Non-invasive quantitative characterization of varnish thickness on gilt leather by line-field confocal optical coherence tomography

Line-field confocal optical coherence tomography (LC-OCT) is an alternative to conventional OCT that combines OCT and confocal microscopy. This technique gives access to three-dimensional (3D) images with a micrometer resolution in the three spatial directions and enhances signal from the deepest layers within the material. After an experimental determination of the device characteristics, the technique is used for the investigation of16th to 18th century fragments of gilt leathers wall-hangings. In these objects, the various layers within the varnish can be identified and the effect of a restoration treatment can be observed to validate the varnish removal process.