Photo: Example of a historical sample, measuring system and output quantities from a 3D DIC measurement. The sample is subjected to humidity fluctuations which result in the formation of displacements and change of its shape.
Monitoring changes of Cultural Heritage objects
Cultural Heritage (CH) objects represent the history and identity inherited from our ancestors, and it is our responsibility to safeguard and protect them for future generations. One way of protecting them is to understand the changes they undergo over time and record them. But one might wonder, what do we mean by changes?
Changes might refer to different features such as: shape, deformation, damage or colour of an object and they are linked with the properties (for example chemical, structural, mechanical, optical etc.) of the material. When the recording of an object changes is distributed in time according to a certain protocol, we call it monitoring. The analysis of the collected information help us to track the response of the object caused by a variety of external factors including humidity, temperature, mechanical loading, exposure to air pollution and many others. The most practical way to collect this information is to apply vision based methods which can deliver data in the full field-of-view (FOV) and in contactless manner.
Therefore, Athanasia Papanikolaou, Early Stage Researcher (ESR) 15, is working on the design and building of a portable and low-cost device to record, monitor and measure changes that happen in CH objects over time. To achieve this, three different quantitative imaging techniques will be combined (namely Structured Light, 3D Digital Image Correlation and simplified Multispectral Imaging) into a single scanner that will be able to record the 3D shape, displacements/strains and spectral content of the studied objects in situ. Using this information, we can develop methodologies and protocols to determine safe storage or displaying conditions, conservation strategies or assess environmental changes, while at the same time we create a digital record of the object for future generations.
For this reason, Warsaw University of Technology has established a good collaboration with the Warsaw Academy of Fine Arts. There, we get the chance to work side by side with conservators and face open conservation challenges, combining the field of optical metrology and conservation. At first, we had jointly selected the groups of Cultural Heritage objects (painting, ceramics, parchment and marble), which require the full-field monitoring by means of all modalities. Next, she focused on the modifications and implementation of 3D Digital Image Correlation technique for monitoring and analysing displacements and strains in CH objects exposed to environmental changes. For example, you can find the recently published study (EI 2021 paper), which focuses on monitoring the response of a parchment to fluctuations of relative humidity using 3D Digital Image Correlation (3D DIC). In this work they positioned the 3D DIC system consisting of two cameras on a rigid bar within a humidity chamber in which they mimic part of the relative humidity fluctuations happening in storage rooms, without controlled environment, due to the change of the seasons. With their system they tracked the shape (h(x,y,z), in-plane displacements (u(x,y) and v(x,y)) and out-of-plane deformations (w(x,y)) that the parchment sample can undergo if appropriate fixation of a parchment is not used. An example of such a measurement can be found in Fig.1, where the sample, the system and representative results of shape and displacements are shown. The historical parchment sample was exposed to relative humidity difference equal to 20% resulting into the creation of displacement and change in its shape. In general the aim of this collaborative project is to create an affordable tool with significant potential in the hands of conservation scientists for the monitoring of cultural heritage objects as well as the development of protocols that will ensure their safety and digitization.