Bogumiła J. Rouba

The Application of Optical Coherence Tomography to Non-Destructive Examination of Museum Objects

Abstract The application of Fourier domain optical coherence tomography (FDOCT), a new implementation of incoherent light interferometry, to the examination of museum objects is described. The technique has been applied to the examination of porcelain and faience ceramics, and to the investigation of paintings. Time-resolved optical coherence tomography was used to study the surface profile of a painting during changes in the environment surrounding the object. The method provides precise section and surface profiles with micrometer resolution, and is complementary to other optical methods.

Optical Coherence Tomography for Tracking Canvas Deformation

Preliminary results of the application of optical coherence tomography (OCT), in particular in its spectral mode (SOCT), to tracking of deformations in paintings on canvas caused by periodical humidity changes are presented. The setup is able to monitor the position of a chosen point at the surface of a painting with micrometre precision, simultaneously in three dimensions, every 100 seconds. This allows recording of deformations associated with crack formation. For the particular painting model examined, it was shown that the surface moves in-plane towards the corner, and bulges outwards (Z-direction) in response to a rise in humidity. Subsequent to the first humidification/drying cycle, translation in the Z-direction is decreased, whilst in-plane translations increase somewhat. It was also shown that the response of the painting on canvas begins immediately on changing the relative humidity in the surroundings.

Application of digital image correlation (DIC) for tracking deformations of paintings on canvas

A non-invasive and non-contact optical method for tracking overall and local deformations of canvas painting is presented. The technique was tested on a model painting on canvas with inhomogeneities introduced by infilling gaps, mending tears, and applying patches on the reverse of the canvas. The deformation of the sample was induced by changes of relative humidity. The feasibility of 3D Digital Image Correlation technique for evaluation of conservation methods is discussed.

Application of 3D digital image correlation to track displacements and strains of canvas paintings exposed to relative humidity changes.

This paper introduces a methodology for tracking displacements in canvas paintings exposed to relative humidity changes. Displacements are measured by means of the 3D digital image correlation method that is followed by a postprocessing of displacement data, which allows the separation of local displacements from global displacement maps. The applicability of this methodology is tested on measurements of a model painting on canvas with introduced defects causing local inhomogeneity. The method allows the evaluation of conservation methods used for repairing canvas supports.

Optical Coherence Tomography for non-destructive investigations of structure of easel paintings

In this contribution the application of Optical Coherence Tomography (OCT) for non-invasive structural imaging of easel paintings will be presented. Since the technique permits imaging semi-transparent layers accessible for infrared light, the varnish and glaze layers are usually under investigation. The major emphasis will be laid on application of OCT to resolving specific conservation problems, arising during the restoration process. The examples of imaging multilayer varnishes and subsequent alterations will be given and the application of these images for authentication of inscriptions will be discussed. Since the thickness of imaged layers may be directly measured with OCT in completely non-destructive, quick and convenient way as many times as necessary, the application of the technique to generation of varnish thickness maps will be presented.