The potential of OCT for assessing laser assisted removal of deposits from ceramic tiles

Abstract

Optical Coherence Tomography (OCT), the technique of non-invasive imaging of transparent and semi-transparent sub-surface layers was employed to monitor the state of glazes of historic tiles before and after laser ablation trials. The laser used was Nd:YAG Thunder Art system from LightForArt (El. En. S.p.A.). In this paper, OCT cross-sectional images of both fragments and preserved historic tiles before, during and after laser ablation are shown to examine the process of the removal of surface deposits as well as mid-twentieth century conservation coatings. In case of some of the ceramic fragments (donated to science) the destruction of the glaze layer after a few steps of laser cleaning was induced intentionally and then visualized with OCT. The experiments performed confirmed that OCT is a potential diagnostic tool for the assessment and monitoring of laser removal of deposits from semi-transparent glazes on historic tiles, as well as enabled to define and identify specific risk factors for these objects, such as pre-existing cracks or delaminations within the glaze layer.

Advanced procedures in Raman forensic, natural, and cultural heritage studies: Mobile set‐up, optics, and data treatment—State of the art and perspectives

“…Thus, it is required that the operator knows or can make hypotheses about the material structure and stratigraphy. Appropriate techniques such as Optical Coherence Tomography (OCT) 57,58 could F I G U R E 1 On-site Raman analysis: top, HE532 Horiba Jobin Yvon coupled with 532 nm Ventus laser and SuperHead ® equipped with a ULWD 200X Mitutoyo microscope objective (bottom, zoom) provide this information but are rarely used, the common approach being to presume that the characteristics of the objects are comparable to those of similar ones (incomplete, broken, and revealing their stratigraphy). Suitable optics and a good knowledge of the volume of material generating the Raman signal are also necessary.…”

OCT for Examination of Cultural Heritage Objects

“…The use of lasers for ablation of unwanted layers (such as varnishes or mineral deposits) from paintings and other objects is a particularly delicate operation which needs precise control. Feasibility studies presented at LACONA (Lasers in the Conservation of Artworks) conferences in 2007, 2013, and 2015 [36][37][38] proved that it is possible to efficiently monitor such a process in real time. A specific case of removal of unwanted layers from the substrates of mural paintings was addressed by Striova et al firstly in the case of removal of shellac varnish [39] and then of calcium oxalate layers [40], in both cases by means of laser and chemical treatment.…”

Complementary use of Optical Coherence Tomography (OCT) and Reflection FTIR spectroscopy for in-situ non-invasive monitoring of varnish removal from easel paintings

“…Scale bars in all the tomograms shown in the figures are equivalent to 100 μm (in varnish of n R = 1.5) in both directions. In this contribution, OCT data are presented not only in the form of cross-sectional images (tomograms), but also as en-face images (differential maps) [23] of examination areas, which enable assessing the bulk of material removed in every step. In order to generate such maps, from 3D OCT data cube collected after every cleaning step and composed of 150 B-scans, a surface profile was extracted.…”