence of phenomena related to irreversible damage) is critical for technology innovation in preventive conservation.In this paper, fundamental research on direct measurements of dimensional responses of model samples which follow induced humidity fluctuations is presented. Measurements can be used to determine dimensional changes on a micro-scale using non contact laser instrumentation based on Optical Holographic interferometry principles and results suggest that these measurements can further the understanding of mechanisms of damage and deterioration. The perceptible changes that eventually occur, and the material responses that vary, can be studied in order to distinguish between phenomena which result from natural ageing from those related to or aggravated by climate-induced deformation.

Ideally, Optical Holographic interferometry can be used to inform risk assessment of individual objects, to predict specific future deterioration, and for the establishment of realistic environmental values based on concrete data for museum galleries.In this work, Optical Holographic interferometry Non Destructive Testing (HINDT) methods are proposed for revealing small material displacements in the range of few to some tens of micrometers and for identifying hidden flaws or heterogeneities in dimensional response as well as damage or the onset of plastic deformation (or fatigue) [26-29].

The technique is completely non-invasive, nondestructive and fully non-contact, allowing the examination and assessment of any object regardless of size or fragility; therefore, the methods can routinely be used to analyse art works and sensitive historic artifacts for incipient faults, the onset of deterioration, or the assessment of long-term damage. Hence HINDT allows the adoption of corrective measures at an early stage, or can inform treatment of damaged objects [30-37]. This method represents an alternative and significant improvement to the use of other displacement Drug_discovery sensors which require contact and the fixing of a sensor to the surface of a work of art [38, 39].Moreover the direct non contact recording of deformation or displacement following small variations in the environment on works of art represents a promising field of sensor research and development of relevant instrumentations and methodologies [40-42]. In this work, the dimensional changes due to natural or imposed environmental fluctuations is exploited and used as a dimensional sensor to indicate damage levels and calibrate baseline values for structural stability under specific loads [29].