The potential of portable TV holography for examining frescoes in situ

The authors describe the application of TV holography, also known as electronic speckle pattern interferometry (ESPI), to the examination of wall paintings. The equipment uses fibre-optic illumination and a solid-state camera connected to a computer. Images made after the wall painting has been warmed slightly with an infrared lamp are compared with reference images; differences in the speckle pattern can be used to identify cracks and subsurface detachments. The system is robust and portable, allowing it to be used for the in situ investigation of wall paintings, including those exposed externally. It can also be used to monitor the condition of the work of art over time and to evaluate the success of any treatment.