La Coupole: a revolution in the conservation of heritage objects

The conservation of heritage objects is a complex and multi-dimensional issue that aims to preserve cultural artefacts for future generations. Works of art, ancient clothing, historic monuments and archaeological objects make up our cultural heritage. However, they are often exposed to a variety of deteriorating factors, including environmental conditions and wear and tear over time. Their preservation is therefore essential to maintain historical and cultural continuity.

Beyond mere physical preservation, the conservation of works of art and heritage objects raises important ethical issues: each intervention on an object must respect its historical and artistic integrity. This is why restorers have to make delicate decisions about the restoration of works, which must firstly maintain their original state, while secondly defining the interest of maintaining their accessibility to the general public and under what conditions. This tension between conservation and restoration is at the heart of current debates in the field of cultural heritage. 

"Many works of art are not exhibited in museums, not because there is not enough room for them, but because they have to be conserved under specific conditions of temperature, light, etc." explains Romain Pacanowski, a researcher in the Manao project team behind the La Coupole project. With this in mind, digitisation and the creation of digital copies of works of art offer new opportunities for conservation and accessibility, making it possible to protect the originals while at the same time making cultural heritage accessible to a global audience and to professionals (scientists in the human and social sciences, restorers, etc.).

La Coupole represents a significant advance in the digitisation and conservation of heritage objects. This innovative system combines several cutting-edge technologies to create highly detailed digital replicas of the appearance of rare and ancient objects.

The project was born just over 10 years ago in collaboration with the Musée d'Ethnographie at the University of Bordeaux. "Our aim was to be able to digitise heritage objects, in this case 19th century clothing from one of the Trocadéro Museum's national collections, with the same quality on screen as the human eye can see in real life," continues Romain Pacanowski. "To be able to do this, we had to take into account a number of constraints imposed by the museum's curators: not taking the collections out of the building, not touching them, always measuring the exposure time, and not using ultra-violet light so as not to damage the objects...".

Created by the Manao project team to meet these objectives and constraints, La Coupole is a hybrid system that acquires both the geometry and reflectance of the object under study. "Reflectance is a physical quantity that describes how a material will reflect light," explains Romain Pacanowski. "It's a very important parameter to master when you want to create ultra-realistic computer-generated images. In 3D, we observe materials at different points, so we need to be able to describe at every point how the material will react to light".

To acquire the reflectance of objects, a high-performance optical system combining cameras and LEDs is integrated into La Coupole, recording colorimetric information and ensuring that the digital replicas faithfully reflect the original colours of the works. To complement this, high-resolution 3D scanners capture the exact geometry of the objects, producing digital models that faithfully reproduce every detail, from the smallest relief to the texture of the surface. 

© Arthur Pequin

In addition to the scientific and technological challenges that the Manao project-team is meeting with La Coupole, the latter also poses a number of important challenges for the conservation and promotion of cultural heritage. Firstly, "it facilitates the study and transmission of these heritage objects, documenting the materials used and the manufacturing, assembly and decoration techniques", explains Romain Pacanowski, for scientific, restoration and educational purposes.

Another major challenge is to reduce the risks associated with handling and exhibiting heritage objects. With La Coupole, museums and institutions can create digital copies for virtual exhibitions, minimising the need to handle the originals. What's more, these replicas can be shared with a global audience, increasing the accessibility of works of art without the risks associated with transport and prolonged exposure.

The Coupole can also play a crucial role in art history and conservation research. The data collected by the device enables ethnologists to study artistic techniques, the materials used and the processes by which works of art deteriorate with unprecedented precision. This could lead to new discoveries and more effective conservation techniques.

The future outlook for La Coupole is vast and promising, particularly through its involvement in ambitious new projects such as the VESPAA project, which involves the high-fidelity rendering of African objects held in various museums (Musée d'ethnographie de Bordeaux, Musée d'Aquitaine, Muséum de La Rochelle and Musée d'Angoulême) in the Nouvelle-Aquitaine region. "The main objectives of this project are to improve the quality of the measurement data acquired in order to represent complex materials (gilding, pearling, patina and varnish) and to develop multi-resolution representations to visualise the digitised objects in real time and with a high degree of fidelity under dynamic lighting conditions and viewing directions," points out Romain Pacanowski.

In addition to the VESPAA project, the Manao project team is also involved in the European Automata project. A new post-doctoral student will soon be joining the team to work on a prototype in Italy that will include a conveyor belt similar to those used in airports and an optical dome inspired by La Coupole to digitise heritage objects. The project also aims to integrate robots using innovative concepts to enhance digitisation methods.

Ultimately, La Coupole aims to develop a metrological approach to the digitisation of heritage, with the European xDDiff project: "The aim is to establish with precision the uncertainties involved in measuring the reflectance of digitised objects, going beyond the simple production of aesthetic images," adds Romain Pacanowski. This approach will guarantee the reliability of measurements and digital representations of objects, consolidating La Coupole as a key tool in the metrology of appearance. By establishing precise standards, this project promises to transform the digitisation of heritage into an exact science, benefiting partner museums and the conservation of cultural heritage.

Digital technology to the rescue of works of art - Science En Questions (video in French), L'Esprit sorcier, 06/14/2024.