Micro-Multiband Imaging (µMBI) in the Technical Study and Condition Assessment of Paintings: An Insight into Its Potential and Limitations

Multiband imaging (MBI) is a non-invasive, portable digital technique that has become increasingly widespread in the technical study and condition assessment of paintings, owing to its affordability and ease of use. This paper presents an experimental study aimed at optimising MBI at the microscopic scale—referred to as micro-multiband imaging (µMBI)—with the particular aim of expanding its diagnostic capabilities. A range of µMBI techniques was used on custom-made mock-ups made up of pigments selected for their spectral responses, and representative of traditional artistic materials. The techniques used included microphotography of polarised and unpolarised visible light (µVIS), raking light microphotography (µRL), transmitted light microphotography (µTL), ultraviolet-induced visible luminescence microphotography (µUVL), near-infrared microphotography (µIR), near-infrared micro-trans-irradiation (µIRT), and near-infrared false-colour microphotography (µIRFC). The results obtained through µMBI were compared with those from standard MBI methods, allowing for a critical discussion of the strengths and limitations of this emerging approach. Results evidence that µMBI provides high-resolution, spatially specific insights into materials and painting techniques, offering a more detailed understanding at the microscale of how a painting was executed. It also enables the assessment of deterioration processes (e.g., cracking, delamination, and metal soap formation), contributing to a deeper comprehension of the origin and progression of failure phenomena and supporting the development of more informed, preventive conservation strategies.